The first arc of A Certain Magical Index, consisting of volume 1 of the light novels, chapters 1-10 (volumes 1-2) of the manga, and episodes 1-6 of the anime.
Academy City is an independent city located inside Japan, where advanced technology and esper powers are developed. By going through the Power Curriculum, a person has a chance of developing an esper power. Powers are ranked from Level 0 to Level 5; a Level 0 either has no powers or a relatively useless power, while a Level 5 could potentially take on the world's armies and win.One night, Touma Kamijou sees some bullies trying to sexually harass Mikoto Misaka. Touma provokes the bullies and then runs, leading them on a chase through the city. He stops to catch his breath on a bridge, but Mikoto shows up and says she took care of the bullies already. It turns out that Mikoto is The Ace of Tokiwadai Middle School, the third most powerful Level 5 with control over electromagnetism. Touma knew this and was actually trying to save the bullies' lives, and he complains that he failed. Mikoto clarifies that she's not a killer, so she just fried them with lightning to put them in severe pain. She challenges him to a fight. He refuses, saying he's just a Level 0. She refuses to believe that, citing what she's seen him do in the past. She demonstrates her Railgun attack, where she uses electromagnetism to launch an arcade coin at Mach 3. Depending on the adaptation, Touma either sidesteps the attack or catches it. Mikoto then releases enough electricity to trigger a blackout, but Touma is still unharmed. He quips that she was unlucky.
The next morning, Touma wakes up in his apartment slightly miserable. The blackout meant that his air conditioner didn't work, and the food in his refrigerator spoiled. He also stepped on his ATM card and broke it. He then finds a girl with knee-length, silvery hair wearing a nun's habit hanging from his balcony. She incessantly says she's hungry, so Touma offers her some slightly spoiled food, and to his shock, she gobbles it all up. She thanks him and introduces herself as a nun in training, Index Librorum Prohibitorum. He thinks that name is fake, but she protests and also says her magic name is Dedicatus545 - The Dedicated Lamb Protects The Knowledge Of The Strong.Touma is baffled by this, so Index explains that she is a magician on run. Due to her Photographic Memory, she has memorized 103,000 grimoires, and now several magical cabals want to capture her to use the knowledge for their own desires. She entered Academy City during the blackout seeking sanctuary, Roof Hopping until she landed on his balcony. Touma scoffs at this, saying that he knows that advanced technology and esper powers are real because they have a scientific basis and structured laws, but magic is just fiction. He asks her to prove that magic exists by performing a spell, but she says she does not have any mana and can't perform magic on her own. Normally, reading a grimoire would cause catastrophic damage to the reader, but since she doesn't have any mana, the texts she read didn't do anything to her.Index is annoyed that he won't take her word that magic is real, and asks what kind of esper power he has. He explains that ever since he was born, his right hand negates any kind of supernatural activity on contact, including esper powers and acts of God. However, since Academy City's System Scan could not detect anything from him, he was branded a Level 0, and he decided not to correct them. It is Index's turn to scoff, because of his Blasphemous Boast that he could negate acts of God. She explains that the nun's habit she's wearing is a sacred garment called The Walking Church, which is enchanted to be completely indestructible, except against something sufficiently powerful like the Dragon of St. George, and challenges him to use his right hand on it. Annoyed, Touma touches her on the shoulder. At first, nothing happens and Index mocks him, but then her clothes fall to pieces, leaving her naked. He's shocked and tries to apologize, but she angrily jumps on him and bites him several times.Index wraps herself in a blanket and tries to repair her outfit, and settles for using several safety pins to hold it together. She thanks Touma for his hospitality and food and says she must be going, for until she reaches an Anglican church, her pursuers will never stop chasing her. He says she's welcome to come back and stay as long as she likes. She asks if he would follow her all the way to Hell, hinting that he would be in danger if she stayed with him. He's disturbed by the question and she leaves. She turns back to say she now believes his claim that his right hand can cancel acts of God, and says that the reason he is so unlucky is because his right hand negates luck itself. As she's walking away, she gets surprised by Academy City's cleaning robots, calling them Agathions (Familiar spirits). Touma notices she left her hood behind, but when he turns back, she's gone.Touma goes to remedial class. His best friends Pierce Aogami (this is a nickname that literally means "blue-haired guy with piercings", his real name is never revealed) and Motoharu Tsuchimikado tease him about how their teacher Komoe Tsukuyomi (who looks like a little girl even though she is most likely in her thirties or forties) has a crush on Touma and thus goes easy on him despite his poor grades, and they wish they were in his shoes. Touma is disgusted that they think a girl who looks like a child is hot. During Komoe's lecture, Touma stares out the window and thinks about Index, wondering if she is okay and if he made the right choice in letting her leave. Aogami accuses him of staring at a girl's tennis game happening outside instead of listening to their teacher. Incredibly hurt, Komoe starts to cry. Everybody in class gets pissed at Touma.After class, Touma grumbles as he walks home. Mikoto runs into him and says she wants to finish their fight from last night. He walks right past her, and she