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 series and is considered the main heroine of the Magic Side. She is a member of Necessarius and has a Photographic Memory. She holds within herself 103,000 magical texts known as grimoires.

Etymology
Her name is based on the book with the same name, The List of Forbidden Books or "Index Librorum Prohibitorum" (禁書目録 or Kinsho Mokuroku 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, 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
She is often elated by things that an adult would find mundane and is slightly ignorant and curious of modern technology. She is 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. She can be easily irritated specially 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), occuring even in serious situations or in front of important persons. 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.

Touma has pointed out that she is a sleep walker, and that will always tuck into his futon if she is just left alone. This is the main reason of why Touma locks himself in the bathroom every night.

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. 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 her 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 care 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, though in certain storyline she takes more of a back-seat role, especially during Science-side storylines as seen during the Sisters Arc in which Misaka Mikoto could be considered the lead female.

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 Kaori Kanzaki, 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. Some time afterwards she discovers that Touma has been beaten to unconsciousness (by Kaori Kanzaki) 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 efforts 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 Piasu 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 the 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.

The Fake Date and the Kamijou Faction
While Touma is on his fake date with Mikoto, unbeknown-st 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.

Accelerator and 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 them changing 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 Liver AL ver 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.

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.

Acqua of the Back Arc
Index is initially distressed that Touma has brought home yet another girl, however Itsuwa could quickly gain Index heart using her excellent culinary skills. Touma, however; inspired by Itsuwa's usefulness when it comes to house work, Touma removes her 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 hotsprings, where she meets Misaka Mikoto and has a little quick exchange until Mikoto feints 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 knew who was Touma actually fighting until the very end, a fact that she used to scold Touma; along with his night time escapade from the hospital.

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

British Royal Family Arc
She is kidnapped and forced to go to England along with Touma.

At the end of the arc, Fiamma of the Right takes the Queen's controller over Index. Afterwards, Touma leaves for Russia, so he could free Index from Fiamma's control.

World War III
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 couse 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.

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 found out and proceeds to bite him.

Leivinia ended a conference call with the allied nations and said that the preparations are complete. Index thought that she ordered a pizza to which Leivinia replied that whe would rather order sushi or soba since she is in Japan. As they were eating their breakfast, Index finished her food quickly and demanded for more and Touma initially refused but agreed later on. Leivinia explained the reason they came to Japan and that they need Touma's help, to which Touma refuses at first but then agreed after the threats and explanation of Leivinia. She then told them the location of GREMLIN's headquarters..

She was then asked by a sleepy Lessar if it is okay for her to let Touma go, to which Index replied that complaining can't stop Touma and she had an idea. They then proceeded to go to District 23 and walked on the same path where students go to school and Touma felt awkward at the looks of the people due to the fact that he is with foreign girls. Lessar then told him that they won't falter when faced with alienation in that level. They then waited for a bus to District 23, and as Touma sat on the banch near the stop, Leivinia sat on his lap and Lessar clung to his arm saying that she is still affected by jet lag. Index then became mad at the sight before her and proceeds to bite him as usual.

Index and the others are at District 23 International airport. Lessar and Leivinia then proceeded 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 insisted on going to "50% Less Skin Covered" swimsuit store to which Touma refused and instead suggested to have voting to which store to go. Touma tricked Index that "Tropical Bright Girl" sounds more delicious and thus got her vote. Touma won and they proceeded to the other swimsuit store (Tropical Bright Girl). On their way, Mikoto then asks Index if these crazy things always happen to him to which Index responded that this is just the third link of the chain. As they enter the store, Index said that she would be fine with any store as long as it has food and Touma reacted that whether she has finally reached the point wherein she will also eat swimsuits or cellphones as well. Index then exclaimed that she can smell cafe's and bread shops around. Touma was amazed at her skill when it comes to food and Index told him that food doesn't change and as long as there is food, she will eat it. Mikoto then said to Index that she must not underestimate the advances made by science and said that even a trash meat in Academy City is much better than the average in the outside world. Index then screamed at Touma to which Touma responded that he can't afford such a high class meat. They then entered the swimsuit shop and Index said she doesn't care about swimsuits since it is November and asked Touma when will they go to eat. Index, Leivinia and Mikoto then caught Lessar who was overcome by shock due to Touma defeating her sex appeal and Touma holding a swimsuit and misunderstood the situation. .

