Index Librorum Prohibitorum

Index Librorum Prohibitorum (禁書目録 (インデックス) ) is the eponymous character of Toaru Majutsu no Index. Commonly known as Index, she is the main female character of the Magic Side; in Toaru Majutsu no Index series. She is a member of Necessarius and has a. She holds within herself 103,000 magical texts known as grimoires.

Etymology
Her name is based on the book with the same name, or "Index Librorum Prohibitorum" (禁書目録) in Japanese. It is a list of publications prohibited by the Roman Catholic Church.

The avowed aim of the list was to protect the faith and morals of the faithful by preventing the reading of immoral books or works containing theological errors, although it also contained scientific works by leading astronomers, such as Johannes Kepler. The various editions also contained the rules of the Church relating to the reading, selling and censorship of books. It was abolished on 14 June 1966 by Pope Paul VI.

Appearance
Index is small in stature, has a petite build, and, much to her chagrin, a flat chest. She has thigh-length, silvery-white hair, and large green eyes. She is also often seen wearing her Walking Church, a white, and modified nun's habit with gold highlights. It is an accurate replica of the Holy Shroud of Turin and offered Index ultimate protection from most attacks, however, it was destroyed by Touma's right hand. She still wears it, though safety pins are now needed to hold it together.

Personality
Due to being raised in a church and having no memories of her life up until a year before she met Touma, Index is quite innocent and naive, often being elated by things that an adult or even people her age would find mundane. She is slightly ignorant and curious of modern technology, not knowing what a touchscreen was or how it worked until Hyouka Kazakiri showed her.

She is very gentle and polite with people and has a kind nature, as shown when she picked up a stray kitten and took it home, although Touma initially refused. She also, like Touma, has the trait of sacrificing herself for others sake which is why several people befriended her in the past who still keep caring for her despite her memory loss each year. Despite her naivety, Index is extremely intelligent, as a result of having the knowledge of 103,000 grimoires stored inside her. Due to her photographic memory, Index is able to remember everything in the books and often gives Touma information when needed.

She can be easily irritated especially when it comes to Touma, who usually ends up angering her in some way as a consequence of his own bad luck. He is often bitten by Index as punishment. It is a recurring gag for Index to bite Touma whenever he has inadvertently annoyed or irritated her in some way (much like Misaka Mikoto's habit of trying to electrocute him whenever she is annoyed at him), occurring even in serious situations or in front of important persons. She has even bitten him out of anger for trivial things that he has not even done. At one point, Touma even compares her to a mosquito. However, in Toaru Majutsu no Index no Subete, it is noted that it is a sign of affection towards him, as Touma is the only person whom she bites. Index can also be rather bratty at times, often getting annoyed when Touma doesn't spend enough time with her.

She also has an extreme appetite as shown when she met Accelerator and made him to spend all of his money treating her to food. In fact, the very first thing she said to Touma was that she was hungry. Index has taken a liking to the anime Magical Powered Super Android Girl Kanamin and once cosplayed as her. She has strong feelings towards Touma and even confessed her love after knowing Touma lost his memories because of her, however he avoided answering by changing the subject of the talk since he has no idea about what kind of feelings he used to have with Index.

Background
Much of Index's background is currently unknown because of the periodic memory loss that was brought upon her. Although, Index states that she was born and raised in St. George's Cathedral, there is not enough evidence to corroborate this, as Index as well is unsure of it.

It is not known if 'Index' is her true name or if it is a name given to her because she holds within her the 103,000 grimoires. It is confirmed that Index was specifically chosen as the vessel for the 103,000 grimoires because she has the ability to perfectly memorize things and also because she is unaffected by the books' debilitating effects. She possesses no mana and therefore cannot use the grimoires. She is accompanied by Stiyl around the world in order to memorize grimoires, from the Pataliputra ruins to the Vatican Library.

Later, after becoming the vessel of the grimoires, she was given partners as a means of protection. Three years prior to the start of the series, she was the partner of Aureolus Izzard, then a year later, Stiyl Magnus. Index's relationship with her partners is unknown because of her periodic memory loss, but it is implied that both Aureolus and Stiyl cared for her deeply. In Aureolus' case, he was Index's teacher during his time with her. It is confirmed that Kanzaki Kaori were best friends with Index before Index's memory was erased.

The church told lies to Kaori and Stiyl regarding the true nature of Index's memory being erased, as they planned to make the grimoires harder to access as well as because of their fear of Index betraying them or her apparently becoming a Majin. The church implanted a Collar and a multi-layered program that would disable her from using the magic of grimoires, as such she cannot access her mana, and therefore use magic, normally. To complete this defense, the Collar made Index extremely ill, and required an annual erasure of her memories.

Laura Stuart was the one that came up with this plan, as the alternative was to cut off all of Index's limbs and lock her inside the Tower of London to ensure absolute safety of Index Librorum Prohibitorum's knowledge from magicians that would misuse it, and to prevent her escape.

Index came to Japan a year before the start of the series, although she had already lost her memories prior to arrival, and has somehow awoken in a back-alley with at least basic knowledge regarding her position in the magic side. This was done as part of Stiyl and Kaori's plan to keep Index away from magicians that would misuse her knowledge, as Japan was seen to be a place with little history of magic according to them. Both Stiyl and Kaori believed it was for the best if Index spent the year running away from magicians as opposed to living through a year full of happiness, as then it wouldn't be as painful (for both themselves and Index) when her memory had to be erased. Index eventually ended up in Academy City as she was being chased by Stiyl and Kaori, because it was once again time to erase her memories. Moving from rooftop-to-rooftop during Academy City's unforeseen power outage, she slips and falls, landing onto the apartment balcony of the ever-unfortunate Kamijou Touma.

Toaru Majutsu no Index
Being the main heroine of Toaru Majutsu no Index, Index has a large role in the events of the story, alongside Touma.

Index Arc
Index first meets Touma while hanging over his apartment balcony. She remarks about how she is very hungry and would be extremely grateful if he could give her some food. Index introduces herself as a nun of Necessarius and reveals that she is being pursued by magicians, who are after the grimoires that she has. At first, Touma is skeptical of the existence of magic, but is quickly convinced of it as he is able to destroy Index's "Walking Church" using his right hand. After a lengthy discussion, Index decides to leave Touma's house, as she doesn't want him to have to get involved, Touma goes to stop her and Index asks if he would be willing to "follow her into the depths of hell". Touma hesitates at this question and Index smiles to herself before walking out, forgetting her headdress while leaving. Because of this she later has to return to Touma's apartment to retrieve it, but is attacked by Kanzaki Kaori, who seriously injures her, albeit unintentionally.

Touma returns home in the evening to find Index covered in blood and unconscious outside his front door, he is then confronted by Stiyl Magnus and a battle ensues. During this battle against Stiyl, Index falls under John's Pen Mode. She aids Touma by telling him that Stiyl has placed runes all over the building to aid him. Touma quickly deduces a counter-measure and Stiyl is defeated. After Stiyl's defeat, Touma takes Index to Tsukuyomi Komoe's house, as she is not an esper and is therefore capable of performing the ritual to heal Index. Index, still under John's Pen Mode, finishes the healing ritual with Komoe by summoning a replica of an angel, while chanting. Afterwards, she falls unconscious.

When Touma later returns, Index tells him of the existence of the Church of Necessary Evil, also known as Necessarius. Later, she and Touma go to a bath together where she reveals that she has lost all of her memories from the previous year. For one reason or another she assumes that Touma is angry about this and runs away. Sometime afterwards she discovers that Touma has been beaten to unconsciousness (by Kanzaki Kaori) and that he has been asleep since. Stiyl and Kaori come to the apartment for her, but Index believes that they are after Touma, and she tries to defend him, only for them to leave without trouble, however, they give Touma a time limit, after which they say they will return.

While Index is resting, Touma discovers the hidden mark within her that could destroy her if her memories aren't periodically erased. Touma touches the seal with his right hand and causes John's Pen Mode to activate. Index then attacks Touma, as well as Kaori and Stiyl, who have made good on their promise and returned. Kaori and Stiyl discover that they've been tricked by their church into believing that they needed to erase her memories. With the help of Kaori and Stiyl, Touma is able to defeat John's pen (and in the process, destroys Tree Diagram accidentally) but at the cost of Touma losing his memories.

The next day, Index visits Touma in the hospital, where the 'frog-faced doctor' tells her that his memories have been completely erased. Even so, Index pleads with Touma to remember her in a heart-felt speech, asking him to recall the things that had happened between them recently and even telling him that she loves him. However Touma surprises her by stating that his memories were not really destroyed and that his right hand has fixed the problem. Index becomes upset at him for joking about such things and bites him, leaving shortly afterwards. However, it is revealed that Touma lied about his memories because he couldn't bear to see Index cry.

Deep Blood Arc
Index and Touma go to a restaurant with Tsuchimikado Motaharu and Aogami Pierce where they meet Himegami Aisa. Index argues with Aisa after the latter claims that she is a magician, however, their argument is cut short when Aisa's teachers come to pick her up. When walking home with Touma, she discovers an abandoned kitten and decides to take care of it, much to Touma's disapproval. The cat runs off and she tries to give chase. Suddenly, she notices someone applying a magic spell and decides to investigate, leaving Touma alone. When she returns to Touma's apartment, she is carrying the kitten with her and has decided to name it Sphynx. Touma disapproves at first, but eventually relents and allows Index to keep Sphynx, much to her delight.

After Touma again leaves, Index eats the pudding in Touma's refrigerator, when Touma calls her he scolds her for it but suddenly disregards it. Later when Index is taking a bath she remarks on how Touma became distracted about something when discussing the pudding and decides to go find him. Index later arrives at the Misawa Cram School where she meets Aureolus Izzard, and although he is familiar with her, she has no idea who he is as her memories of him were erased. Index is later struck unconscious and sleeps through the whole battle between Aureolus (who is planning to turn her into a Vampire) and Touma, somehow dreaming blissfully of Touma and complaining to him of her hunger.

Index, along with Aisa and Sphynx, later visits Touma in the hospital. She tells him that the church is going to take care of Aisa from now on. She proceeds to eat the apples that Stiyl gave to Touma before Sphynx wreaks havoc in Touma's hospital room.

Sisters Arc
Index and Aisa try to find ways to get rid of the fleas that are infesting Sphynx until Touma comes home along with Misaka 10032, much to the jealousy of Aisa and Index. Misaka 10032 helps get rid of the fleas on Sphynx using her electrical abilities and proceeds to lecture Touma on how he should disinfect the room against more fleas before leaving. Later on, Index and Aisa decide to go to Komoe's house for food, seeing as Touma has yet to return home. During their time there, Index helps herself to food as Komoe explains to both of them how esper abilities work using Personal Reality. Komoe uses a chocolate ball inside of a box to demonstrate this to Index, who is frustrated at not being able to figure out what the box holds.

In the anime adaptation, they later go to a public bath, drink milk and enjoy massage chairs. Komoe continues to explain to Index and Aisa about esper abilities and the strange occurrence of Level 0's in the city. She also inadvertently reveals that many "naughty" things happened with Touma in the past while blushing heavily, which irritates Index and Aisa.

