Wall Maria falls to the Titans. A young man from Wall Sina enlists in the 104st Training Corps, driven to make change for the sake of humanity. But he didn't expect to catch the eye of a blonde haired cold eyed girl named Annie, who carried a terrible secret. While he carries his own secret.

Alex Mercer didn't know what would happen when that vial broke and the liquid seeped into a wound he had gotten from the shattered glass. After the Colossal Titan's first appearance and some time he decided to enlist. There he met Annie Leonhart, Reiner Braun, and Bertolt Hoover, when the vial broke he wasn't himself, so when the 3 told him of their mission he agreed to go along.