Chiwa has been dreaming of returning to the Underground since he was young. He's finally succeeded by joining the Special Forces unit of the police. "Great Raven" is made up of mostly Enhanced Humans and their unique abilities. Their mission is to track down members of the crime syndicate, Joker, and stop it from kidnapping and altering children's bodies. But Chiwa is surprisingly unprepared for the things he finds in the Underground...

Following the first-year high-school student, Arisugawa Hikaru, comes a tale of Gaitou: a thief who only appears in dreams and steals the darkness inside of people's hearts. Hikaru, one of the Gaitou, hunts down Gai rabbits, one of the lower-class demons that seek the darkness in humans. With the aid of his companion, Ban, Hikaru protects people from falling into despair, however, the game has yet to begin.