After Touma's battle with Accelerator, Index once again visits him in his hospital room. She gets upset and bites him for trying to go it alone and not asking her for help. This is followed up with a loving hug, and Index tells him how she worries about him and that the next time he fights, he should come to her first. Index asks him what he fought for this time, and Touma says that he fought for himself.

Angel Fall Arc
At Komoe's insistence, Touma and Index go to the beach for a vacation to lay-low until the heat on them from the "higher-ups" dies down. Index shows off her new swimsuit to Touma and gives him a jellyfish to the face, confusing it for a hat. Index later becomes disappointed when she discovers that the arrival of Touma's parents has been delayed, but Touma calms her down.

When everyone's physical appearances are switched due to Angel Fall, Index switches appearances with Aogami Pierce, much to Touma's horror. For the most part of the arc, Index gets abused by Touma for looking like Aogami Pierce and coming on to him. When they return to normal, Index derides Touma for her abuse at his hands and punishes him as-per-usual by biting him.

Fake Date
While Touma is on his fake date with Mikoto, unbeknownst to Index, she is watching an anime called "Magical Powered Kanamin" intensively until Touma calls her, asking her if she is alright and informing her that a magician is in the city. She aids Touma by telling him the nature of the weapon the magician is using. Touma is cut-off from her before she can berate him again.

Last Order
Accelerator passes by Touma's dorm building while Index and Touma are arguing during the early hours of the morning. He blocks the sound out with his vector manipulating powers.

Yamisaka Ouma
Index and Touma go to a diner. Touma is working on his homework, and Index lectures him on it. She reveals that what he is studying is a veiled occult book and one of the 103,000 grimoires contained within her, before being attacked by Yamisaka Ouma. Despite Touma's efforts, she is kidnapped by Ouma.

During her captivity, it is revealed that Ouma is trying to pull a book from her that will cure any sort of ailment which he needs because of a woman he had fallen in love with. Index pleads with him to stop as the spell would be harmful to Ouma himself, all the while Touma hears the events unfolding using the cellphone he gave to Index.

Touma arrives just in time and stops the ceremony before any further damage could be done to Ouma. He proposes to remove the curse of the woman Ouma fell in love with using his right hand.

Kazakiri Hyouka Arc
Index follows Touma to school because she is worried that she will not get any lunch due to the refrigerator being empty and Touma not being back until the evening. She successfully finds Touma's classroom but is then swiftly told by Komoe to go home. Index meets a mysterious person named Kazakiri Hyouka, who helps her to use a vending machine. They become fast friends and Hyouka helps Index fit in by giving her a school gym uniform to wear. Their fun is cut short when Touma accidentally walks in on them getting changed. He is once again bitten. Index introduces Touma to Hyouka and tells him that they are friends, she also warns Hyouka of Touma's tendency to attract women before they are interrupted by Komoe. Hyouka then suddenly disappears. Index is later seen depressed because she believes that Touma is angry with her and that he hates her. Hyouka, however, consoles her and tells Index that Touma is angry because he cares about her and because Index is his friend. Touma finishes his classes and keeps his promise to go somewhere with Index, he also invites Hyouka to come along.

Index is very enthusiastic when they visit the underground mall. The three of them eat and also play games, and once again, Touma accidentally sees the girls changing their clothes, which Index promptly punishes him for. Their fun is put to an end when they are forced to evacuate due to a disturbance in the underground. They learn that it is the work a magician. Touma decides to protect everyone with his right hand, but Index is against this, believing it is her job to go against magicians. When they hear footsteps approaching, Index and Touma trip over each other. Index then meets Misaka Mikoto for the first time but due to both girls’ affections for Touma they do not get along very well. Both girls demand answers from Touma on what his exact relationship is with the other. Touma asks Kuroko about the situation and learns that there is a terrorist in the underground mall and that, as a member of Judgment and being a teleporter, it is her duty to evacuate civilians. Touma asks Kuroko a favor- to teleport Index and Hyouka away but Index disagrees because it would mean Mikoto being left alone with Touma. Touma then asks Kuroko to teleport Hyouka and Mikoto but Mikoto then disagrees since that would mean Index would be left alone with Touma. Because of this, Kuroko is prompted to teleport both Index and Mikoto away.

Later, outside, Mikoto and Index complain about the hot weather. There, Mikoto asks Index why she is wearing a habit in such heat and then asks why her garment is secured with safety-pins, to which Index replies that she doesn't want to remember how it got ruined. Suddenly, Sphynx runs away and prompts Index to give chase, leaving Mikoto behind. However, Index comes face-to-face with the golem of Sherry Cromwell, whose target is now Index. Even though Index cannot perform magic, she is successful in holding back the golem by intercepting the commands given by Sherry to the golem using the safety pins from her clothing. However, the golem begins to act on its own and begins moving automatically, making Index's situation grim as she can no longer disrupt the golem's movements. Index is saved by Hyouka who reveals to Index that she is not really a human and states that "only monsters should fight other monsters". However, even with Hyouka's vast amount of power she is unable to hold-off the golem, and the two girls are eventually saved by Touma who finally destroys it for good.

Index later confronts Hyouka about her not being human and hugs her, confirming to Hyouka on Touma's statements that she is still human regardless of what she believes herself to be. After a talk about the untrue nature of Touma's powers, both she and Hyouka conclude that Touma's power can't be classified as magic or esper. Index then says her farewells to Hyouka as she returns to the Imaginary Number Sector. She tells Index that she will always be at her side, even if Index can't see her and promises to meet Index again one day before fading away.

Orsola Aquinas Rescue Arc
At the begin she is talking with Tsuchimikado Maika, showing her dissatisfaction that without Touma on home the thing gets boring and asks Maika why she isn't at her school, then thinks if she becomes a maid she can go with Touma at his school with Maika replying that being a top-class maid isn't easy. Suddenly, Stiyl Magnus appears simulating an abduction in order to force Touma to get out of Academy City.

Meanwhile Index, staying at Hakumeiza, discusses with Stiyl about the situation concerning the Amakusa Christians and the grimoire named Liber AL vel Legis with the the first suspected to have kidnapped Orsola Aquinas and the Book of the Law to achieve ultimate power. Then, Roman Catholic Church assault team leader, Agnese Sanctis, arrives to join the talk.

Soon as Touma arrives at Hakumeiza along with Orsola Aquinas, the latter is kidnapped once again by the Amakusa Church. But Index suggest there is no need to hurry, as Index judges that Agnese still has little information regarding the Amakusa and suggests that they might use "miniaturized pilgrimage"—a magical transportation technique based on a certain map—to escape their pursuers. Despite this, Index assures that it can only be done at midnight, meaning that they still have four hours to prepare. Meanwhile, she uses the GPS function in Touma's phone to plot the location of the nearest portal. Index warns Agnese about the possibility of escape once the portal activates at midnight, and Agnese responds by reminding them to flee the scene when they fail to retrieve Orsola by five minutes before midnight. Agnese's forces and her group along with Touma and Stiyl go their separate ways.

For the meantime, they can only rest until the time comes.

Tree Diagram Remnant Arc
Index is often seen with Touma during this arc, she first appears with Touma wondering about the weather and how it was inaccurate. She later reappears when Misaka 10032 decided to ask Touma for help to stop the Awaki Musujime. Index is last seen with Touma in the hospital in the aftermath of the arc, where she lectures Touma of trying to act cool even though he didn't resolve anything (since Accelerator destroyed the Remnant as well as beating up Awaki).

Daihaisei Festival Arc
Index wonders around the city looking for Touma, eventually coming to the first event and watching it with Mikoto. She later meets with Komoe, who convinces her to put on a cheer-leading outfit. Unfortunately, Touma walks in as she was getting her underwear on. Naturally, she tries to bite him, only to miss and kiss him on the cheek, which causes her to become frozen with embarrassment. She is kept in the dark about Oriana Thompson as it would put her in great danger, which she wasn't happy about at the end of the arc. Later, she visits Aisa at the hospital, and when Aisa said that it would be better for everyone if she wasn't around, Index tells her otherwise, that she was a dear friend to both her and Touma.

La Regina del Mare Adriatico Arc
Index joins Touma for a short vacation to Northern Italy. The two finally arrive in Italy and Touma is trying to find the hotel they'd be staying at. Index shares a little bit of Italian history with Touma which makes him surprised that she knows things outside of magic due to the grimoires inside her head. This however upsets Index and was on the verge of biting him but she stopped because she wants to have a good time, but Touma with his usual poor choice of words further infuriates her prompting the annual punishment that he's accustomed too. Later Touma loses Index because she's too busy looking at the food stalls and restaurants in the area. Index is later found by Orsola Aquinas and takes her to her house where the Amakusa Christians are helping her move.

At Orsola's apartment Index is carrying a box of gelato and Touma berates her for separating from him and getting lost but she doesn't listen. Orsola asks Touma and Index to help clean the apartment with her and they both agree too, during the cleaning Index and Orsola ends up getting dusty so they decide to take a quick shower to clean their skins. Touma on the other hand is too busy trying to fight the temptation of walking in and avoid getting bitten by Index, during that time he hears a noise from another room and he goes to investigate it. It was there that both Index and Orsola come out of the bathroom naked and it turns out that the noise that Touma heard came from separate bathroom that Orsola and Index were using respectively. Touma tells the obviously embarrassed Index that he has no intention or interest at peeking at her naked body but Index takes his comment as an insult resulting in her giving him the usual punishment. Soon after, Orsola begins to move her luggage as she prepares to leave for England, when an assassination attempt happened, where a man wearing Roman Catholic Robes tried to kill Orsola but failed due to Touma. Taking a bizarre twist, the two fall into a river only to land on some large ice-like ship that was submerged before, and it sped off towards the sea with Orsola and Touma aboard, leaving Index behind.

Index later gets help from the Amakusa Christians, who later fish out Touma, Orsola, Lucia, and Angelene out of the water after the ice ship they were on was attacked by the other ice ships. Back on land, the Amakusas are eating dinner at Orsolas house alongside Touma, Index, and the two nuns, before proceeding to plans to rescue Agnese. Based on the information from Angelene and Lucia, the fleet is led by Bishop Biagio Busoni, and the purpose of Queen of the Adriatic Sea (the name of the fleet of similar ice shops) was to cast a spell that would destroy Venezia, the land as well as the pieces of its culture around the world, which required Agnese. Yet the effects of using her to cast the spell would render her to lose her mind, something Touma refuses to let happen. Humorously, Itsuwa offers Touma a napkin during the dinner, causing Index to be somewhat jealous of the seemingly closeness between the two. Moving on, the battle plan was to create a massive amount of paper ships, and use them as unmanned suicide bombers to distract the fleet while Touma and the others board the ship stealthily. The fleet notices this plan, and opens fire on a ship that was submerged below them, only to find out the submerged ship was a decoy, and Touma and the rest of them were aboard one of the suicide ships that flew towards them.

Touma, Index, and Orsola get on the main ship of the fleet where Agnese is being held, and after being split up and having to off thirty ice golems. Index later manages to get rid or escape from the ice golems, and is later reunited with Touma in an Italian hospital. They are then forced to return to Academy City after a single day in Italy, via a Supersonic Passenger Plane. Both Touma and Index would later have a bad impression on the plane.

