Index Arc

The Index Arc is the first major story arc introduced in the Toaru Majutsu no Index series. The arc introduces Kamijou Touma, a young man with the mysterious power of the Imagine Breaker, living in the scientifically advanced Academy City – home of the espers.

The arc focuses on Touma meeting a mysterious nun by the name of Index which pulls him into the mysterious world of magic that coexists with science, and his struggles with the magicians who wishes to take Index. This arc occurs near the end of the Level Upper Arc in the Toaru Kagaku no Railgun sidestory.

Index Librorum Prohibitorum of Necessarius

 * Main article: Index

Index, a member of the Church of Necessary Evil is a girl who is capable of perfectly memorizing anything, and along with her ability to resist the corrupting powers of grimoires was used, or rather, allowed herself to be used as the container of 103,000 volumes of magical texts that were banned by Christendom, by the Anglican Church whose purpose was to neutralize all magic using the books. However, with such power in Index's disposal, the church was wary of her betraying the church and using the grimoires against them. Because of this, the church implanted a magical symbol inside of her mouth, as a shackle for her to restrict her use of the grimoires. The magic instilled in the symbol would kill her if her memories were not erased every year.

The Archbishop of Necessarius – Laura Stuart – lied to her subordinates of the true state of Index, which includes Stiyl Magnus and Kanzaki Kaori who were friends of Index. This forced both Stiyl and Kaori to look like enemies to Index from a Magic Cabal, as so she would not form memories with them as so to not hurt her feelings when they eventually have to erase her memories. This continued on for quite some time, until Index somehow managed to end up in Japan, and easily make her way into Academy City.

July 19
Kamijou Touma - a level 0 student in Academy City is being chased around by thugs around the city, after provoking them as so he can save them from Misaka Mikoto, a Level 5 esper. However, much to her disappointment, his plan fails as Mikoto has somehow caught up to them and has knocked the thugs out.

Finally wanting to settle their score, Mikoto tests Touma's mettle, despite his protests of being a lowly Level 0, and demonstrates her special attack to Touma – the Railgun. She later attacks him with an electrical attack, however, he is unharmed as he is able to use his ability – Imagine Breaker. Surprised that a Level 0 like him can stop an attack from a Level 5 like her without injury, she continues to attack him using a powerful electric attack that renders 80% of the city without electricity. Touma, however, was able to escape, and returns to his dorm.

At the same time, Index somehow slips through Academy City security to escape the magicians that are chasing her (Stiyl and Kaori). Moving from rooftop-to-rooftop she later slips and lands on the balcony of Kamijou Touma.

Meeting with Index
Kamiijou Touma wakes up the morning after, in a heat haze after the events of last night with Misaka Mikoto temporarily crippled Academy City's power. After lamenting his misfortune, Touma tries to air out his futon in his balcony. Here, much to his surprise, he meets Index hanging on his balcony rails. She later wakes up and begs him to feed her, he complies and offers her the now-spoiled food (due to the power outage) from his refrigerator, which she accepts readily.

Touma later allows Index into his abode and offers her a small snack as well. Here, she tells him her name is Index, of the Index Librorum Prohibitorum and a member of the Anglican Church. Touma however is completely skeptical about Index, but at least humors her a bit more. Index later states that she was being chased by magicians, because she holds the 103,000 books or grimoires prohibited by Christiandom. Of couse, Touma is completely disbelieving and confused by this, and explains to Index that supernatural powers such as esper abilities wrought by science, and his power, the Imagine Breaker the power that is inherent is right hand, may exist – a power that Touma claims that his power to deny God's miracles – but certainly not magic. Index belittles Touma because of this, to which Touma demands Index show proof that magic, so that he can destroy it with his right hand, and hence prove that his power is real as well. Not having any mana to use magic, Index suggests that Touma prove his power by destroying her magic robe – the Walking Church. Seeing this as a challenge, Touma obliges and destroys Index's Walking Church. This is much to her irritation, causing Index to bite Touma in response, before repairing the now powerless robe afterwards. After fixing her robe (which has lost its magical powers of defense) Index opts to leave, not wanting Touma to get involved, and with Touma having to go to his remedial lessons, it seems he has to leave Index as well. However, Touma is concerned for Index's safety and allows her to stay in his apartment, now believing that magic actually exists. However, Index insists on leaving.

