Welcome to Nanba, the world's largest, most impenetrable prison. Locked away in cell block 13 are four inmates who provide more than enough trouble for Officer Hajime. Between attempted breakouts, gambling, and general misbehaving, these four believe that just because they're in prison doesn't mean they can't have fun! Follow the hijinks of Jyugo, Uno, Rock, and Nico as they pass time behind bars.