Sword Art Online 25 (light novel) — Reki Kawahara

READ THE NOVEL THAT IGNITED THE PHENOMENON!
Kirito's chance encounter with Eolyne, a man who bears a heart-rending resemblance to Eugeo, shakes him to his core. But now is no time to be sentimental. The fires of interworld war are being lit one by one, and the peaceful days in the Underworld may be numbered. Elsewhere, the decisive battle against Mutasina of the Virtual Study Society looms, and to make matters even worse, she's used her powers to take a battalion of one hundred mages under her command! Can Kirito and company devise a strategy to defy their overwhelming disadvantage before time runs out...?