Before leaving however, Index gives an explanation regarding his Imagine Breaker, that not only does it negate powers, but it also negates God's blessings – his luck and destiny – as well. Which means as long as Touma has his right hand, misfortune will always be before him. Touma continues to persuade Index into saying in his room for her own safety, however, Index states that the magicians can still track her. Hearing all this, Touma asks Index if she thinks he would simply let her go after hearing her story. To which Index replies by asking: "Will you accompany me to the depths of hell?". With that, Index leaves smiling, deciding to go a Anglican Church for sanctuary.

However, Index has apparently left her headdress back in Touma's room.

Prelude to battle
Touma is later forced to stay in his remedial class with Tsukuyomi Komoe for much longer as punishment, because of this, Touma arrives home much later in the evening.

While going home, Touma once again encounters Misaka Mikoto, who challenges him once again to do battle, which Touma promptly ignores. Out of anger Mikoto discharges electricity and cripples several electronic devices. They later try to run away from the security bots alerted by Mikoto's callous use of her powers.

Kamijou Touma vs. Stiyl Magnus
Touma later returns to his dormitory after dealing with Mikoto. He, however, discovers Index lying in her own pool of blood. Immediately after his discovery, a magician named Stiyl Magnus comes along and explains to him that Index may have returned to Touma's dormitory to retrieve her missing headdress. Touma then realizes that the headdress may have still exuded magical energy and that Index returned to retrieve it since it would put Touma in danger, which makes Touma feel guilty. Looking at an enraged Touma, Stiyl states that he was not the one who hurt Index but Kaori, although she did not intend to injure Index at all since she was wearing her Walking Church, which was somehow destroyed.

Touma asks how the magicians act like they were just and still be able to run around and attack a little girl like Index. After allowing Touma to finish his talking Stiyl states that he needs to reclaim Index, the holder of the 103,000 grimoires banned by Christendom. Stiyl explains to Touma that the grimoires are inside Index's head making her like a magic librabry, as she has photographic memory and is able to perfectly memorize anything. However, she has been rendered harmless because she can't use magic especially that from the grimoires. Stiyl says that it his job to protect her because she is defenseless against magicians coming after her. Angered by his words Touma attacks Stiyl, however, he replies by introducing his name and magic name to him – Fortis931. Immediately afterwards Stiyl demonstrates the power of magic to Touma, and then uses fire to attack him.

Presuming that his attack destroyed Touma, Stiyl returns to try and collect Index. However, he soon realizes that Touma survived, which Touma comments that his right hand actually works on magic. Flabbergasted by the strange phenomenon of Touma somehow appearing from the flames unscathed, Stiyl tried to attack Touma again but the result remained the same, as Touma simply slaps away his magic. Seeing that Touma was the one who destroyed Index's Walking Church, Stiyl begins his incantation and summons Innocentius.

Innocentius attacks Touma and predictably it gets dispelled, however, much to Touma's surprise, Innocentius reforms anew and initiates another attack on Touma. Here, Touma realizes that Innocentius is indeed negated by his right hand but it reforms instantaneously as well. However, Index suddenly regains consciousness, and explains to Touma on how runes have allowed Innocentius to reform even after Touma negates it. Touma however, realizes that it isn't Index the little girl he met before, but that of her John's Pen Mode which activated. Regardless, Touma is forced to escape as Stiyl attacks while Touma is preoccupied with Innocentius.

Touma later sees that Stiyl has stuck several runic markings on paper all over a section of the apartment building, however, his discovery is cut short as Innocentius pursues him once again. While escaping, Touma falls from a considerable height, though he manages to land without much harm, and learns that Innocentius' movements are limited by the runes Stiyl placed. Kamijou uses the time to try and find some help, however, he realizes that he is simply making excuses to himself, and that he is actually hesitant to save Index and get dragged into the 'hell' she mentioned previously. Realizing this, Touma decides he does not want to follow her into hell, but to drag her out of it. Now determined to see through his path until the end, Touma formulates a plan to defeat Stiyl and his Innocentius.