Academy City Invasion Arc
August 31.

Lying on the floor of Touma's room and complaining of hunger, Index makes her displeasure known. Touma tells her the menu will be soumen and noodles, but she starts to complain about that too. Then, when Tsuchimikado calls them to share the food Maika has just made for him, she rushes to Tsuchimikado's room along with Touma. Touma and Index are then seen to devour the food.

Later, Index tries to look for Touma in the city but ends up becoming hungry. Accelerator later finds her, not knowing her connection with Touma, and even treats her with food - costing him all of his pocket money. They separate as Index spots Touma amongst a crowd and runs towards him, just as Last Order runs to Accelerator. She later berates Touma and then realizes that she has yet to return the tissue pack that the stranger she met, Accelerator, gave to her, leading her to go out on her own to find him, much to Touma's chagrin.

Index later comes upon Accelerator again while he is being beat up by Kihara Amata and surrounded by Hound Dogs, what's worse is that Vento of the Front's invasion of Academy City had just taken place. Distracted by Index's arrival, Accelerator uses the opportunity to allow him and Index to escape using one of the Hound Dog's vans. Amata tries to attack them with rocket launcher but is interrupted by Vento of the Front's arrival, whom wants to kill Index as well. Accelerator, considering Index dead weight, decides to drop Index off at the hospital where Heaven Canceller works, misleading her into thinking he needed a replacement battery for his choker electrode and having her fetch it (no replacement exists). There, she informs Heaven Canceller of what Accelerator told her and later falls asleep while waiting.

She is not seen again until after Kazakiri Hyouka is transformed into Fuse KAZAKIRI, forcing her outside as she recognizes her wings of light from the distance. Mikoto tries to stop her, at which point they are then reunited with Kamijou Touma. Index pleads to Touma not to destroy Hyouka, the angel he was going to stop, surprising her. Mikoto asks what that thing is to them and Index tells Mikoto that it's a friend and that they are on their way to rescue her. A few Hound Dog members spot and attack the three, but Mikoto decides to stay behind and hold them off. With the penalty game still being active, Mikoto orders Touma to stay alive and help his friend, and although he's reluctant to leave her, he obeys Mikoto's command. While running, Index asks Touma why the streets are empty, to which Touma tells about Vento of the Front. Here, Index explains to Touma the intricacies of how her power works and how it makes people faint. Later, realizing that Hyouka becoming an angel is related to AIM, Touma then contacts Mikoto to have her help Index regarding the matter. Here, Touma and Index once again split ways, with Touma going directly to Hyouka while Index go to the core where the change was forced on Hyouka.

Index later comes upon the building where Last Order is being used as the core that allows Fuse KAZAKIRI to happen. There, she also finds both Amata and Accelerator fighting, to which Index tries to help Accelerator by throwing a phone at Amata, though he is unperturbed. However, Amata is completely preoccupied by Accelerator to do anything about Index. Index determines that Last Order is the core of Kazakiri Hyouka's angelic form and compares the manifestation of Fuse=KAZAKIRI as forcing telesma into a container with human form, similar to what the Hermetic Order of the Golden Dawn used to do. She asks Mikoto (who is still fighting the Hound Dogs) regarding science side topics such as the Brain-wave networks as well as the AIM Diffusion field in Academy City. Index determines through their combined knowledge that Last Order's mind is being restrained in order for her to become the core of the mysterious power that the city has (AIM diffusion field) and to distort it to create an angel.

With this Index need only to remove the knot that is restraining Last Order's mind so to speak. Index concludes that a song would be the apt choice, as a song's rhythm, pitch and musical intervals can create multiple interactions with the mind and incite a multitude of emotions from a person. With this she could free Last Order from the shackles that restrain her mind, and save Hyouka and all of Academy City.

At the same time as this, Accelerator, in the brink of death, sprouts black wings and finally defeats Kihara Amata. With Index singing her Aria for Last Order, she fulfills her mission as after Touma's confrontation with Acqua of the Back, Hyouka's wings start slowly disappearing one-by-one. Index leaves Accelerator to call help for him, but not before stating that the black wings that appeared were similar to telesma.

Index later meets up with Hyouka after the end of the arc just before she disappears again.

Acqua of the Back Arc
Index is initially distressed that Touma has brought home yet another girl, however Itsuwa could quickly gain Index's heart using her excellent culinary skills. Touma, however; inspired by Itsuwa's usefulness when it comes to house work, removes her from being near Itsuwa as she was bothering her, and profusely requests the technologically challenged Index to clean the house bathtub heater (an electrical heater), Index used the knowledge of "detergent is what makes everything clean" and stuffed detergent inside the machine, effectively ruining the device. Afterwards, Index goes with Itsuwa and Touma to the Spa Resort Serene Springs, where she meets Misaka Mikoto and has a little quick exchange until Mikoto faints from overusing the bath. Later, after Kamijou Touma is injured by Acqua's attack, Index stays next to Touma after he is interned in the hospital. At the behest of Touma, Itsuwa kept the actual events of this arc as a secret to Index; and as such she didn't know who Touma was actually fighting until the very end, a fact that she used to scold Touma; along with his night time escapade from the hospital.

After the end of the battle against Acqua of the Back, Itsuwa is by Touma's side. Touma awakes to find her. She tells Touma that it is only normal for him to be unable to move after all that he had went through. Here, Itsuwa says that Aqua of the Back is still alive and retreated, as well as there being no casualties in the Amakusa or even among civilians. Touma then shows his nonchalance regarding the matter, saying that it was amazing that they managed to beat him, a member of God's Right Seat and a Saint. Itsuwa is surprised by this from someone who contributed the most, despite her being the key to his defeat using the Saint Destroyer, as they have not only beaten him but did not have a single casualty. Touma tries to get out of bed again, needing to go to school, but Itsuwa stops him by pushing him down and making her face close to his, making her blush. Suddenly, Index comes around, angry at him for having Itsuwa sit beside him instead of her as well as not yet apologizing for leaving the hospital on his own. Itsuwa joins the fray, asking why he ran over to where Acqua of the Back was despite his condition. Hearing Acqua of the Back's name, Index becomes even angrier at Touma for facing such a powerful foe without consulting her for help. Needless to say, Touma is distraught over their double team. Kaori then arrives, after much prodding by Motoharu, dress in the fallen ero angel maid outfit, barging into Touma's room, where he sees his "third angel" (referring to Kaori in her outfit) after Misha Kreutzev and Kazakiri Hyouka, though he is referred to as feeling fear upon seeing it from that point onward.

In the epilogue Fiamma of the Right states his intention of going after Index.

British Royal Family Arc
When Touma returns to the dorm after his school day finished, he and Index try to enjoy their evening before dinner trying out Touma's kotatsu. Touma later gets a call from Motoharu that he and Index need to go to England without explaining anything, and knocks them out using knock-out gas. The both of them as well as Sphynx, are taken to the airport with Touma's money stolen by Motoharu and exchanging it with British Pounds. With it being too late to board the last bus and train, as well as the banks being closed preventing Touma from changing his money back to Japanese Yen, Touma is forced to take Motoharu's offer. After waking up Index and Sphynx he explains the situation  to Index, and later had her change into normal clothes. Index notes that though that they are going back to her city of birth, she doesn't really feel like it is her birthplace as she has no memories from before about a year ago. Here, Touma discovers for the first time since his own memory loss that Index too has lost her memories. They later find out that Motoharu has made preparations for them to board Academy City's supersonic passenger plane, much to their horror. Seeing this, Index and Touma decide to board on a commercial flight—Sky Bus 365. Only Sphynx boarded the intended supersonic passenger plane and arrives in London before both of them.

Much of the flight has Index wondering about their food as she hasn't eaten yet, much to Touma's consternation. They are later involved in a terrorist incident, and later becomes personal to Touma after one of them tried to silence Index after she discovered him by strangling her, he becomes enraged at the captain and becomes involved in taking down the two terrorists.

After arriving in Buckingham Palace's heliport, Touma and Index enters the palace after Kaori's explanation that Touma need not worry about destroying anything magical in the palace with his Imagine Breaker. Despite this, they are still hungry as they are greeted by Knight Leader. After Touma tells him that Index is hungry, they are given scones by a maid, at which point, after discovering it is free, they gorge themselves with it. The Knight Leader, shocked at the display and the fact that they are in a hurry, asks Kaori if she can draw her sword to persuade them, to which Kaori does something much quicker, punching Touma in the stomach and dragging Index by the hand. Knight Leader later tells them that they are gathered here to discuss the recent Eurotunnel explosion, which was actually a bombing and magic is involved. They later meet Elizard and her exuberant behavior, after Knight Leader scolded her for being unprepared for the meeting. After Touma notices the Curtana Second on Elizard's person, they start a lecture regarding the purpose and power of the sword and its connection to the history of the United Kingdom. The Eurotunnel bombing meeting in Buckingham Palace is conducted afterwards, Touma is one of the least vocal of the group that have gathered there, though is still able to speak more than even Villian. He opens up on how he thinks the meeting has something to do with Sky Bus 365 as the terrorists were French, which later leads to the discussion on the growing suspicions of the country regarding France. Meanwhile, Elizard asks Index to analyze the papers she has regarding the magic that was used to interfere with the illusion cast by Necessarius on Sky Bus 365, leading Index to say that it was Norse magic and that the magician is a girl.

When it was time for Index and Touma to split ways, with the former going to Folkestone in order to go to the Eurotunnel to analyze the magic there, Carissa tells Touma he can't follow. She says that Touma's Imagine Breaker may interfere with the investigation. Index and Kaori allays her concerns and tells him that he really doesn't need to do anything, with Elizard saying that he can do anything he wants until the situation is resolved. Touma, however is insistent in helping to keep England's peace, forcing them to acquiesce to his request.

British Halloween
As the British Halloween takes place, Index is accompanied by Carissa and Knight Leader in the Eurotunnel near the collapse portion of the tunnel. Here, Index determines that the magic used is of Roman Catholic origin and references French royalty's passing relation to it. Hearing Index's analysis that a spell related to the French royal family was used, Carissa now determines that the one at fault is a French Roman Catholic faction. Despite Index saying that the spell's used it doesn't necessarily mean that the current political power used it since the French monarchy has been ended, Carissa is adamant, pointing out that the brains behind the current political power in France have the knowledge of the historical kings of France and treasures from the royal palace. With a smile, Carissa congratulates Index for giving her the answer she wanted to hear, that France was at fault for the bombing, as otherwise she would have killed her, putting Index on guard. Knight Leader comes near and hands her the Curtana Original from the case.