angrily orders him not to ignore her. He comments that she's challenged him to fights so many times in the past and she's never managed to harm him. She counters that he always runs away instead of attacking her, so they need to decide the real winner. She's also offended that despite the many times they've met, he can never remember her name (he nicknames her "Biri Biri", the Japanese onomatopoeia for electricity; "Sparky" in the manga version; "Bug Zapper" in the English dub). She gets so angry that she releases some electricity that damages the surrounding area. Some of Academy City's security robots attempt to apprehend them, so they run.After losing Mikoto, Touma heads home to find three cleaning robots in front of his door surrounding something. He shoos them away, and is horrified to find Index lying face down with a massive slash wound on her back. A man wearing a black longcoat with a barcode tattoo on his cheek walks up and says he is a magician.The man says he and his partner were assigned to capture Index. His partner attacked her with a sword, believing that The Walking Church would protect her and intending to knock her out. To their shock, the sword went right through her habit and horribly injured her. Index managed to escape and staggered to Touma's dorm before passing out. Touma realizes that it was his fault that she was injured, because his right hand destroyed The Walking Church. He then becomes enraged and says he won't forgive the man and his partner for hurting her.
The man introduces himself as Stiyl Magnus, then declares his magic name: Fortis931 - I Prove Why My Name Is The Strongest Here. A magician traditionally only gives his magic name when the situation is serious. In this case, since Touma has seen too much, he can't allow him to live. Stiyl launches a fireball at Touma, but he catches it with his right hand and it instantly goes out. Shocked, Stiyl conjures up a Flaming Sword and swings at him, but Touma grabs it with his right hand and it disappears as well. Touma concludes that his right hand works on magic as well as esper powers. Stiyl says he has no idea how Touma did that; Touma has no magic and Stiyl can't think of any esper powers that could do something like that. However, he is far from defeated and summons his trump card, the fire demon Innocentius, a giant made of 3,000 degree flames. The demon lunges at Touma, but he punches it and it disappears... only to reappear after a few seconds. It forms a massive crucifix of flames and swings it down. Touma catches it, but is nearly brought to his knees by Innocentius' massive strength. Innocentius is so hot that the hallway is catching fire and the door handles are melting. Touma is able to tolerate the heat because of his right hand, but the monster and his weapon are not disappearing. Index suddenly starts talking in a machine-like monotone. She is now in John's Pen Mode, where her mind goes on automatic to retrieve her magical knowledge from the grimoires she read. She explains that to summon Innocentius, special runes must be applied to the surroundings, and as long as the runes remain, it can regenerate indefinitely. Stiyl tries to blast Touma in the back with his flames, but he swings Innocentius in the way and uses it as a shield, then jumps over the railing.Innocentius gives chase, and Touma notices for the first time that the walls are covered with photocopied runes, attached with tape. Touma makes it outside, and the demon can't follow him because the runes are only inside the building. Touma tries his phone, but it doesn't work. He considers running to get help, but realizes it would take too long. He remembers when Index asked him if he would follow her to Hell, and he says he doesn't want to go to Hell for her, so he'll pull her out instead.Stiyl prepares to grab Index and leave, but the fire sprinklers activate. He gets annoyed and comments that his magical flames are designed to not trigger the heat sensors, so Touma must have pulled the fire alarm. He calls out that it's pointless as Innocentius cannot be harmed with such a measly amount of water. Touma appears and says that's not the point. The runes were on paper, and now they are getting wet. Stiyl protests that copy paper doesn't crumple that quickly when wet, but Touma points out the ink would still run. Innocentius appears and attacks, but Touma backhands it in the face and it disappears. Since the runes are gone, it doesn't come back. Stiyl panics and tries to conjure another fireball, but Touma charges up and knocks him out with a punch to the face.After retrieving Index's hood from his room, Touma carries the still bleeding Index away before the firefighters and Anti-Skill (Academy City's main police force) arrive (in the anime version, Mikoto and her roommate Kuroko Shirai are among the bystanders wondering what happened). Touma realizes he can't go to the authorities because nobody would believe a story involving magic. Plus, Index is not an Academy City citizen, and they would wonder how she entered the city undetected. He notes that surely her 103,000 grimoires had some healing spells. Index, still in John's Pen Mode, confirms this, but reminds him that she can't perform magic herself. He can't perform the healing spell because his right hand would just negate it. Furthermore, they can't ask an esper for help. She explains that long ago, espers were naturally occurring. Some normal people got jealous and discovered magic to counter them. Over time, this historical knowledge was all but lost and magic was regarded as fiction by most of the world. Because of differences in how esper powers and magic work, if an esper attempts to use magic or vice versa, he will suffer great damage to his body. Touma thinks and asks if a normal person would be able to perform the healing spell if given the proper instructions. When she confirms this, he says that's good because he knows one person who hasn't gone through the Power Curriculum, his teacher Komoe.
