A Certain Magical Index, Vol. 20 (light novel) — Kazuma Kamachi

A certain unlikely hero...
October 18-World War III has begun. As the flames of conflict between Academy City and Russia spread further, the rest of the world suddenly finds itself pulled into the fight. Fiamma, the only remaining active member of God's Right Seat, attempts to control everything from the shadows while others run straight into the heart of the firestorm to do what the can!
Kamijou will travel as far as he must to revive the magically comatose Index. Accelerator won't let even a war stop him from saving Last Order. And Hamazura must find a way to heal Takitsubo's stimulant-riddled body. Though their goals are different, fate will force these three to cross path in Russia where something sinister lies in wait for them...!