Using Index's analysis as justification, now as the new sovereign of the country, Carissa orders the Knight Leader to have the Knights of England to force the military to send a destroyer to Dover Strait, and from there threaten Versailles, destroying it depending on France's answer. The Knight Leader asks if they should notify Academy City, their ally, to which Carissa's says to ignore them, threatening the connection that was established by Academy City and the Anglican Church. The Knight Leader asks if targeting Versailles is the best idea as the current political power of France is controlled in the shadows who have no permanent base, to which Carissa says that it is only because the greatest of them all is hiding in Versailles, and killing her would force the others out of hiding. Carissa orders the use of Bunker Cluster warheads. She says she will disregard the treaty that they signed to ban it with the nations of the EU as well as other unnecessary treaties. Carissa also states that she intends to cut America's economic backing to further her desire for the United Kingdom to become more independent from her neighbors. Knight Leader warns that isolating themselves after the Eurotunnel bombing and the hijacking straining the nation could make it worse. Carissa however says that all they need to do is remove the Roman Catholic Church's control from Europe, creating a structure that centered around England, solving the problems with the economy and resources, a society where England is needed by the rest of the world. Carissa comments that her mother's pacifism doesn't work in times of war and that they need to win the upcoming war without any cooperation and interference from others. Accepting, the Knight Leader begins preparations for the destroyer. Carissa comments on how she wishes that they have developed nuclear bombs, prompting the Knight Leader to say that they should use something that would not be harmful to people after the Palace of Versailles has been hit. Carissa laughs at this and says that they can send a warning beforehand as the woman they are after won't leave the palace even if they did. Carissa, still needing Index to legitimize their threat against France, then orders the Knight Leader to "put her to sleep". The Knight Leader then knocks Index out with a single punch.

Index is kept in a carriage unconscious during the Battle of Folkestone until she is rescued by Acqua of the Back. Touma later arrives and after a discussion with Acqua of the Back and encounter with Carissa, stays with her. Index later wakes up and both she and Touma are later found by Amakusa Christian scouts, and later bring them back to their temporary hideout in Folkestone, a large rescue seaplane. As it takes off for the London, Tatemiya Saiji and Kanzaki Kaori report on the current situation regarding Carissa and her frail relationship with the knights now that the Knight Leader has been defeated. They tell him of the reason for her returning to Buckingham Palace as so she can suppress the tremendous power of the Curtana Original, and that they need him, Index, and Villian to do a mission under the Buckingham Palace and force the Curtana Original to overload and weaken Carissa, allowing for the forces of the Anglican Church to mount a counterattack against her. With Index's instructions and Villian's driving, Touma's party easily bypasses the knight's magic after discovering that Carissa had London's security cameras deactivated. After coming near Buckingham Palace, the group disembarks on foot following Index's lead, eventually arriving at a subway station. With a little help from Mikoto and Villian's servants, Villian is able to use the spell against the barrier, which have been modified with the help of Index in order for her to chant it quickly, ending with Touma destroying it. With the branching railway open, the special car begins moving towards Buckingham Palace. Touma and the others later leave as Curtana is overloaded.

The group later rendezvous with the Anglican Church forces in the outskirts of London. During the "Last Supper", Index has her fill of food, even stealing from Angelene. She later meets a nun from the Anglican Church named Rachel, who says they used to play together, though Index has no recollection of her as her memories have been erased. Seeing that Index is still so cute, Rachel offers her food, as do others, eventually making Index say for the first time that she has had enough food.

In the Battle of Buckingham Palace, Index is separated from Touma, and is instead carried by Kanzaki Kaori during Carissa's counterattack on their assault using Curtana Original's dimensional debris. Index arrives after Kaori went on a short detour to save civilians from the debris, just in time to save Touma who was in dire straits facing Carissa. There, Kaori asks Index to analyze the Curtana Original, while she and the others fight Carissa. For much of the battle, Index continues to analyze the Curtana Original while as the same time assisting using her Spell Intercept. It is her combo with Villian that allowed them to give an actual blow on Carissa, who hitherto dominated the battle despite the numerical superiority of the Anglican Church forces. Despite this, Carissa orders the firing of a Bunker Cluster cruise missile on the palace. Thanks to Kaori's quick thinking, she is able to make a defensive barrier over their area, though not all of it is covered and some of the explosive shells get through, eventually destroying the palace itself. Index is not seen until later, after Elizard uses the Union Jack spiritual item and distributes the power of the Curtana Original to the citizens of the United Kingdom. Here, Index admires the skill of Elizard's magic, who uses her communication spell to have the people of the United Kingdom people in their own interpretations of the power of Curtana they are receiving in order for them to properly use them without discovering that it is magic. Index wonders if the purpose of her creation was to support Elizard, As Carissa's defense breaks down in the onslaught of the "heroes" and the forces that oppose her present due to the fact that she was trying to prevent power from her sword to be completely drained, an opening for Touma arrives after Index finally finishes analyzing the sword and uses Spell Intercept on it. Touma calls out to Acqua of the Back, and without a word, knew what Touma was planning. Acqua of the Back catapults Touma toward Carissa using his sword, Ascalon, and from there destroys the sword and then punches Carissa in the face.

When Fiamma of the Right appears to steal John's Pen remote control from the ruins of Buckingham Palace, he activates it as a demonstration, forcibly putting Index into John's Pen mode. He tries to have her attack Touma and Carissa, though finds out that it is damaged, due to its battle with Touma and damaging its "Collar". Though dismayed, Fiamma of the Right is unperturbed. He reveals he was after the knowledge of the 103,000 grimoires held within Index, something that the remote control allows him to access. Index later falls unconscious after Fiamma of the Right leaves. Elizard later takes Index's body and promises to heal her on their end, though warns Touma that so long as Fiamma of the Right has the remote Index is still in danger. The events of Fiamma of the Right's actions would later force Touma to go alone to hunt Fiamma of the Right down after asking Stiyl to keep a close watch on Index as he is privy to the ways of the Church.

World War III Arc
Index eventually learns of Touma's memory loss through Fiamma which causes her a great deal of pain. During her stay at the St. George Cathedral- the Necessarius headquarters, Index grows "Red Wings" and defeats Stiyl Magnus with ease, who tries to restrain her in vain. She succeeds in destroying the headquarters in the process.

After Touma defeats Fiamma and refuses to escape from the fortress, Index asks Touma why he didn't escape too. He told her that there were still a task to take care of. When she asked about his memory loss, he promises her that he will meet her again and apologize personally. He tells her to get Stiyl to contact him so he could control the fortress' decent, and he destroys the controller. After Touma disappears, Index asks Stiyl what happened to Touma, but no one can answer her question.

Freshmen Arc
Index is seen wandering around Academy City briefly by Accelerator while he was out grocery shopping. Accelerator noted to himself that something was different about her, like she was depressed and had fatigue and impatience.

Homecoming Arc
As she wait in the dorm room unsure what to do or how to contact Touma a heavily intoxicated Touma suddenly walks greets Index after a long period of time, along with the many other girls that appeared having been magnetically stuck together via Mikoto's power This of course leads to him being greeted with being bitten. After Touma sobers up and the other girls leave she then helps Leivinia Birdway explains the principals of the magic side to Accelerator and Hamazura Shiage.

Ichihanaran Festival Arc
Index appears at the end of the arc, asking Touma for an explanation for what he has been doing all this time. After Touma quickly sums up his experiences, she asks him who's the girl clinging on his back is, to which Touma says it is Fräulein Kreutune. Index then asks why she is clinging on his back, to which she says that she ate something strange which that was made by Cendrillon, which resulted in her shrinking. Index asks the question again, to which Touma now says that it was because she thought embracing her friends was the normal thing to do. Index doesn't get mad however, saying that he hasn't changed. However, she tells him that there is something he is supposed to say. Index sincerely says welcome back to Touma, but Touma utterly screws it up in embarrassment, to which Index bites him for his trouble.

Agitate Halation Arc
Index appears only at the end of the arc. She and Tsuchimikado Maika are walking together with Maika complaining about not getting extra credit points for cleaning an external institution and Index complaining about Touma not feeding her as always.

Magic God Othinus Arc
Touma wakes up finding Leivinia Birdway and Lessar sleeping with him in the bathtub. As he tries to escape the situation, Index finds out and proceeds to bite him.

Leivinia ends a conference call with the allied nations and says that the preparations are complete. Index thinks that she ordered a pizza, to which Leivinia replies that she would rather order sushi or soba since she is in Japan. As they are eating their breakfast, Index finishes her food quickly and demands for more, who later acquiesces after initially refusing. Leivinia explains the reason they came to Japan is because they needs Touma’s help, to which he refuses at first but then agrees after the threats and explanations from Leivinia. She then tells them the location of GREMLIN's headquarters.

Index is then asked by a sleepy Lessar if it is okay for her to let Touma go, to which Index replies that complaining can’t stop Touma. They then proceeded to go to School District 23, walking on the same path where the students go to school, making Touma feel awkward at the looks of the people passing by due to the fact that he is surrounded with foreign girls. Lessar then tells him that they will not falter when faced with alienation in that level. They then waited for a bus to District 23, and as Touma sits on the bench near the stop, Leivinia begins sitting on his lap with Lessar clinging to his arm, saying that she is still affected by jet lag. Index the becomes mad at the sight before her, and then proceeds to bite him as usual. Mikoto would later see them and in response uses her powers to rip the bench from its foundations and catapults its occupants away, though they are left unharmed by this display. Index and the others are at District 23 international airport. Lessar and Leivinia then proceeds to shop for swimsuits so as to prepare to go and hide to a resort after defeating GREMLIN since they would likely be the target by the churches after everything is finished. Leivinia and Lessar insists on going to "50% Less Skin Covered" swimsuit store, to which Touma refuses and instead suggests to put into a vote to which store to go. Touma tricks Index that "Tropical Bright Girl" sounds more delicious and thus gets her vote. Touma wins and they proceed to the other swimsuit store (Tropical Bright Girl). On their way, Mikoto then asks Index if these crazy things always happen to Touma, to which Index responds that this is just the third link of the chain. As they enter the store, Index says that she would be fine with any store as long as it has food and Touma reacts if she has finally reached the point wherein she will also eat swimsuits or cellphones as well. Index then exclaims that she can smell cafes and bread shops around. Touma is amazed at her skill when it comes to food and Index tells him that food doesn't change and as long as there is food, she will eat it. Mikoto then says to Index that she must not underestimate the advances made by science and says that even a trash meat in Academy City is much better than the average in the outside world. Index then screams at Touma, to which Touma responds that he can't afford such a high class meat. They then enter the swimsuit shop and Index says she doesn't care about swimsuits since it is November and asks Touma when they will go to eat. Index, Leivinia and Mikoto then catches Lessar, who was overcome by shock due to Touma defeating her sex appeal, and then Touma holding a swimsuit and misunderstanding the situation.

They the meet Kumokawa Maria at the airport and Index asks Touma who is this other girl that she doesn't know about. After receiving word that Sargasso has already been located, the GREMLIN invasion of Tokyo has begun as well. Touma runs off with Index and Mikoto following him. After letting Mikoto go with him, Index demands to go too, to which he agrees. Index and the others proceeded to ride an electronic cart to a supersonic passenger plane. As the plane leaves Academy City, it is sliced in half by a giant dragon. Index and the others are then mercilessly thrown out into empty air.

GREMLIN invasion of Tokyo
As Index and Mikoto are falling from the sky, Mikoto stops using her parachute and catches Index who is chaotically rotating as she fell. Mikoto then uses her electromagnetic power and lands vertically on the wall of a giant train station building while holding Index. Mikoto is dumbfounded that the place is packed with people to the point that she can't see the sidewalk. Index then tells her that it was GREMLIN's doing. Suddenly, a giant dragon flies over their heads but does attack them. Mikoto then tries to use her cellphone but it was of no avail since the lines were apparently overloaded. Mikoto then starts to move from building to building using her electromagnetism and while still holding Index. They are heading for Sargasso since Mikoto thinks that Touma will probably head there as well. While moving, Index then warns Mikoto to watch out and they land perpendicularly on the side of a high rise building. As soon as she does, countless sparks appear floating down and each spark strikes the glass wall and produces pillars of flame that took form. Index then explains that it is the Muspell from the Norse Mythology to which Mikoto doesn't understand.

