For weeks, the orphanage of Atsushi Nakajima has been afflicted by a supernatural tiger that only he appears to be aware of. The 18-year-old is abruptly booted out of the orphanage and left hungry, homeless, and roaming across the city after being suspected of being behind the unusual happenings. Atsushi saves a somewhat eccentric man called Osamu Dazai from drowning while hungry on a riverside. Dazai, a wacky suicide enthusiast and supernatural detective, has been looking into the same tiger that has been harassing the youngster. They solve the riddle with Dazai's companion Doppo Kunikida, but the outcome puts Atsushi in a bind. As strange incidents occur, Atsushi is persuaded into joining their firm of supernatural investigators, taking on unique cases that the police cannot handle.