A mystical tiger has been sighted at the orphanage where Atsushi Nakajima resides, yet he remains the sole individual unaware of its visits. Accused of the strange events, the 18-year-old Atsushi is expelled, left hungry and homeless as he roams the city. While starving by a river, Atsushi rescues a peculiar man named Osamu Dazai, who was attempting to drown himself. Dazai, an eccentric detective obsessed with suicide and the supernatural, had been tracking the very tiger haunting Atsushi. Together with Dazai's partner, Doppo Kunikida, they uncover the truth behind the tiger's appearances, dragging Atsushi into a complex situation. As more bizarre incidents occur, Atsushi is compelled to join Dazai's agency of supernatural investigators, tackling strange cases beyond the reach of ordinary law enforcement alongside his equally mysterious coworkers.

In this installment

Each evening, Osamu Dazai, the youngest senior executive of the Port Mafia, meets with Sakunosuke Oda, the lowest-ranking member, and intelligence officer Ango Sakaguchi at the Lupin Bar to unwind and share camaraderie, regardless of their differing ranks within the organization. One night, Ango suddenly disappears, leaving behind only a photograph of the trio. In the present timeline, Dazai has joined the Armed Detective Agency. The American gifted group known as the Guild aims to revoke the Agency's license, compelling Dazai to face threats from both the Guild and the Port Mafia, as both factions seek to dismantle the Agency.