A certain unlikely hero...Fiamma’s plans have finally been set in motion. His ultimate creation, the massive Star of Bethlehem, dominates the skies over Russia. Now he stands ready to purge everything and everyone unnecessary to his grand mission to save humanity. Down below, sorcerer, soldier, and student alike are fighting for their lives against a new calamity that threatens the entire world. After following Fiamma so far for so long, Kamijou knows that there’s only one way to put an end to this crisis: Defeat Fiamma and destroy his flying fortress—even if it means challenging God’s Right Seat all alone. Rotten luck or not, Kamijou has to do it. After all, Index is still waiting for him...!

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!

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.

Seven days have passed since the start of the Daihasei Festival, one of the biggest events of Academy City. Everyone is participating--Seiri Fukiyose is helping coordinate the games, Komoe Tsukuyomi dresses for the part as she cheers for her students, and of course, famous Mikoto Misaka is blowing away the competition. Even Kamijou has appearances! But a shadow has fallen across the celebrations: The Croce di Pietro. This magical artifact threatens the livelihoods of everyone Kamijou holds dear so he dashes off to try and bring Academy City back from the brink. But Oriana Thompson, the magician known as Route Disturb, and the Roman Catholic Church are determined to bring the bastion of science to its knees. Kamijou is going to need all the help he can get-and some luck for once wouldn't hurt!

Showdown in Castle Town! Having successfully averted the airship attack, Satou and company arrive safely in the royal capital. There, they are reunited with Nana’s “sisters”—Numbers 1 through 8—and give them the gift of a lifetime. But as is tradition with every trip to the capital, Satou must rub elbows with the aristocracy before he can enjoy his sightseeing. He even receives a surprise visit or two, including a summons from Sir Juleburg of the Eight Swordsman of Shiga! Because no leisurely trip would be complete without a friendly duel…

Violence rages through the streets of Avignon as magic and science clash! Academy City forces are bombarding the city, and Touma has to find the weakness in Terra of the Left’s spell, Light’s Execution, before it’s too late. With all eyes on France, there’s no one watching as the shadow organizations of Academy City rise up, thrusting Accelerator and the rest of Group into a deadly battle royal!

Fiamma of the Right, last remaining member of the shadowy Roman Orthodox organization, God's Right Seat, has finally set his long-awaited plans into motion. The Star of Bethlehem: a giant fortress rises into the wartorn Russian skies. Fiamma calls for a purge of the unworthy while three young men continue to fight, carrying various causes in their hearts as they make a last stand against impending disaster.