After being ousted from his orphanage due to suspicions about a mystical tiger haunting the place, 18-year-old Atsushi Nakajima finds himself adrift in the city. A chance encounter with the peculiar Osamu Dazai, a man fixated on death and the supernatural, leads Atsushi to an unexpected partnership in unraveling the mystery of the tiger. Teaming up with Dazai's logical associate, Doppo Kunikida, Atsushi delves into a world of strange occurrences and dangerous tasks as part of their supernatural investigation agency. Bound by circumstance, Atsushi navigates this new chapter alongside a cast of enigmatic colleagues, each with their own cryptic pasts.