"Ouroboros" is an ancient symbol that depicts a snake eating its own tail - meaning infinity. Based on a popular comic, a clumsy detective and a cool gang stand up to true evil. Ikuo and Tatsuya grew up in a children's orphanage together. When their favorite teacher, Yuiko, is murdered, a policeman wearing a gold watch covers up the incident. Ikuo and Tatsuya promise each other to avenge their teacher someday. Twenty years later, Ikuo is a detective in Shinjuku second police station investigating various cases with elite detective - Mizuki, while smart and handsome Tatsuya has become one of the top members of a gang group.

Eiji Arima is a veteran detective who is about to retire. Shoichi Sera is a young lawyer and Misuzu Haruna is a prosecutor. These three people belong to the Gohan Taisakushitsu ("Misjudgment Countermeasure Office’". Their job is to re-examine death-row convictions and check to see if anyone was falsely convicted.