Touma purposely sets-off the fire alarm to activate the dormitory's sprinkler system. He shows himself before an amused Stiyl who states that Innocentius cannot be killed with a mere 20th century fire prevention system, and calls out to Innocentius. Touma states that he did not turn on the sprinklers on to douse Innocentius but to make useless the paper of the runes Stiyl pasted all over the building. Stiyl is rather amused by this as well and says that the paper he used will not be torn by mere water. Touma however, corrects Stiyl regarding this and states he wasn't targetting the paper directly, but the ink that Stiyl used to write his runes down. After hearing this, Stiyl begins to cower but is soon relieved as Innocentius returns to attack Touma. However, Innocentius is immediately dispelled by Touma and this time does not reform.

With Innocentius destroyed, Touma begins his charge towards Stiyl to defeat him. Meanwhile, Stiyl tries to conjure up another spell to counter Touma. Stiyl however is too late, as Touma knocks him out with a single punch to the face.

Healing of wounds
Touma escapes with Index whilst the authorities deal with the fire that has emerged from Touma's apartment building. At the same time, Touma finally destroys the magic in Index's headdress preventing them from being tracked by magicians. However, Index is still critically injured and he cannot use the city's medical coveniences because Index is an outsider. Touma, in desperation asks Index if there are any spells in her grimoires that can heal wounds. However, Index points out the flaw in Touma's plan, stating that espers such as him, cannot use magic.

Hearing this, Touma goes to the only person he trusts that is not an esper, Tsukuyomi Komoe. Here, Komoe is forced to accomadate the queer arrival of Touma and Index. Index's John's Pen Mode awakens once again to prepare for the magical healing ritual, and asks Komoe to help her. Index however, states that Touma should leave as his right hand will interfere with the ritual location and cause the ritual to fail. With this Touma, reluctantly complies with Index's orders and leaves the premises, leaving Index's life in the hands of Komoe.

8:30 PM. As soon as Touma leaves, John's Pen Mode Index begins to ask Komoe questions and instructs her on what to do in order to make the healing ritual successful, much to her reluctance and disbelief. Index teaches Komoe a rather complex spell that requires a model to be an exact replica of Komoe's room, as well as to summon an image of angel. Although Komoe fumbles a bit during their performance, they're successful in healing Index of her cut without harm on Komoe and with this, Index announces that she will leave John's Pen Mode and will now enter sleep mode. A tired yet lucid Index says to Komoe on how she is relieved that she is alive, as Touma would not need to shoulder the burden of her death, before falling asleep.

July 21 to 23
The day after, Touma somehow manages to weasel his way out of explaining his relationship with Index and the unusual situation they were in to Komoe. However, she willingly lets the matter slide herself and does not report Index to the higher-ups, despite her responsibility as a teacher and an adult in the city. After Komoe goes out for a while, Touma takes care of a still-recovering Index. Here, they discuss the secret world of Index, and basic information about the magical organization that Index is in, the Church of Necessary Evil – Necessarius. They continue on about how the 103,000 grimoires came to be inside Index's mind, which is for the sake of analyzing magic as so to defeat the magic that Necessarius is against. Index continues by explaining the dangers that grimoires can wrought, and with Index being a convenient storage for all the grimoires for the world, notes the danger on how a single person could acquire them and distort the world. Touma becomes enraged after hearing this, to which Index apologizes, as she didn't want to be hated by him, however, Touma states that he would not look down on her just because she held the 103,000 grimoires and states that she should have faith in him.

All the while, Stiyl Magnus and his partner Kanzaki Kaori have found Komoe's apartment and are observing Index vigilantly. Here, they discovered that Touma is neither a magician nor an esper, and conclude that information regarding Touma has been intentionally hidden. Stiyl later notes on how Index is living happily and laments on how they have to tear it apart again, with Kaori referencing how Stiyl was in the same position as Touma is now, in the past.

Stiyl Magnus later takes 3 days (exactly sixty hours) to cover a two kilometer radius with 164,000 rune cards to set up a trap for Touma.

July 24
Stiyl and Kaori initiate a trap against Touma, during the night of July the 24th.