While still holding Index, Mikoto uses her electromagnetism to jump from wall to wall. They were being pursued by the Muspell but they tried to escape them. Mikoto then asks Index if she knows where they are right now to which Index responds that she doesn't know. They then wonder what has happened to Touma, when suddenly they see an Academy City bomber and realize that Academy City has made their move. They also see an eagle-like creature that fly, to which Index says that it is Hræsvelgr and explains it to Mikoto. Suddenly, the creature fall toward a wide open space as it engages the Academy City bomber.

Mikoto while holding Index later saves Touma just in time before he is about to fall from a speeding train. Index is then released by Mikoto and she proceeds to scold him, to which Index says that it won't change Touma. Index then tells Touma that she would be going with him this time and she won't be backing down no matter what he says. Touma's cellphone then falls down while some button was pressed and he hears his mother's voice saying that she is fine and they don't have to worry. After hearing that, Touma then tells Index and Mikoto that the opponent he's facing now is Freyja and asks them to lend him their power so that he would be able to save both Freyja and the mother to which the two responds that he leave it to them.

Just as Freyja commands Nidhogg Vol. 02 to attack them, Mikoto attacks it using her ability and repeatedly fires railgun at it at point blank range. The dragon is stopped and Freyja is shocked at this turn of events as Mikoto is left behind. Freyja then summons more creatures. However, Index casts Spell Intercept against them. Touma then tells her to analyze the magic being used to give birth to those '"children." Touma then persuades Freyja to let Index finish the spell and help her rather than relying on the power of the magic god. Index then analyzes the spell while Touma takes care of the others that tries to interfere. While Touma rushes to his opponents, Index then mutters an incantation and everything goes back to normal. The mother is unaware of what is happening and where she is, then she falls unconscious. Index then asks Touma on what they should do now, to which Touma responds that they must ensure the safety of the pregnant woman. They later sneak on a different train and then arrive on a switchyard near the bay. They then see Leivinia, Lessar and Maria on a rubber boat and meets up with them. Mikoto also comes last and scolds Touma for leaving her behind after that bold announcement asking her to help him, as well as the fact that he is going after a pregnant woman to which Touma has to explain again due to the misunderstanding. They then try to get to the boat and leave for Sargasso. On their way, they are attacked by Nidhogg, and while they are preparing to counter it, Kagun defeats it. Maria then recognizes that it is Kagun and decides to go with him, along with the pregnant woman. Index and the others then continues on to Sargasso wherein they are met by Mokkerkalfe, but it is destroyed by Thor (Ollerus in disguise), allowing them to continue.

They later bear witness to Othinus becoming a perfect Magic God, due in part to the efforts of Ollerus and Fiamma of the Right not knowing that she need only to fail or succeed 100% to unify her infinite possibilities to become a magic god. Moreover, they later see the result of their failure, Othinus summoning Gungnir from her eye socket. They are left behind by Touma as he desperately tries to charge towards her, but all is in vain and the world is later destroyed.

Shifting and Fluctuating World
Prior to Touma accepting that the cruel worlds he is visiting is actually reality, he frequently calls out to his comrades that followed him to Sargasso, Index, Mikoto, Leivinia, and Lessar.

In the second recreation of the world by Othinus, known as the Version_Beta world in-text, where another "Kamijou Touma" exists living Touma's life. She comes to a certain high school to complain about her lunch to "Touma". Later "Touma", and Index come upon Seria and Maria as they are riding a bike. After much arguing, Index slams the breaks and catapults "Touma" out of the bike. This eventually leads to "Touma" falling between Maria's legs, much to both Seria and Index's chagrin. Maria tries to explain to Seria on how she is fine with it because she wears panties for her abilities. As "Touma" is in danger of being bitten by Index, he gives Maria a piggyback ride, his head between her thighs in order to stay Index biting him, knowing that she only bites him. Maria naturally cries out as he does so, and gathered strength in her thighs to keep her balance, annoying her sister Seria. "Touma" tells Index to calm down or else he won't put Maria down while they shop, though Maria as well doesn't want to be piggybacked either while they're shopping. Index agrees with him, stating that she will have to master some techniques using her arms and legs, much to "Touma's" horror. Seria then mentions on how Maria is grinning a little bit, and casting aside her cool and intellectual demeanor, screams and dropkicks on "Touma's" back. He falls, but Maria manages to land safely. He later ends up in Index's skirt, to which she tells him to prepare himself for some pain. Both Maria and Seria attack him as well afterwards. When “Touma” and Index get to the underground department stores seeing the price tags that he came back to his senses and attempted to suggest that instead they get an economical oden pack at the supermarket or convenience store. Index claims that she's already seen the best one and that by turning back now her desire will never disappear. “Touma” tries to dismiss this but stops when Index snaps her teeth together in a mensing warning like some kind of trap.

In the final recreation of the world by Othinus created specifically to break Touma's spirit, known as the Version_Omega world in-text, where several characters from the original world have been "saved" or have not experienced great tragedy, the cruel fate that made Index forget Stiyl Magnus and Kanzaki Kaori and forced them to pretend to be her enemies have apparently not transpired. Index, Stiyl, and Kaori, along with other priests and nuns presumably from the Anglican Church, first appears in the park where Othinus puts Touma after recreating the world. Touma, already at the precipice of despair after seeing the "perfect world" and his continued conversation with his tormenter, is stunned by what he sees. Index is happily playing with Kaori and Stiyl with a soccer ball, which later finds its way before Touma. He instinctively try to reach towards Index's ball, and there Touma realizes that this "perfect world" is the future where they had not failed and had not had their role stolen by Touma. Index grabs the ball, and before turning away she sees Touma, whose suffering is likely written all over his countenance. She asks him what's wrong and if his stomach hurts. Touma is tempted to use his right hand and reach out to her, to check if something would change if he touched her. Touma's hand trembles, but manages to form smile and say to Index that he is fine. Index then jogs away back to her group, unaware to the great torment that is befallen of Touma.

Later, after Touma's spirit has been finally broken and is trying to decide on how he should have himself killed, he wanders around a festival, seeing several familiar faces smiling. Here he has come to the conclusion that the smiles of the people in the perfect world Othinus truly held weight and his decision to kill himself had meaning. Then he hears Index's voice and sees her figure carrying Sphynx running towards his direction. She is apparently trying to catch up to Stiyl and Kaori, telling them that it is wrong to only her choose three things in the festival for food as she is starving. Seeing her, Touma burns the scene into his mind as she runs pass by him. Touma hears voices behind him, but he does turn to look back, and had felt he has seen what he truly needed to protect. And thus Kamijou Touma with the weight of all the world's smile bearing down upon his broken hearts continued forward and onwards toward a singular tower that loomed above him, finally deciding the way he should end his life to protect the cruel perfect world.

After Othinus concedes the world to Touma, she recreates his original world using the Imagine Breaker. The group that went to Sargasso with Touma are back as well, unaware of what had transpired, and are about to face Othinus immediately after her confrontation with Touma in the Black World. With Othinus having lost Gungnir to Touma, she faces her fate in Touma's world. Index calls out to her, telling her that they won't let her get away with what she had done. Mikoto then speaks up, saying she won't hold back after Othinus got her mother involved. Lessar speaks as well, complaining about her and GREMLIN causing chaos. Finally, Leivinia says that she should be crushed right away otherwise she would go hide somewhere and cause problems later. The group later attacks Othinus with Touma still dumbfounded with Othinus' decision to bring him and his world back, causing her to be knocked backwards. Finally, after Touma asks Othinus if she knew of her fate when she saved him, the girls with him are surprised by his outburst. Touma later runs toward Othinus, all the while they try to call towards him. The group later witness Touma defending Othinus from the attack of the Anti-GREMLIN Alliance using magic missiles.

VS the World
Immediately after stopping the international coalition's magic attack on Othinus and declaring his intention on saving her even at the cost of making the world his enemy, Touma and Othinus spirits away from the group and vanish.

Index, Mikoto, Leivinia, and Lessar are flabbergasted by what happened as they are completely ignorant of what had transpired in the many worlds of suffering that Othinus created to break Touma's heart. With Touma and Othinus gone, they start forming conjectures of why Touma made a complete 180 the moment he arrived in Sargasso. Leivinia assumes that Othinus may have messed with him as she is a magic god, though they actually don't know what she can or can't do. In the meanwhile, Index keeps quiet as she contemplates the likelihood on what had happened, for she has 103,000 grimoires and from her position could predict what a magic god was and a magic god coud do.

Leivinia says that in any case they must get Touma away from Othinus for though he is somewhat special he will be danger when the coalition army attacked and get caught in the crossfire. Lessar however takes this chance in teasing Leivinia, saying that she may be upset that someone took her "big brother" from him. While they are all preoccupied with themselves, Academy City sends out a message to all Level 5s, Mikoto included, to kill Magic God Othinus and Kamijou Touma.

Mikoto and Lessar later leave to deal the situation regarding Touma on their own. However, Leivinia and Index joined forces to construct their own lance, under the rationale that only a phenomenon extracted from a magic god can kill a magic god. Moreover, Index divulges to Leivinia what might have happened between Touma and Othinus: that she had become a complete magic god and that she and Touma fought somewhere. Still however, they could not grasp what had transpired between them.

Later, at the height of the manhunt for them as Touma and Othinus try to cross the bridge leading to Funen, they are met by Leivinia and Index. Leivinia says to Touma that she will not bother with questions she will defeat them and restrain them as quickly as possible since they consider Othinus as a threat under their rules and already assumes a battle stance. Touma then tells them if he needs to explain it all over again since he already settled it all to Mikoto. Leivinia and Index suddenly comes to a stop after hearing Touma say that. Touma then tells them that they just have to call Mikoto to explain things so that they don’t need to fight making both Leivinia and Index mad. Leivinia then says that they have the slightest idea on what happened to them back then and she is planning to go easy on Touma and take over for him but what he just said made her mad so they proceed on fighting him.

While on their battle stance, Leivinia tells Othinus that she can fight too if she wants then a moment later, a smaller replica of Gungnir appeared from her hand. Both Touma and Othinus are shocked as when they saw it. Leivinia then explains to them that the 103,000 grimoires contain the possibility of reaching the level of a magic god if used right. Moreover, she tells them that she made some modifications for it to be fit for human use and just produce the same phenomenon as the thrown lance which can be only used once but have enough power to kill a magic god. Knowing the power of Gungnir first hand, Touma warns her that it is not the convenient tool she thinks it is. In spite of this, Leivinia is still adamant with her decision and is making use of all the 103,000 grimoires. Because of this however, the “poisonous knowledge” of the grimoires flowing from Index continually contaminate her mind resulting in headache for her, but she tries to suppress it.

