Aria the Scarlet Ammo is a Japanese light novel. Kinji Tōyama is a student at Tokyo Butei High, a universal educational facility. At this school, students undertake special training in order to learn the path of the Butei, which is a national qualification permitting its holders to arm themselves and capture criminals. The Butei were established to counter the worsening crime conditions, with training in various specialized fields. One day, Kinji decides to quit the Academy, until he is mysteriously attacked by the Butei Killer, a notorious criminal hunting down Butei with passion.