For weeks, Atsushi Nakajima's life at the orphanage has been marred by a mystical tiger that only he seems oblivious to. Suspected as the cause of these strange occurrences, the 18-year-old finds himself abruptly cast out of the orphanage, thrust into a world of hunger, homelessness, and aimless wandering through the city.
While starving on a riverbank, Atsushi becomes a savior when he rescues Osamu Dazai, a peculiar man with an affinity for contemplating suicide and a knack for supernatural investigations. Dazai has been on the trail of the very same tiger that has plagued Atsushi's existence. Joined by Doppo Kunikida, Dazai's partner, they unravel the mystery surrounding the tiger. However, the resolution of the case propels Atsushi into a precarious situation.
As a series of peculiar events unfold, Atsushi finds himself coerced into joining their unconventional team of supernatural investigators. Tasked with handling cases too extraordinary for the police to handle, he becomes entangled with a group of enigmatic co-workers, embarking on a journey filled with unusual circumstances and secrets waiting to be unraveled.