They met Kumokawa Maria at the airport and asked Touma who is this another girl yet again that she doesn't know about. After recieving word that Sargasso has already been located, there was a low rumbling in the earth. Touma ran off with Index and Mikoto following him. After letting Mikoto go with him, Index demanded to go too to which he agreed. Index and the others proceeded to ride an electronic cart to the plane. As the plane left Academy City, it was sliced in half by a giant dragon. Index and the others were mercilessly thrown out into empty air.

GREMLIN invasion of Tokyo
As Index and Mikoto are falling from the sky, Mikoto stopped using her parachute and caught Index who is chaotically rotating as she fell. Mikoto then controlled magnetism and landed vertically on the wall of a giant train station building while holding Index. Mikoto was dumbfounded that the place was so packed with people to the point that she can't see the sidewalk. Index then told her that it was GREMLIN's doing. Suddenly, a giant dragon flew over their heads but did not attacked them. Mikoto then tried to use her cellphone but it was of no avail since the lines were apparently overloaded. Mikoto then started to move from building to building using her magnetism and while still holding Index. They are heading for Sargasso since Mikoto thought that Touma will probably head there. While moving, Index then warned Mikoto to watch out and they landed perpendicularly on the side of a high rise building. As soon as she did, countless of sparks appeared floating down and each spark struck the glass wall and produced pillars of flame that took form. Index then explained that it is the Muspell from the Norse Mythology to which Mikoto doesn't understand.

While still holding Index, Mikoto used her magnetism to jump from wall to wall. They were being pursued by the Muspell but they tried to escape them. Mikoto then asked Index if she knew where they are right now to which Index responded that she doesn't know. They then wondered what happened to Touma then suddenly they saw an Academy City bomber and realized that Academy City has already made their move. They also saw an eagle-like creature that flew to which Index said that it was Hræsvelgr and explined it to Mikoto. Suddenly, the creature fell toward a wide open space.

Mikoto while holding Index just saved Touma just in time before he is about to fall. Index was then released by Mikoto and she proceeded to scold him to which Index said that it won't change Touma. Index then told Touma that she would be going this time and he won't be backing down no matter what he says. Touma's cellphone then fell down while some button was pressed and he heard his mother's voice saying that she is fine and they don't have to worry. After hearing that, Touma then told Index and Mikoto that the opponent he's facing now is Freyja and he asks them to lend him their power so that he would be able to save both Freyja and the mother to which the two responded that he leave it to them.

Just as Freyja commanded Nidhogg Vol. 02 to attack them, Mikoto attacked it using her ability and repeatedly fired railgun at it at point blank range. The dragon was stopped and Freyja was dumbfounded. Freyja then summoned more creatures however, Index casted spell intercept. Touma then told her to analyze the magic being used to give birth to those '"children." Touma then persuaded Freyja to let Index finish the spell and help her rather than relying on the magic god. Index then analyzed the spell while Touma takes care of the others that tries to interfere. While Touma rushed to his opponents, Index then muttered an incantation and everything went back to normal. The mother was unaware of what is happening and where she is then she fell unconscious. Index then asked Touma on what they should do now to which Touma responded that they must ensure the safety of the pregnant woman. They sneaked on a different train and arrived on a switchyard near the bay. They then saw Leivinia, Lessar and Maria on a rubber boat and met them. Mikoto also came last and scolded Touma for leaving her behind after that bold announcement, as well as the fact that he is going after a pregnant woman to which Touma dealt again due to misunderstanding. They rode the boat and left for Sargasso. On their way, they were attacked by Nidhogg and while they are preparing to counter it, Kagun defeated it. Maria then recognized that it was Kagun and decided to go with him, along with the pregnant woman. Index and the others then continued on to Sargasso wherein they were met by Mokkerkalfe, but it was killed by Thor (Ollerus in disguise). .

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 to 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, he 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 is he 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 esentially 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 gout 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 he touches her with his right hand. Othinus tells her that there should be no problem in him touching her as she is a neutral magic god, but she can't say for sure 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 by America and imprisoned. Othinus tries to explain but before she can do so, Sphynx jumps off Index and onto the bed toward Othinus, surprising her. Othinus asks for help, but Touma says he is unable to dos in his condition. As she is held in Sphynx's mouth, Othinus recalls what had transpired after she became small and after Touma finally collapsing 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 happiness 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.

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.

Toaru Majutsu no Index: Love Letter Competition

 * Main article: 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

 * Main article: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.