As Leivinia is about to throw the lance, Touma charges forward but dashes right pass her. It turns out that Touma figured out that Index provided the knowledge through her singing and tries to stop her. Touma successfully stops Index, though not the way he intended, as he gropes her chest, startling her and interrupting her singing. The lance then becomes unstable in Leivinia’s grip, resulting in it exploding. Touma is then bitten by Index as punishment. Index then nags on Touma for his lack of delicacy. As both Leivinia and Touma later lie face down on the ground while Othinus pokes on him. Touma asks Leivinia regarding how much they know about what happened to both Touma and Othinus. Leivinia responds by saying a complete magic god won’t bother with mere physical attacks but rather proceed on remaking the world. She then asks Touma on what did he saw in the changed world in which Touma said that nothing much but he learned something very basic which leads him on deciding to save Othinus and that he would never choose to kill a “mere girl” and smile about it. Leivina then responds that he is exactly the kind of person he is and that she is like an idiot worrying about the fate of the world and whether information was leaked to GREMLIN by him. Touma then stands up about to go on their way when Index tries to stop him, still not finished with her scolding, but Leivinia holds her down. She then asks Touma on how he is going to settle it to which Touma responds that he will neutralize Othinus’s power then hand her to America. She then asks Touma if there is a way to do that and Touma says that if there is none, he would have been broken long ago. And so, Leivinia decides to hold down Index since if she comes with him, Index would perfectly memorize the trump card in defeating a magic god and thus the threat around her would rise to the next level. Touma then asks Leivinia to look after Index to which she agrees.

After the events that have transpired in Denmark, Touma is put back in his usual room in a certain hospital. After, the Heaven Canceller declares that it is now okay for visitors to enter, Index comes in with Sphynx. Index demands a show of gratitude or an apology. Touma says that he wold love to bow down to her in apology but he can't do it because he can't move. Index becomes worried after seeing the bandages covering him and asks if he is okay, to which Touma says that he is. He tells Index however, that he couldn't do anything about Othinus and thinks that the cracks that have appeared on her body have already too far spread by the time she rejected being saved. He says that no matter he did his right hand, it wouldn't have changed the result.

Index tries to speak but Touma continues talking. He asks what it even means to save someone. He recalls her smile just before she fell to pieces and that she told him that she was already saved. He couldn't understand Othinus' smile and he truly did save her as his actions contradicted with what she wanted. He says that he may have been presumptuous to think he could save someone, but says that all he wanted was to see her smile in a different way. He contemplates on how it may have been his own selfishness or maybe his personal views as good or bad. Regardless, Touma believes Othinus vanished from the world and bitter feeling comes upon him and the only thing he could do is to accept the fact and continue on.

However, the both of them later discover that Othinus is still alive, though only 15 centimeters tall. He berates Touma for acting that she is dead. Touma is confused, but tells him that he was part of the reason why. She tells him that since she had yet to put her eye back in she was essentially still a magic god and not human. As such, she was not completely destroyed as she was unable to fire the final crossbow show on Touma when he destroyed the fairy spell with the Imagine Breaker. And since she was a magic god and not a human, it crumbling is not enough to kill her. Touma is dumbfounded and so was Index as her grimoires only had the knowledge needed to make a magic god out of a human and not what happens afterwards. Othinus tells Touma that at this point, Magic God Othinus has been 99% destroyed and the remaining pieces have gathered on their own, though her form has changed and that she can no longer use her former power. Little did Touma know that Othinus questioned herself if her body would "automatically" re-form had it not been for the intervention of her will.

Touma then asks if he can touch her with his right hand, to which he tries to do so, much to Othinus' embarrassment. Index is enraged as well as she snaps her teeth. Touma explains that with people like Kazakiri Hyouka she wants to avoid having her vanish if he touches her with his right hand. Othinus tells her that there should be no problem in him touching her as she is now a neutral magic god, but she can't say for sure since they haven't tested it, but says that her basic properties shouldn't have changed after she became smaller. It was only after that Touma truly realized that Othinus has revived and has returned to him, and was unsure what expression he should make. Touma then asks why she wasn't taken in by America and imprisoned. Othinus tries to explain but before she can do so, Sphynx jumps off of Index and onto the bed towards Othinus, surprising her. Othinus asks for help, but Touma says he is unable to do so in his current condition. As she is held in Sphynx's mouth, Othinus recalls what had transpired after she became small and after Touma finally collapsed back in Denmark. She is given punishment by both Roberto Katze and Queen Elizard for the special circumstances that had surround her, and that is she must forever watch the world's happiness that she went as far away as suicide to look away from, an ironic fate, given that this is the same fate she subjected Touma in the Perfect World. And so, Othinus must bear the greatest punishment humanity can give to her after achieving victory over a magic god.

Mental Out Arc
Index and Othinus becomes angry at Touma for removing his cast, with the former threatening to bite him and the latter threatening to jab him in the eyes and ears.

St. Germain Arc
Index, with Sphynx, joins Touma and Othinus go to Dianoid, as the latter wants to buy a dollhouse for protection against Sphynx. Here, Index shows some antagonism with Othinus when she disagrees with her. Later, due to Touma and Index's careless words, Othinus runs away believing she won't get her dollhouse. Index later sets Sphynx loose to track her down, much to Touma's chagrin. Index's actions don't help him as he also loses Index as well in the process.

Index and Othinus later find Touma after his first encounter with St. Germain. As Touma did not know St. Germain's name as well as believing his lies, they are oblivious to the fact that Touma encountered a fake and not a true magic god. Nevertheless, Othinus confirms to Touma that in theory other magic gods should exist, though she says it is unlikely as they should have already interfered. In the end Touma still believes St. Germain's lies that he is a magic god. Though afraid of once again facing a magic god, Touma determines to stop them. He asks Othinus how to kill a magic god, to which she says Ollerus' Fairy Spell could be modified to kill one. He later asks both Index and Othinus to help him. Touma tasks Index to analyze St. Germain as much as possible, while Othinus was to go with Touma in order to determine if he truly was a magic god.

Touma later sees Hamazura Shiage on television encountering St. Germain. Abandoning his plans, Touma uses the large water pipes of the Dianoid to get to him as quickly as possible, believing him to be in grave danger. Othinus hitches a ride on Touma without his knowledge, leaving Index alone. Despite this, Othinus is fully aware later that she needs Index in order to form a countermeasure against the framework that makes up St. Germain after she finishes her analysis on them.

As the battles against the St. Germains comes to pass, Othinus meets Index and Sphynx again in the air ducts. Othinus tells Index that they need to go to the lowest level where St. Germain is and where Touma will be. Crawling inside the air ducts they then find themselves at their destination. They observe the St. Germains and Kanou Shinka with the "Queen Anne's Shield", where both Index and Othinus ascertain that it is definitely a fake made up by St. Germain, though as it is magic it is still dangerous for Shinka, who is an esper. Here, Othinus believes that St. Germain wants to break Touma's heart by having his opponent, Shinka, die in front of him.

After Shinka decides to fight St. Germain, Othinus and Index later come out of the air duct as one of the many people who has come to stop St. Germain. As the others fight with the St. Germains, Index and Othinus analyze one of their knocked out bodies. As Index slowly unravels the true nature behind how St. Germain works through her singing, Othinus is there to stop her from being deceived by another one of St. Germain's lies. With that, Index begins her work in deleting the structure that the St. Germain framework is made of, leading to them finally being defeated after Shinka does the finishing blow.

World Rejecter Arc
When Nephthys arrived at the Kamijou Residence seeking shelter, Index tried to bite Touma, angered at the thought of more freeloaders and therefore less food for her. After evading her, Touma discovered that the fridge was nearly empty despite him stocking up at a sale three days previously and confronted her about it. Once Nephthys had explained about Kamisato Kakeru and the World Rejecter, Index was left to take care of the place while Touma went out to the shops to buy ingredients for dinner.

After Touma and Othinus returned from the shopping expedition with no food and Leivinia Birdway, Index carried out an analysis of the magic that was being applied, identifying a hybrid technique using legends from the. As she identified the cannibalization aspect, Leivinia woke up and made a comment which led the two into a brief bust-related scuffle before Leivinia explained her circumstances and her situation which had befallen her sister Patricia Birdway. As the night wore on, Index became increasingly upset at the lack of food, bursting into tears when Nephpthys accidentally turned the TV on to an advert for fried chicken, and lunging when Touma was checking if he still had a fish sausage from a trade at school.

As the Kamisato Faction began their attack on the dormitory, Index was entrusted with taking care of Nephthys. On Touma's instruction, Index used her Spell Intercept to interfere with Elza's magic, causing her coins to explode out of her bottle, providing enough of a distraction for Touma to reach Kakeru. Following the premature elimination of Sample Shoggoth, Index witnessed Nephthys sacrifice herself in order to save the dying Patricia. Afterwards, Touma left Othinus with her before he faced Kakeru.

Salome Arc
On December 4th, Index was eager for breakfast and apparently going nuts with Sphynx before Touma got up. Cutting bread with plastic cutlery and glittering eyes, she remarked on how eating something sweet first thing in the morning made her feel a bit like a bad girl, to which Touma replied that she likes everything so he couldn't exactly go on what she thinks.

The next day, while having breakfast, Index remained quiet during the conversation between Touma and Othinus, before mentioning how she had been waiting a normal meal for a while, but now that she was having it, she was finding it so normal it was boring.

Element Arc
During the abnormal December heatwave and the emergence of the Elements, Index, Othinus and Sphynx were allowed shelter at A Certain Middle-High School. On December 7th, when Touma visited them on the school's rooftop, Index was helping out by constructing a glider based on Fukiyose Seiri's instructions, using old-fashioned carpentry tools. Happy to see Touma, Index noticed his bandages and ask if he had been hurt again. On being asked what she was building, Index proudly replied that it was a secret weapon to make his fight easier, before being complimented by Fukiyose for her work and being a quick learner.

Kamisato Rescue Arc
On December 9th, Index and Othinus were sent a message by Touma, who sought their help regarding the issue of Kamisato Kakeru, who had been exiled to the 'new world' and was being used by Yuiitsu to force the Kamisato Faction to hunt Touma down. They went to meet him at noon at District 7's station plaza, however the presence of the Kamisato Faction forced Touma to abandon the plan and avoid meeting up with them.

As the '48 Hours to Restore Order' came to an end, Touma returned to the school and was bitten by both of them for standing them up.

Aleister Crowley Arc
On December 11th, Index, Touma and Othinus accompanied the Tsuchikimados and Karasuma Fran during their attempt to escape the city and the subsequent ascent through the Windowless Building.

Toaru Kagaku no Railgun
Index only makes a small appearance in Toaru Kagaku no Railgun. Apart from her brief appearance in the 2nd opening where she was seen chasing someone (Kamijou Touma), she appears in episode 17 of the anime where she met Tessou Tsuzuri during her patrol. Here, she introduces herself as a sister and not a student and is seen fighting against a cleaning robot who "ate" her donut. She later appears in episode 19 when Touma is looking for her. Her appearance in this part is somewhat obscured though she is seen eating food prepared by the Tokiwadai Dormitory for their visitors, and it is implied that she is the glutton that Tsuchimikado Maika was referring to earlier in the episode.

She is last seen in the epilogue of the last episode of the anime where she is drinking a soda with Touma.

