The story takes place in Tokyo Butei High School, a school where aspiring individuals, known as "Butei," are trained in firearm handling. Kinji Tooyama, a second-year student, possesses a distinct ability, which he keeps hidden to live a peaceful life. However, on his way to school, he becomes unintentionally involved in an explosion and encounters H. Aria Kanzaki, a skilled Assault Studies S-Rank Butei.