Touma carries Index to Komoe's apartment and knocks. The inside is littered with beer cans and cigarette butts, betraying her real age. Komoe is shocked that he's visiting her and briefly tries to hit on him, but he barges in, clears part of the floor, and lays Index down on her stomach. The teacher is horrified by her injuries and asks why he brought her here instead of the hospital. He says there's no time and asks her to follow Index's instructions exactly. Still in John's Pen Mode, Index asks him to leave the room, or else his right hand would interfere with the spell, so he sadly walks out. Index asks what time and date it is, saying it is important. Komoe, still confused but desperate to save her, says it is July 20, 8:30 PM. Index is surprised because she didn't look at a clock, so the teacher explains that her internal clock is accurate to the second. Nonetheless, Index gets up and checks the position of the stars, only to confirm Komoe is correct. She then draws a pentagram on a table with her own blood. Komoe says this whole thing is crazy and she's going to call an ambulance, but Index says she would bleed out before it can arrive. Index asks her to help place items on the table until it becomes a mini replica of the room they are in. Next, she has Komoe join her in chanting. Eventually, when Komoe accidentally nudges the table, the whole room shakes. Index says the spiritual link was successful. Now, Komoe must imagine an angel, which will arrive and heal Index. Index clarifies that it won't be an actual angel, but a replica molded from mana and shaped by Komoe's thoughts. Komoe has trouble at first, but eventually, the angel comes, heals Index, and dissipates.Index's injuries are healed, but she's still exhausted. She finally gets out of John's Pen Mode and passes out muttering that she's glad she didn't die, or else Touma would have been devastated. Komoe sighs that Touma has attracted yet another girl. She questions Touma about his relationship with Index, and eventually agrees not to report her to the authorities.The next day, Komoe leaves to go shopping, while Touma tends to Index. Index explains that she was from Necessarius, aka The Church of Necessary Evil, an ancient English organization that strove to use magic as a weapon against itself, referencing how historically, the Church condemned witchcraft. When they learned of her ability, they forced her to read the grimoires in the hopes of using her a weapon, but she eventually escaped. Touma gets angry at their cruelty and misuse of human lives and vows to protect her. He then questions why hardly anybody has heard of magic, given that any normal person can learn it. She explains that the Magic Side is very secretive, hording its knowledge and power.Meanwhile, Stiyl and his partner Kaori Kanzaki, a Japanese swordswoman, spy on them. Stiyl asks if she found anything on Touma. She replies that according to Academy City's records, Touma is a Level 0, a loser with no future, but that doesn't make any sense given what he can do. Since Index is fully healed, they must have gotten someone to do a healing spell for them. Kaori comments on Stiyl's defeat, and he replies that he's learned from it. He's mass produced his runes on cards now, and laminated them so they can't be destroyed by water. Stiyl sadly comments on how Touma and Index look happy together, and now they will have to take that away. Kaori comments that he used to be in Touma's shoes.Since Touma's apartment was burned, Komoe allows him and Index to stay in hers for the time being. When he asks Index to tell him a little about herself, she says she has no memories from before one year ago. One year ago, she woke up on the run, knowing only about the 103,000 grimoires and of Necessarius. He gets angry, thinking they must have hurt her and given her amnesia. However, Index misinterprets his attitude and thinks he's angry at her. He tries to explain himself, but she bites him and then leaves to join Komoe at the public bathhouse. He tries to follow her to apologize, but is shocked when he notices there is nobody out in the street, making the area look like a ghost town. Kaori appears and introduces herself.
