Touma Kamijou just can't catch a break. He might live in Academy City, a place full of more super powered students than you can shake a stick at, but his only superpower is his supernatural lack of luck. He wants nothing more than to keep a low profile, but when a girl named Index comes into his life, it gets more complicated and dangerous than ever!

The horrifying experiment to make Accelerator into an all-powerful Level Six has commenced--and it involves the wholesale slaughter of the little sisters cloned from Mikoto Misaka. Can Touma find a way to stop the seemingly invincible Accelerator? Could it be that weakness is stronger than strength could ever be?

Mikoto Misaka is a Level Five esper--one of the most powerful in Academy City. She's so powerful, in fact, that her DNA has been harvested to create a series of clones--the "Sisters." But who is behind these clones, and why would they go to such lengths? The sinister truth is nothing she or Touma could have imagined, and it involves the terrifying Accelerator, the most powerful esper of all time!

In London, the women's dorm in a magicians' base get wild, while in the underbelly of Academy City, Accelerator stumbles upon someone who has been waiting for him all this time.

In the final battle against the Accelerator, the truth cuts like a knife, while romance blossoms between Misaka and Touma. Meanwhile, Tokiwadai Middle School welcomes its newest student, the egotistical Kongou Mitsuko, who immediately sets off a power struggle among the student body as she seeks to form her own faction. While tensions run high at the school, what better time than to throw a sports festival? It may sound like all fun and games, but Academy City is about to see an explosive competition the likes of which it's never known before!

Item’s battle comes to a head as their hideout is raided, and the team reaches its breaking point. Disgusted with Mugino’s disregard for the other members’ lives, Hamazura finds the resolve to stand up to her. Mugino may be a Level Five, one of the strongest espers in Academy City, but she’ll see that even a powerless Level Zero like Hamazura can put up a fight when his back is against the wall!

Throughout Academy City, the rumors are spreading like wildfire. People are finding mysterious envelopes containing free cash cards in and around the back alleys of the Seventh School District. Whipped up into a frenzy, the populace looks for as many cash cards as they can get their hands on, even if it means braving the perilous Skill-Out Territory, risking injury or worse by roving gangs of Level 0 thugs. Judgement is left with no choice but to step in... While Shirai and Uiharu try to crack the case and figure out who is behind the cash card chaos, Misaka decides to take to the streets herself... and soon gets embroiled in a disturbing scientific conspiracy the likes of which will rock her world to the core.