October 30. Eleven days have passed since World War III begun. Academy City continues to show its presence in the Elizalina Alliance of Independent Nations and in domestic waters alike. As Russia's threat is kept in check by the technologically-superior Academy City planes, Kamijou Touma and Lessar begin their advance in the snowy fields of Russia to expose the magical war Fiamma of the Right has concealed behind the alliance between the Roman Catholic Church and the Russian Orthodox Church. Elsewhere, after escaping Academy City, Hamazura Shiage and Takitsubo Rikou attempt to survive the war while looking for a bargaining chip that Shiage can use to negotiate with Academy City. Meanwhile, the appearance of Aiwass exerted great strain on Last Order's body, forcing Accelerator to follow the mysterious being's advice and go on a journey to Russia to look for a way to cure Last Order's condition.
In order to foil Fiamma's plan, Touma and Lessar head to the Elizalina Alliance to secure Sasha Kreutzev, but Fiamma manages to defeat them, as well as Elizalina and Vento of the Front, and retrieves Sasha. Shiage is faced with a problem as Rikou's condition worsens, and a man named Digurv agrees to help Shiage by taking Rikou to a clinic in a nearby town. The town, however, is attacked by privateers hired by the Russian army. Accelerator intercepts a delivery of parchment and follows it to an air base. Here, he and Last Order are ambushed by Academy City forces, especially a Third Season clone named Misaka Worst.
Shiage and Rikou manage to survive the onslaught of the privateers with the help of a mercenary who introduced himself as Acqua of the Back. Meanwhile, Touma and Accelerator clashes during a moment of the latter's despair, and it triggers a fight that is difficult to explain. Accelerator loses, but is later brought with Last Order to the Elizalina Alliance, where a memo with the words "Index Librorum Prohibitorum" is left by his side.
Eventually, news of Russia using the Kremlin Report sends shockwaves to the Russian pilots fighting in the Sea of Japan. The Pope finally wakes up from the injuries he received after a surprise attack by Fiamma of the Right. Two supersonic bombers are hijacked by two Level 5s, Mugino Shizuri and Misaka Mikoto. The resolve of the Russians who support Fiamma is starting to waver. An angel made of AIM diffusion fields, Kazakiri Hyouka, manifests to protect her friends. Stiyl Magnus prepares to fight Index who is under Laura Stuart's control. Finally, Touma gathers his thoughts one more time before marching towards Fiamma of the Right.
- Anime: Toaru Majutsu no Index III Episode 21
- Manga: N/A