She explains that Stiyl set up some runes in the area that created a people-clearing field, which causes bystanders to subconsciously turn away from the area and be unable to see or hear what happens inside, so nobody can interfere. Touma is slightly struck by her beauty and her outfit: cowboy boots, jeans with the left leg cut off, and a tied off t-shirt that makes it clear she's not wearing any undergarments. The fact that she's Stiyl's partner and she's carrying a two-meter long nodachi gives him pause. In the light novel version, she briefly comments on how the kanji for Touma's name can translate to "The One Who Purifies God And Exorcises The Devil". Kaori says if he will hand Index over to her peacefully, she will spare him. He refuses, so she demonstrates her prowess by swinging her sword and slicing apart a wind turbine in the distance. She says if he doesn't give up, she will reveal her magic name and kill him. He charges, but she halts his advance by swinging her sword once, creating seven slashes in the asphalt. She calls this attack "Nanasen", and repeats that she does not enjoy killing, but she will if forced to. There is nothing he can do, because she's too fast for him. Touma steels himself and in his head, says he still has a chance if he can catch her sword with his right hand. He charges, and she swings her sword. He screams as his right hand and arm get really bloody, and he realizes he made a mistake. He squints and sees that Kaori has seven razor sharp metal strings around, controlling them like a puppeteer. Kaori confirms that this is how Nanasen actually works. Neither the wires nor the sword are magical, so Touma's right hand could not negate them. He has no chance of winning, so he has no choice but to give up. He refuses, so she kicks him down and rams her sword's scabbard into his gut.She explains that she and Stiyl are from Necessarius, and that Index was once their best friend. Touma calls bullshit on this, given how she must have been the one who slashed her back open earlier. She retorts that she had no idea The Walking Church no longer functioned, and she deeply regretted it. She says they need to retrieve Index now, or else she will die soon. He asks what she means, so she explains that 85% of her brain is filled up with the 103,000 grimoires, leaving 15% for memories. When her brain is filled to capacity after about a year, a sure thing because of her photographic memory, she must have her memories wiped before she dies from the strain. This has happened year after year, and it breaks Stiyl and Kaori's hearts every time. Her year limit will be up in three days.Touma asks why they didn't just confront Index and reintroduce themselves, instead of presenting themselves as enemies after her knowledge. Kaori goes berserk and proceeds to beat the shit out of him. She screams that he has no idea what it was like. They did try that a few times, even using pictures, but the fact that she didn't remember them was too much. They had to stay separate from her because they now can't even bear to see her smile. He says that's no excuse and that they didn't even consider Index's feelings. If he was in their shoes, he would have never given up and would have tried to find a way to make her memory erasure unneeded. She swings her scabbard, but he catches it and punches her in the face. However, it has no effect and he passes out from his injuries. She is shaken up by his words. In the anime version, after Stiyl removes the people-clearing field, Mikoto and Kuroko look at the damage to the windmill and road and wonder what happened.Touma wakes up in Komoe's apartment, heavily bandaged. Index tells him Komoe found him lying in the middle of the road and carried him back, and the two of them had been tending to him. He's been asleep for three days, causing him to panic when he remembers Kaori's warning. Index is miserable because he got hurt for her sake. Suddenly, Stiyl and Kaori appear at the door. Since Komoe doesn't know who they are, everybody plays along that they are all friends until she leaves. Index tells the two that she will go with them if they promise not to hurt Touma, but they say they are not there for that. They tell Touma that the memory-erasure spell can only be performed around midnight, so they will leave them alone until then. They trust that Index won't leave because she won't abandon him. Touma says he will find a way to save Index so she won't have to have her memories erased, and they say he's welcome to try, but if he can't, they will perform the spell, end of discussion.