Meanwhile, Touma and Index decide to go to a bathhouse together. While going there, Index (who now knows and calls Touma by name) divulges to him on how she believes she arrived in Japan a year ago, and that she has no memories before that, though she retained knowledge regarding magic and the 103,000 grimoires. Hearing this though, shocks and irritates Touma. Seeing Touma angry, makes Index misunderstand and they get into an argument, with Index running away.

Kamijou Touma vs. Kanzaki Kaori
While on his own, Touma comes upon an area with an oppressive atmosphere, and discovers that he is in a trap – a barrier spell powered by a rune that isolates chosen individuals within a vicinity, by diverting other people's attention elsewhere. Here, a magician named Kanzaki Kaori appears before him. She states she would rather just take Index than fight and potentially kill him, and demonstrates her power to a helpless Touma.

Foolishly, Touma does not yield to her request which forces Kaori to attack him – Nanasen – an attack that uses thin, sharp steel wires that is able to kill someone seven times in an instant. Terribly outclassed, Touma tries to find a way to go around Kaori's attack and discovers that it is not actually magic, but an attack that only seems like an illusion, making his Imagine Breaker utterly useless. With this however, Touma is once again hurt by another attack by Kaori.

Still unyielding with Kaori's request, Touma desperately tries to attack Kaori, however, is constantly struck down by Kaori's attacks. After dealing another blow to Touma, Kaori states that Touma shouldn't have a reason to continue fighting this much for Index, seeing that he is still alive. However, Touma asks Kaori why she hasn't killed him yet. He targets the fact that they are human, and asks them why they're allowing themselves to do something as intolerable as trying to catch Index, who has already lost her memories (due to trauma) because of them, with a power that she could use as a way to protect her.

Touma asks Kaori why they are taking this course of action, to which she replies that she had no choice as Index would die, and states that Index is a precious friend.

Touma discovers that Kanzaki Kaori is a member of Necessarius; a fact that surprises Touma as he never thought that Index's own faction would attack her. During their confrontation, Touma learns that both Stiyl and Kaori are members of Necessarius, and are out to retrieve Index so as to erase her memories again. Kaori explains that Index requires that her memories be erased every year, so she can live because she can perectly memorize anything, preventing her mind from getting rid of the unnecessary memories. She also explains why they presented themselves as enemies to Index; so she would not be hurt again by the knowledge that they are friends when the time comes for her memories to be erased,.

During the entire battle, Touma is unable land a single blow on Kaori, as she is not using magic in her attacks that are injuring him severely. Despite this he perseveres, and delivers a rebuttal towards her actions. He states, that they are just being selfish towards Index, as they did not take into account on what Index would feel if her friends carry on the burden of trying to erase her memories as so that she can live. He goes on to state that regardless of Index losing her memories and forgetting the friendship between them, there is no stopping them in trying to become friends with her again regardless of what they had to do. Touma manages to strike Kaori in the face with a pitifully weak blow, hurting himself more than her, yet Kaori reacts as if she has taken a large blow.

He collapses due to his injuries, and is later carried back by Komoe to her apartment.

July 27 to 28
Touma wakes up three days later, with a worried Index beside him. Here, he is surprised that he is somehow still alive, though it worries him that his business with magicians is not over. He however, is unable to do anything because of his current condition. Because of this condition however, Index begins taking care of Touma, though poorly.

Touma however, realizes that July 27 was the day that the magicians were planning on erasing her memories, and it became obvious that Index's health was deteriorating as well. Predictably, the magicians came to take Index away, and Touma is unable to defend her from them. However, Index steps into the front and tries to protect the powerless Touma on her own, and begs them that she'll do whatever they want in exchange for them not to hurt Touma anymore. Although reluctant, Stiyl and Kaori concede and leave them for a while before the appointed time.

Appointed time
Index is later overcome by sleep and is resting in Komoe's room, Touma however is awake and anxious of the time limit the magicians setup with Index. He is later reminded by Kaori that they are still going through with the plan to erase Index's memories and that she has called beforehand to tell Touma to say farewell to her.It was basically an order for Touma to give up. Touma demands to know why the magicians can't deal with their dilemma with magic, to which Touma discovers there is no magic that can be done with what Index is experiencing, as the Church who is afraid of Index rebelling against them has but up measures against her such as a Collar that shackles her so that a maintenance only the Church can perform must be carried out once a year by erasing her memories.

