Expelled from the orphanage, Atsushi Nakajima finds himself in dire circumstances without food or shelter. But his luck changes when he saves Osamu Dazai from drowning. Dazai and Doppo Kunikida work for the Armed Detective Agency, a team that tackles cases beyond the reach of authorities. Atsushi agrees to help them find a mystical tiger causing chaos in the region, despite Kunikida's reluctance. After the team resolves the problem, Dazai invites Atsushi to join the agency. But their mission becomes risky when the infamous Port Mafia targets them in a fight for control. To keep his city and new friends secure, Atsushi must learn to use his new abilities effectively.