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 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 to 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 commerical featured by Motoharu and Aogami Piasu, 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 kuroko 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 ''[http://en.wikipedia.org/wiki/Shinryaku!_Ika_Musume Shinryaku! Ika Musume]''. 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)

 * Main article:Toaru Majutsu no Index (PSP game)

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

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 (refering 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 MMORPG 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
Her sorcery name is 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
Photographic Memory (完全記憶能力): She is capable of perfectly memorizing anything, such 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.

Abilities-related to being the Index Librorum Prohibitorum

 * Main article:List of Grimoires'

She can also have abilities that require no mana whatsoever, for they are not of magic, but simply due to the knowledge that Index 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 causes the magic to go berserk or be outright cancelled. .

Sheol Fear
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. Although 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 is seemingly immune to pain. She cannot do 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. Her self-protection system will use the "Feather of Light" to force a reset on Index's own memory should a manual reset fail to be performed.

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, like when it destroyed Academy City's satellite that housed the supercomputer, 'Tree Diagram', in outer space. It is also shown that the first level of this spell is enough to surpass the cancelling speed of Kamijou Touma's Imagine Breaker and at it's second level, is enough to blow away Innocentius with ease. The after-effect of this spell is the Feather of Light.
 * 3) Eli Eli Lama 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 his knees to feel a deep pain started to swell up. This feels like the pain from the joints between the bones being forcibly stretched apart. This invisible attack seems to be coming up from the floor and seeped into target's body from there.
 * 5) Sulfur Rain will Scorch the Earth (硫黄の雨は大地を焼く) - A area spell attack which throws about 50 arrows appearin from above which strucks down like guillotines piercing and burning through the target. Just an arrow alone is enough to turn stone into dust.
 * 6) During her stay on St. George's Cathedral while she was being restrain by Stiyl Magnus she grows crimson wings which is said to be angelic wings, with them was enough to dissipate Innocentius and blow his user away with just flapping them.
 * 7) She 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 the Harvest God Freyr (豊穣神フレイの剣) or Sword of Victory, the magic sword of the god from the Norse Mythology, which the legends said that if someone clever possessed it, it would fight on its own and bring about victory for its owner.

Other
Index is capable of singing in ultrasonic frequencies, using it to transfer information.

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 among other things, and usually expresses her anger by trying to bite him. 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. Moreover, Index is also the first and only girl known to kiss Touma (by the cheek) when she intended to bite him during the Daihasei Festival Arc. In the Miracle of Endymion movie, Index 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 start to look at her any differently, and they stayed friends.

Misaka Mikoto
Index considers Misaka as a rival in love. After their first meeting, both fought over who would stay with Touma. Both knew that Touma 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 and compares Mikoto, ironically, to her well mannered 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 more memories with Index 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 serve to reinforce this fact. On one occasion, Index refers to him as “despicable man” for his tendency to involve Touma in 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 are apparently friendly with each other to have a nice dinner out at a certain family restuarant. Realizing they have no money, they have to wash dishes to pay for it.

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 Index like voice.
 * In the fourth season of the anime Zero No Tsukaima, the female lead, Louise a la Valliere, 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 for some unknown reason Index holding a green onion. It is currently unknown what the intentions of J.C. Staff was on this matter. Probably 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.

Quotes

 * (Volume 1): "It feels like I’m gradually turning into a cold machine. It’s scares me."--- Referring to her John's Pen Mode
 * (Volume 1):“Touma, you don’t remember? Index… loved you.”---To Touma after losing his memories.
 * (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 referring to her nun's habit
 * (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 in the hospital
 * (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!!"--- To Touma after all that happened during Angel Fall
 * (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.”--- While watching Magical Powered Kanamin
 * (Volume 6): "Uu…uuuuuuuu…I became as unfortunate as Touma…"---After failing to activate a vending machine
 * (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.”---While explaining Idol Theory to Touma
 * (Volume 12): "All prayers are heard."---To Mikoto
 * (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 Lama Sabachthani are complete. Activating it immediately.”---Against Stiyl while in John's Pen Mode
 * (NT 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 a drunk Touma with girls clinging to him
 * (NT 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 once he decided to head to Hawaii along with Leivinia Birdway
 * (NT Volume 6): “Touma! Who exactly is that girl clinging to your back!?”---To Touma on a plaza.
 * (NT Volume 6):“Well, at least I know you haven’t changed, Touma. …And I suppose there is something I should say. Welcome home.”---To Touma after the events of the Ichihanaransai.
 * (NT 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 Maika after Touma didn't come home for a day
 * (NT 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!!”---To Touma who is amazed with her skill when it comes to food