Irritated with the incompetence and still unyielding, Touma in desperation, asks them if they can use the facilities of the Science side - Academy City, but is denied by them as there is no time, and that they would not allow science to tamper with her. Hearing this, Touma decides to give up on attempting Kaori to change her side in the manner, and brazenly declared that he will save Index on his own. Kaori later states that they'll live him be until midnight when they will begin preparations to erase Index's memories.

With that, Touma is forced to find a way a solution to help Index on his own, however, he is too late with Kaori and Stiyl arriving in Komoe's door, prepared to do their jobs.

Collar
With time of the essence, they prepare the ritual in erasing Index's memories again. However, Touma tries to plead to them to give him another chance to use the Science side to save Index. However, Touma's pleading is condemned by Stiyl for recommending them to do a gamble that he though that would help Index.Touma is then challenged by Stiyl to destroy the magic on his cross that would help in brainwashing Index, if he is confident enough with keeping Index alive; although hesitant, Touma decided not to do it, and with helplessness to help Index he falls into despair.

Seeing Touma's despair, Kaori however decided to give Touma 10 minutes alone with Index, much to Stiyl's protests, who is reminded by Kaori on how they were in the same position as Touma now. With this, Touma is left alone with Index again.

With Touma and Index alone, Index temporarily awakens to find a incredibly distraught Touma. She notices the magic formation that they were preparing and quickly tells Touma to depart, however, he calms her down and tells her that it will be all over now as he will definitely save her this time. Buying his lie, Index becomes relieved and falls asleep once again. However, Touma remains vexed that he cannot do anything for Index and even lying to her.

While feeling helpless, Touma later becomes suspicious of the explanation and mathematical data of the church on why Index needed her memories erased. Realizing this, he tries to call Komoe again and finally connects, here he calls Komoe and human's memory. She reveals that even if someone was capable of perfectly memorizing anything, it does not imply that the brain would not be able to handle it, as it has several parts that govern certain functions, one of which is memory, she continues on that the human brain can store hundreds of years of memory without problems. Touma, knowing that the church lied tries to find some magical apparatus that is making Index sick, fortifying to himself that he is the hero that will save Index.

After much pondering and searching of using his right hand on Index's body, Touma opts to use his right hand inside Index wherein discovers that there is a magical symbol stuck within the roof of her mouth and decides to dispel it. It works, however, it injures Touma's hand and activates Index's John's Pen's defense mode, and makes Touma the target.

Kamijou Touma vs. John's Pen Mode Index
With the destruction of the Collar that shackled Index to the Church, John's Pen's defense mode activate and makes Touma its target. Unable to find the Imagine Breaker in her inside the 103,000 grimoires, John's Pen Mode Index uses St. George's Sanctuary to distort the fabric of spacetime within Komoe's room as a defensive measure against him. Index attacks Touma with a powerful laser-like beam attack called Dragon's Breath, forcing Touma to use his right hand to counter it, however, it could not be negated immediately, as it was similar to Innocentius, continuously regenerating. A perfect a attack against his right hand, which completely preoccupies Touma and began to wear him down. Stiyl and Kaori, discovers the ruckus as well, whereupon they are shocked to find that Index could display let alone perform such a powerful magic. Touma tells the unbelieving magicians while fending off Dragon's Breath that their church was lying to them all the time about Index. All the while, Index switches to another spell to destroy Touma.

Although, hesitatant, Stiyl calls out his magic name to aid Touma against the onslaught of Index's attack. Stiyl states that he needs does not need any ambiguous possibilities as long as he could save her life, then erasing her memories would be a better choice. Touma tells that choosing the still awful alternative to Index having her memories erased is pathetic, Touma demands to know from the magicians if they want to save Index. He continues by saying that the moment where they need no longer to have her memories erased to save her life is now present before them. An ending were everyone is happy, Touma gives them a challenge to save Index. While telling them this, Touma's right hand began to rip apart due to the pressure of Index's attacks, but sill tries to resist.

