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 and is not poisoned by the effects of reading grimoires. As such, she holds within herself 103,000 magical grimoires at the beginning of the series.

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.

Shinyaku Toaru Majutsu no Index
Due to the story shifting focus from magicians chasing her down for her grimoires (though this is apparently still something that occurs occasionally) Index takes more of a backseat role for the GREMLIN Arc which opened Shinyaku Toaru Majutsu no Index only reaching the role she had in Old Testament in the closing of the Arc. Though she takes her role as a main heroine again in the second overarching arc; the Fall of Academy City Arc, aiding Touma in battles and serving as someone he tries his hardest to protect alongside the Magic God Othinus.

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 the 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) ) 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!!"