A certain unlikely hero...No one was able to stop Second Princess Carissa's plot in time, so the worst has come to pass: London has fallen. The city of magic, home to the English Puritan Church and Index, now rests in the hands of the Knight faction. Soldiers control nearly every critical part of the country, commandeering the very streets of the capital. Still, the Puritan sorcerers haven't given up the fight just yet!As the battle for the UK rages on, Touma heads to Folkestone to save Index-only to run straight into the coup d'état's mastermind herself! Worse, Acqua is still alive, and his holy sword, Ascalon, is pointing not at Touma but at Carissa!

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 latest clash of magic and science in Academy City is leaving bodies strewn across the streets! As Accelerator takes on Amata Kihara and the secret ops team known as Hound Dog, an intruder from the Roman Orthodox Church-Vento of the Front-infiltrates the city to crush Touma and his Imagine Breaker. With Touma and Accelerator fighting for their lives, will their paths converge and turn old enemies into erstwhile allies?

Touma has been called out by Mikoto to fulfill his punishment, but can anyone call taking pictures together and getting matching cell phone straps "punishment"...? The arrival of Mikoto's "little sisters" makes their "battle" even more fraught!

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?