Tokyo Butei High School is a special school where armed detectives, also known as Butei, are trained and educated. Tooyama Kinji is a sophomore student, who can go into Hysteria Mode when "stimulated" - affecting his mental state (ultra-fast reflexes, protection complex) and manner of speech. He tries to hide this genetically inherited ability from others in order to live a peaceful life. But when he becomes the victim of a bombing incident, by a Butei Killer copycat, his quiet days are over with the fateful encounter with Kanzaki H. Aria - the Butei High "Assault" department elite.