Sisters Arc
While Touma was hospitalized, Index is seen running to the hospital and into his room.

Dream Ranker Arc
Index is seen looking for Sphynx and later finds him after he scares a crow into dropping the Indian Poker card that carried the Breast Upper in it.

Toaru Majutsu no Index: Love Letter Competition
Bundled with Rainbow Spectrum Colors, the short story focuses on Kumokawa Seria's attempts on finding out a spy, by sending out a fake love letter to be delivered to Touma during a time when he is absent. This causes a ruckus with people who are familiar to him.

Index receives the blank envelope after Hyouka delivers it to Touma's address after it has done much travel. Index opens it up to discover that the envelope is empty.

Toaru Majutsu no Index: Road to Endymion
Index supports Touma throughout the short story. She is the first one to notice the strange spell set-up around the city, and is invaluable during their attempt to save as much information regarding the cabal that has infiltrated the city as they can. She aids Touma in the final battle as she analyzes the magic that is used by Ureapaddy Exica against him.

Shinyaku Toaru Majutsu no Index SS
Index is the primary protagonist of the short story. After being given money by Touma after solving several puzzles from a reward site using his account, she is determined to buy Touma a gift that can make her happy. Here, she meets Mikoto and Kuroko, infuriating the former with her antics, reuniting with Hyouka, as well as being aided by Maika on what she should buy for Touma, ending with a steam oven to be delivered to Touma’s dorm.

She later meets an Egyptian magician named the Priestess of Bastet, who has reconstructed a specific Book of the Dead in Index using various clues that only Index can notice, and wants to extract it from her. Here, Index shows her prowess against the magician without throwing a single attack, using her Perfect Memory, her incredible fast-paced analytical abilities, and backdoor tricks that magicians use to quickly subdue her opponent. However, it is her empathy that beats the magician, as after discovering her goal, she determines that all she wanted was to know more of the person she cared for through that person’s Book of the Dead that was completed using Index. Index has her voice transform into that of the woman that the magician cared for, and ending with the magician satisfied with discovering the person’s feelings.

When Index returns, Touma asks how her day was, ignorant of her adventure and confrontation with a magician. She then says that Touma is going to be happy because his “steam” is coming to the dorm for delivery. Not knowing what she meant regarding the steam oven, Touma becomes confused.

Toaru Majutsu no Index Movie: Miracle of Endymion
Index is a central character in the movie, where she and Touma meet aspiring idol Meigo Arisa in he streets, and become fast friends. They later become embroiled in a struggle between magic and science sides wanting her. Index is later tasked on preventing the plans of Ladylee Tangleroad in coming to fruition along with Touma, as she would bring the world to destruction using the Endymion. She later comes before Ladylee, who is revealed to be 1,000 years old and is searching for a way to die, in her core room, and though she tries to convince Index as they are both "cursed by magic", Index says that she knows that Ladylee will not die using her magic. She later uses her knowledge of 103,000 grimoires to analyze and undo Ladylee's spell, who has become too weak and maddened to stop her, while Shutaura Sequenzia and Arisa merge back into one another to cause the Miracle of Endymion.

Touma later admits to Index that Arisa was not an illusion as his right hand did not destroy her, and along with him, later hears a song only the two of the could hear, believing it to be from their friend.

Toaru Majutsu no Index-tan
Toaru Majutsu no Index is subjected to J.C. Staff's parodying, like ‘’Shakugan no Shana’’, Index is turned to a miniature version of herself albeit with a strange marking on her left eye called Index-tan. In the first sketch Index-tan reenacts her meeting with Touma but is then taken away by a bird and is presumed to have been eaten. Index-tan is later seen eating on top of Touma's head a'la Shana-tan and then proceeded to imitate Shana-tan, Index-tan later urges people to buy the Shakugan no Shana DVDs. During the part where Touma insert his right hand inside Index-tan's mouth to disable the magic within her, Touma says "such misfortune" after being vomited upon by Index-tan. Finally Touma and Index-tan watch a commercial featured by Motoharu and Aogami Pierce, asking Index-tan to be quiet after her amazement.

In the second episode, Touma meets Index-tan again and instead of being taken by a bird she is taken by a cat. When Touma is waiting for Hyouka and Index-tan in a changing booth, he comments on how they are mumbling the song they are singing as to go around copyright laws. When Touma is in the hospital he is visited by Kuroko masked in black clothes (a play on Kuroko's name, as are black-wearing stagehands in traditional Japanese theatre) and Index-tan, who mistakes the antics of Touma's voice actor for his.

Index reprises her role as Index-tan in the third episode, however this time she appears as a homage to the title character of . Touma's meeting with Index is redone but with Index-tan as a squid girl, moreover, after every sketch Index-tan shouts the word "Geso" loudly, as a reference to Ika Musume's verbal tic. The second sketch with Index-tan features a parody Ouma's capture of Index, here, Index-tan makes a social commentary regarding the youth and tradition, specifically, the Bon Odori, while Ouma plays melancholy tune in his lyre (previously his Azusa Bow) before Touma arrives. The final sketch with Index-tan features her with Touma and Agnese-tan with Angelene doing cute things, while she makes derisive comments and being harmful to Touma.

Toaru Majutsu no Index (PSP game)
Index is featured as supportive character in the Toaru Majutsu no Index video game.

Toaru Majutsu no Virtual-On (game)
Index is one of the playable characters in the Toaru Majutsu no Virtual-On video game. Her associated Virtuaroid is IDX-10/3000 "BAL-RlooN".

Shakugan no Shana
In Shakugan no Shana S, one of the two of Yuji's friends was wearing a T-shirt with the face of Index on it. While another one was wearing a T-shirt with Mikoto on it.

Shakugan no Sana-tan Revenge
Index-tan makes a cameo near the end, inserting herself in one of the sketches Shana-tan performs. Here Index-tan remarks that she is hungry while Shana-tan demands Index-tan to go back to her own show, they argue on how Index-tan was only asked to appear on her show. It later pans out to one of the characters of Shakugan no Shana remarking on the appearance of Index-tan and that she is an amateur (referring to her voice actress).

Dengeki Gakuen RPG: Cross of Venus
Index is an unlockable playable character in the game. Index joins your party after you defeat a fake Stiyl Magnus in the game, unlike many of the other playable female characters in the game, Index is more of support-type character using cards that are used in the game to aid the party.

Zettai Hero Project
Index appears as a boss character in her own dungeon in the game; defeating Index allows the player character to access her costume and allows the player to change their form into that of Index, her character class is "Sister".

Disgaea 4
Index makes a small cameo appearance in the game, when the players cast the Omega Heal spell. Her appearance in Disgaea 4 is actually drawn by Haimura Kiyotaka, the illustrator of the light novel.

Lunatia
Index and Index-tan are part of the NPC characters that will assist the player in the japanese version of the Korean MMORPG Lunatia.

Lucent Heart
The Japanese Lucent Heart developed by Gamania Digital Entertainment has disclosed that Index, along with Touma and Misaka Mikoto will be added as "selectable skins" for the players to use.

Abilities
Despite normally not being able to use magic, Index has a magic name, Dedicatus545, "The dedicated lamb protects the knowledge of the strong" (献身的な子羊は強者の知識を守る). As the vessel for 103,000 magical books, she is unable to use conventional means to cast spells; instead, she can only use abilities which intercept opponents' spells.

Perfect Memory
Perfect Memory (完全記憶能力): Index is capable of perfectly memorizing anything, which is one of the reasons why she was chosen as the vessel for the 103,000 grimoires, magic books that are poisonous to the mind. This made Yamisaka Ouma wonder if Index is even human.

Not only that, but she has powerful analytical skills, able to examine a 30 fps anime easily, as well as making her able to reconstruct an image on a surface, like a balloon or bottle, even after it is destroyed.

Abilities-related to being the Index Librorum Prohibitorum
Index also has abilities that require no mana whatsoever, for they are not of magic, due to the knowledge that she has from the 103,000 grimoires inside of her. This allows her to minutely to pin-point the weaknesses in the spells of others better than anyone in active combat, and later use it against magicians, such as what happened to Angelene, and her poor usage of her magic coinbags in their first battle.

Spell Intercept
Spell Intercept (強制詠唱 (スペルインターセプト) ), it uses Notarikon codes, a quick Kabbalah reading method that uses only the first letter of a word, to hijack the spell formula that the caster has been conjuring in their head and cause the magic to go berserk or be outright cancelled. .

Singing
Singing is a fundamental part of Index's abilities. Using her knowledge she gets from the 103,000 grimoires, Index uses her songs to break down spells and things similar to them. For example, Index uses her singing to eliminate the virus that plagued Last Order's mind, which allowed the Imaginary Number District and Fuse Kazakiri to manifest in Academy City.

A specific form of singing, Sheol Fear (魔滅の声</rb> (</rp>シェオールフィア</rt>) </rp>) is an ability in the form of choir that points out and impeaches the contradiction of the basis of the religion or theory of magic that has been cast and causes a break down in the enemies mind. This can be bypassed if there are belief systems nearby, such as an Amakusa Christian near a group of Roman Catholics, or when the intended target cannot hear it, such as when the Agnese Force nuns jabbed their own ears to block off the sound.

John's Pen
John's Pen (自動書記</rb> (</rp>ヨハネのペン</rt>) </rp>) is referenced by Index as her "awakening." Here, her voice becomes machine-like and toneless. Her speech becomes blunt and to the point. It appeared when Index's life was in a dire situation, and seemingly makes her immune to pain. She cannot perform magic at this point, and it seems that it's only purpose is to take over Index's body, when she herself cannot do it, like an Automatic Secretary.

Defense Mode
According to Index, she is incapable of magic, however, when under John's Pen's defense Mode, she is capable of accessing the grimoires in her mind. It is unknown whether or not she was capable of performing magic before losing her memories.

After Touma negated the Collar symbol put inside her mouth that was meant to kill her, the defense mode activated. Her voice retains the machine like characteristic, and her methods in eliminating enemies is machine-like. While in John's Pen Mode, she was capable of using several very powerful spells:
 * 1) St. George's Sanctuary (聖</rb> (</rp>セント</rt>) </rp> ジョージの聖域), a high class defensive spell which distorts space-time.
 * 2) Dragon's Breath (竜王の殺息</rb> (</rp>ドラゴン・ブレス</rt>) </rp>), a high class offensive spell that has the same amount of power as the legendary dragon of Saint George. This spell casts a beam of light at the target, destroying everything in it's path. It has been shown to have very long range, such as when it destroyed Academy City's satellite that housed the supercomputer, 'Tree Diagram', in outer space. The first level of this spell is enough to surpass the cancelling speed of Kamijou Touma's Imagine Breaker and the second level is enough to blow away Innocentius with ease. The after-effect of this spell is the Feather of Light.
 * 3) Eli Eli Lema Sabachthani (<rb>神よ、何故私を見捨てたのですか </rb><rp> (</rp><rt>エリ・エリ・レマ・サバクタニ</rt><rp>) </rp>) - Is a powerful anti-Christian spell which throws a powerful bloody-red beam of light.
 * 4) Scarlet Stone of Pexjarva (ペクスヂャルヴァの深紅石) - This spell causes the bones in the target's feet all the way up to the knees to feel a deep pain started to swell up. This feels like the joints between the bones being forcibly stretched apart. This invisible attack seems to be coming up from the floor and seeps into target's body from there.
 * 5) Sulfur Rain will Scorch the Earth (硫黄の雨は大地を焼く) - An area spell attack that makes around 50 arrows appear from above. These arrows strike down like guillotines, piercing and burning through the target. Just one arrow alone is enough to turn stone into dust.
 * 6) During Index's stay in St. George's Cathedral while she was being restrained by Stiyl Magnus, she grows crimson wings, which are said to be angelic wings. With them she could dissipate Innocentius and blow his user away by just flapping them.
 * 7) Index has also displayed the ability to summon legendary weapons and artifacts creating multiple copies of the same and use them to attack, all of them 'being able to suffocate the enemy just by floating in the air', some of the weapons mentioned are:
 * 8) The Sword of the Harvest God (豊穣神フレイの剣) or Sword of Victory, the magic sword of the god Freyr from the Norse Mythology, which the legends said that if someone wise possessed it, it would fight on its own and bring about victory for its owner.

