Tohru Kuroe is caught in the middle of a terrorist attack that claims the lives of all his classmates. Fearing the prospect of losing another woman, Tohru seizes an abandoned gun and unleashes the beast within. When he regains his senses, Tohru realizes he has become a killer. He discovers that he was genetically created as a lethal weapon and designated as D-17. Tohru struggles to maintain his regular life while confronting threats to his safety and the lives of those in his circle.