Before Touma's hand becomes overwhelmed by Index's attack, Kaori calls out her magic name and saves him by using her Nanasen manages to make Index lose her balance, making her fire Dragon's Breath towards the sky, destroying Komoe's roof and destroying an Academy City satellite orbiting space.

This however, creates Feathers of Light fall from above which, Kaori warns them not to touch it or they'll be doomed. Immediately afterwards, Index recovers to start her attack again, which catches Touma completely offguard. However, he is saved by Stiyl who has finally summoned Innocentius to take on the attack by Index's beam. With this, Stiyl gives Touma an opening to strike Index, trusting Touma to save Index. Seeing, Innocentius however, John's Pen Mode Index tries to change its target to Touma again as he is of the highest priority. However, Innocentius continues to protect Touma and absorbs its blows.

Touma charges towards Index, whilst St. George's Sanctuary is still in place, forcing him to take some time to get to Index. While Touma charges towards Index, she once again changes her strategy and successfully reversed-engineered Innocentius and manages to strike a killing blow at it. However, Touma is already within range of Index, and states that if the world is a system created by God and move according to his will, then he'll destroy that illusion first. With that Touma reaches Index, and destroys the illusion placed upon Komoe's room, returning Index back to normal. However, as consequence a Feather of Light touches Touma's head and falls with the girl he has saved and still continuing to protect her body from the feathers. Kamijou Touma symbolically died on that night

Aftermath
Touma is sent by Kaori and Stiyl to a certain hospital where the Frog-faced doctor works in, where he successfully revives Touma but is unable to restore his memories.

Index is present in the facility as well, where he says that Index perfectly healthy. Here, Heaven Canceller tells her the truth of Touma's condition. Index also reads Stiyl's poorly constructed letter to Touma. The letter states that they were technically ordered to take back Index since the Collar has been removed, however, they are forced to acquiesce to keep the status quo with Index living with Touma, as the truth has been revealed regarding their lying to Stiyl and Kaori, though Stiyl states that they probably just want to monitor her. Stiyl notes that they'll retrieve once they obtain the necessary materials. The letter later harmlessly explodes, a final rude gesture by Stiyl to Touma, though Index gets instead

Before visiting Touma's ward, Heaven Canceller warns Index that Touma will not recognize her. Saying that Touma did not have memory loss, but had memory destruction, which in layman terms mean that his memory can never be recovered ever. Even then she steels herself and enter Touma's room. Predictably, Index realizes that Touma has no recollection of various events that occured, as well as his name, in the end, Index is in the verge of crying where she outright confesses to Touma that she loves him.

However, before she could cry in earnest, Touma laughs and tells her that he was joking and that his memories have been restored after using his right hand on his head. This made Index angry, punishing him by biting him several times and leaves. However, the Heaven Canceller, after seeing their shenanigans, asks him if he judged correctly on not telling Index the truth. It is revealed that Touma actually did lose his memories and that the only thing that he seem to deem as fact, is what the doctor told Touma regarding what the magicians told him on what happened to Touma.

Touma tells him that he lied because he did not want Index to cry. He further states that even if his memories are lost from his mind, they will always remain in his heart.

Trivia

 * In the Toaru Kagaku no Railgun manga, the blackout caused by Mikoto due to fighting Touma on a bridge after failing to get information on the Level Upper is the same event that appears in the beginning of Toaru Majutsu no Index. This event was completely changed in the anime adaptation as Mikoto caused the blackout while fighting Elder Sister, the anime still indicates that Mikoto fought Touma on a bridge which implies that in the anime's timeline, there were two blackouts that were caused by Mikoto.
 * Komoe later references the incident where the roof of her house got destroyed, in episode 17 of the Toaru Kagaku no Railgun anime to Tessou Tsuzuri.
 * Heaven Canceller not reporting Index for being an outsider shows his professional neutrality as a doctor, a trait which he carries throughout the entire series until the end of Academy City Invasion Arc, where he tells Aleister Crowley to stop his playing with his patients, though he remains neutral to the activities of the characters even after that.
 * Index is still the only girl in the series to have confessed to Touma of her feelings.
 * The anime adaptation combines the end of the arc with the beginning of the next one, more specifically the prologue of the 2nd Light Novel.