Information transfer
Index is able to use the knowledge in her mind to make a Gungnir lance. In order to recreate the phenomenon, a magician of great power, skill, and mental discipline is needed to focus its power. By transferring the necessary information to Leivinia needed to draw out the design of the phenomenon from. By singing at ultrasonic frequencies necessary to keep the weapon formed, this continually exposes Leivinia to the knowledge of 103,000 grimoires through the singing putting her constantly in danger of succumbing to them poisoning her mind. Interrupting Index's continuous singing however would immediately result in the destruction of the lance. If it successfully imitated the phenomenon of throwing lance, it would likely destroy the world.

Indeed, Index doesn't need to sing to transfer a thought into someone's head. She can use a high-speed incantation, likely Notarikon, by merely moving her lips.

Other abilities
In Shinyaku Toaru Majutsu no Index SS, Index is able to read the contents of the Book of the Dead, and accurately mimic the voice of the person for whom the Book of the Dead is written for. It allows her communicate its contents with tone and feeling that perfectly matches that of the mimicked person. However, due to the unique property of the Book of the Dead, a grimoire that is different for each person a book is written for, it is likely an intrinsic part of the book and not one of Index's abilities.

Kamijou Touma
At the beginning of the series Touma saved Index from the fate of having her memories erased every year and she has been living with him ever since. She is in love with him but it is unknown if he feels the same towards her. She gets mad at him for going off to fight magicians without her and constantly turning up with new girls, and usually expresses her anger by trying to bite him. Index is still the only girl to have confessed her love to Touma, however, Touma avoided answering by changing the subject of the conversation since he had lost his memories, he had no idea about what kind of relationship he used to have with Index. Moreover, Index is also the first and one of the only girls known to have kissed Touma, the other being Shokuhou Misaki. This happened when she tried to bite him during the Daihasei Festival Arc, which caused her much embarrassment. In the Miracle of Endymion movie, Index mistook Arisa's question and describes her relationship with Touma to Arisa as one where Touma just feeds her.

Tsuchimikado Maika
Maika is Index's friend and the person she usually spends time with when Touma is away at school.

Kazakiri Hyouka
Kazakiri is a very special friend of Index's. They met during the Kazakiri Hyouka Arc and clicked right away. Even after learning that Kazakiri isn't human, Index didn't look at her any differently and they stayed friends.

Misaka Mikoto
Index considers Misaka as a rival in love for Touma. After their first meeting, both fought over who would stay with Touma. Both knew that Touma usually ends up in situations where he usually saves a girl's life and were angered at him when they found he saved the other girl's life. She also considers Mikoto to be lacking manners compared to Mikoto's clone, Sister 10032. Also, Misaka is embarassed to note that Index knows more about Japanese culture than she does, despite being a foreigner.

Kanzaki Kaori
Kanzaki and Index were close friends before Index had her memories erased. After Index had her memories erased Kanzaki tried to make more memories with her again, but after a while she gave up on this and allowed Index to think that they were enemies. Even though Index no longer remembers her, she is still very important to Kanzaki.

Stiyl Magnus
According to Kanzaki, Stiyl and Index were close friends before Index had her memories erased, but after witnessing her memory erasure each year, he and Kanzaki gave up on making more memories with Index and allowed Index to view them as enemies. As a result, despite the problem’s resolution, Index is still wary of Stiyl. The latter's antagonistic manners toward Kamijou Touma only serves to reinforce this fact. On one occasion, Index refers to him as a "despicable man” for his tendency to involve Touma in the Magic side’s affairs.

Meigo Arisa
Meigo chronologically first appears prior to the "Miracle of Endymion." There are many hard to believe stories about her, this is one of them.<sup class="reference" id="cite_ref-Amazon_1-0">[2] She apparently meets Index beforehand, and they are apparently friendly enough with each other to have a nice dinner out at a certain family restaurant.

References in other media

 * In Episode 5 of the Anime Boku Wa Tomodachi Ga Sukunai, a character named Maria (Who has the same seiyuu(voice actor) as Index and is a sister) wears an outfit strikingly similar to Index's.
 * Episode 13 of Mayoi Neko Overrun! featuring Umenomori Chise (who has same voice actress with Index) commenting how Takumi the main character born with misfortune and how Fumino possess right hand that negate luck using a voice similar to Index's.
 * In the fourth season of the anime Zero No Tsukaima, the female lead, Louise De La Vallière, as well as several other characters, wear an outfit that is similar to Index's. Also, Louise has a flat chest and a complex about it, is short, has very long hair, and is known to hurt the male lead, Saito, when angered by him.

Design evolution
As shown in the preliminary sketch for the first volume of Index, Kiyotaka Haimura drew Index with straight hair according to his own tastes. He later changed it after her description did not match her design, which not only includes her hair but her costume as well. As seen in the below illustrations, Index's gildings was originally designed differently, but was changed later as it looked to Incan.

A notable problem Haimura had was the body size that both Touma and Index, especially in regards to the body and head ratio. It was not until volume 2 that Index's body has been settled into its current form. In his drafts for her design for the manga, Haimura states that Index's design has become rounder and smaller as time went on, referring to his deformed artstyle.

Trivia

 * During the Angel Fall incident, Touma and Index found out that Index has her own Academy City ID, though neither remembers having applied for it. In the novel Touma thought it was possible using sophiscated equipment to obtain data like fingerprint, retina scans, voice imprint etc., though he doesn't know why anyone would do this. It is implied Aleister Crowley was the one responsible after making an arrangement with the Anglican Church to keep Index inside Academy City. Also, in episode 15 of the anime, Index's ID picture showed Index holding a green onion. It is currently unknown what the intentions of J.C. Staff was on this matter. This appears to be a reference to Vocaloid's Hatsune Miku.
 * According to the interview on Kazuma Kamachi featured in "Toaru Majutsu no Index no Subete", the author states that Index is the one whom he want to choose as his lover among all Index characters.
 * Touma has pointed out that Index is a sleep walker, and that will always tuck into his futon if she is left alone. This is the main reason of why Touma locks himself in the bathroom every night.
 * Index is still wearing her Walking Church, even though it has lost its powers.
 * Index's 'Dragon's Breath' is one of the few magical attacks shown so far that is able to surpass Touma's Imagine Breaker's cancelling speed.
 * Index is still the only girl to have confessed to Touma, however, Touma avoided answering by changing the theme of the conversation because since he had lost his memories, he had no idea about what kind of relationship he used to have with Index.
 * In Episode 5 of the Anime "Boku Wa Tomodachi Ga Sukunai", a character named Maria (who has the same seiyuu (voice actor) as Index and is a sister) wears an outfit strikingly similar to Index's.

Quotes

 * (To Touma, from Index Volume 1): "I'm hungry."
 * (To Touma referring to John's Pen Mode, ibid): "It feels like I’m gradually turning into a cold machine. It scares me."
 * (To Touma after losing his memories, ibid):"Touma, you don’t remember? Index… loved you."
 * (To Touma, from Index Volume 2): "Touma, this clothing is a materialization of God’s protection. I never even thought about how hard it is to wear, how hot it is, how it’s troublesome or how there should be a summer or winter version."
 * (To Touma, from Index Volume 3): "And Touma, once again, once again, once again, you kept the problem all to yourself. If you don’t discuss these things with me, I’m gonna have to give you a serious lecture."
 * (To Touma after what had happened in Angel Fall, from Index Volume 4): "No need to find excuses! You Oedipus complex boy! Always staring at your own mother, why is that attitude so different from me!!"
 * (While watching Magical Powered Kanamin, from Index Volume 5): "I see, so this Magical Powered Kanamin normally dresses like a student. No wonder even the Albigensian Crusaders of the Roman Catholic Church couldn't even get a trace of her. But what's that staff that gives out rainbow light...ah! It must be a wand that's the 5th cursed tool 'Lotus Wand' that includes the 5 elements and remade with modern materials! Ohh, as expected of Japan! Such impressive Japanese magic."
 * (After failing to activate a vending machine, from Index Volume 6): "Uu…uuuuuuuu…I became as unfortunate as Touma..."
 * (To Touma as she explains Idol Theory, from Index Volume 7): "It’s not like that, Touma. Listen to me: the condition for being an idol is being a duplicate; as long as there’s even a slight difference in the levels of magic used between the idol and the original, the idol will lose its purpose. So, the Idol Theory can’t be used to solve everything. Once the original image is changed, the theory cannot be used."
 * (To Mikoto, from Index Volume 13): "All prayers are heard."
 * (Heard by Stiyl while she is John Pen's Mode, from Index Volume 21): "Chapter 20, Verse 9. Detected a distorted Christian motif. Beginning construction of the most effective spell in response to the aforementioned spell. Preparations for the activation of the spell named Eli Eli Lema Sabachthani are complete. Activating it immediately."
 * (To a drunk Touma while girls cling to him, from NT Index Volume 2): "I was just about to say that you were being way too much like your normal self, Touma, but there’s someone I clearly don’t know mixed in!!"
 * (To Touma after he decided to go with Leivinia to Hawaii, from NT Index Volume 2):"I was really worried. I was really anxious. Touma, you don’t have a trump card that will ensure your victory. There is no rule saying that you will come back. If you continue these battles where you don’t know if you will win, the odds of you coming back will be lower. Are you still going to go despite that?"
 * (To Touma as Fräulein Kreutune clings to him, from NT Index Volume 6): "Touma! Who exactly is that girl clinging to your back!?"
 * (To Touma after the events of the Ichihanaransai, from NT Index Volume 6):"Well, at least I know you haven’t changed, Touma. ...And I suppose there is something I should say. Welcome home."
 * (To Maika after Touma didn't come home for a day, from NT Index Volume 7):"Touma really is stupid!! There was nothing but bread, cereal, biscuits, canned food, ham, bacon, bananas, and apples in the room! Does he not know that people can starve to death!?”
 * (To Touma who is amazed with her skill when it comes to food, from NT Index Volume 8):"There may be a twenty or thirty year difference, but food doesn’t change! A fried egg was perfected as a fried egg a hundred years ago!! So there’s no problem!! As long as there’s food, I’ll eat it!!"