Index falls unconscious with a horrible headache. Throughout the day, Touma looks through Komoe's various textbooks for anything involving memory. He also calls several research facilities, but most of them are closed and the others hang up on him, thinking he's a prank caller. He tries to call Komoe, but she's relaxing at the bathhouse. Midnight rolls, and the two magicians return. Touma begs them not to do it, but Stiyl calls him out and points at how much pain Index is in. They have to erase her memories or else she will die. Kaori takes pity on Touma and tells Stiyl that they can wait until 12:15 to do the spell without endangering Index. Touma deserves the chance to say goodbye. Stiyl grudgingly agrees and they step outside. Index briefly wakes up, still worried about the magicians hurting Touma. He promises that they will all make it through this and he will never fail her again. She passes out again.Touma laments not being able to do anything, but realizes something: if 15% of the brain holds one year of memories, then a person with photographic memory would only live to be about 6 or 7, and that is clearly not the case. Furthermore, where did Stiyl and Kaori get 85% and 15% from? He concludes that Necessarius tricked them, relying on their ignorance on how the brain works. He calls Komoe again and finally reaches her, then asks about photographic memory. She confirms that the human brain has infinite capacity, and a person with a perfect memory will never "overload". In addition, personal memories and knowledge are stored in different areas of the brain, so those numbers have no basis in fact. He thanks her and hangs up. He guesses that Necessarius put a curse on Index that causes her to suffer unless her memories are erased each year, in an effort to stop her from leaving or turning against them.He touches her on the head with his right hand, but nothing happens. Determined, he starts touching her all over, then worries if he might have to touch her some place inappropriate. He opens her mouth and finds a rune on the back of her throat. He reaches in and touches it... and is blown back by an explosion of power as the rune is destroyed. Index goes into John's Pen Mode and floats in the air, glowing. Stiyl and Kaori enter the room and are shocked to see Index using magic. In her monotone, she says the "collar" has been destroyed and cannot be repaired, so the first order of business is to eliminate the threat that destroyed it. She says Touma's right hand cannot be analyzed, so she will go for sheer power. She fires a magical laser called St. George's Sanctuary. Touma blocks the attack with his right hand, but is nearly blown away, and like Innocentius, the beam is continuous and doesn't instantly disappear. While holding back the beam, Touma tells the other two that obviously, their superiors lied to them: Index can use magic and she was not in any danger of her brain overloading. Touma's strength is almost spent, but Kaori uses her wires to trip Index and knock her on her back, causing the beam to destroy the roof and take out the Academy City satellite Tree Diagram in orbit.
White feathers start floating down from the hole in the roof. Horrified, Kaori tells the other two that this is the spell Dragon's Breath. If a feather comes in contact, it could be lethal. Index gets up and fires the laser again, but Stiyl quickly throws his rune cards around, summons Innocentius, and uses it as a shield. However, Index analyzes Innocentius and adjusts the laser so it will be vulnerable to it. As the fire demon slowly dissolves, Stiyl yells at Touma that this is their last chance. Touma charges up and touches her on the forehead. She instantly drops out of John's Pen Mode and passes out. Touma cradles her in his arms, relieved. Stiyl and Kaori shout a warning and try to get to him, but it's too late. One of the feathers lands on his head and he falls over, as if he were dead.Stiyl, Kaori, and Index take Touma to the hospital, where a doctor named Heaven Canceler (who is implied to know about the Magic Side) treats him. Stiyl and Kaori hand the doctor a letter to be passed to Touma when he wakes up, then leave. Index impatiently snatches the letter and reads it. The letter is Stiyl grudgingly thanking Touma for saving Index, and thanking him for letting them know that they were being lied to by their superiors. They are going back to England to confront them, and will leave Index in his care for the time being. The final part says the letter self-destructs shortly after being read. She throws it away and it bursts into pieces.Heaven Canceler tells her she is free to visit Touma, but warns that based on the brain damage he took, he may have suffered memory loss. She enters his room and is elated to find he is awake, but he asks her who she is. She frantically introduces herself and describes some of their experiences from the past few days, but nothing rings a bell. In tears, she declares her love for him and begs him to remember her. Suddenly, Touma laughs and says she fell for it. As she's stunned, he explains that he did lose his memories, but since it was caused by magic, all he had to do was touch his head with his right hand and they were restored. He also names his strange ability Imagine Breaker. Enraged that he made fun of her, she bites him several times and storms out.Heaven Canceler walks in and says he could tell Touma was lying. He sadly admits it, but he had to lie because he didn't want her to cry anymore. The doctor apologizes, because brain damage is one of the only things he can't fix, so Touma's memories may be lost forever. Touma says that doesn't matter, and they are still in his heart.