Atsushi Nakajima is at the end of his rope when he witnesses Osamu Dazai's latest suicide attempt. Dazai introduces him to the Armed Detective Agency.
Atsushi goes to the Agency's offices with Dazai, but his self-confidence is so low that he thinks about quitting -- until an emergency arises.
Atsushi takes his first case with Jun'ichirō Tanizaki and his sister, Naomi. It's an easy assignment in Yokohama, but that's Port Mafia territory.
Traumatized by Akutagawa and Higuchi, Atsushi blames himself for events in Yokohama. Meanwhile, Ryurou Hirotsu and the Black Lizard are on the move.
Atsushi accompanies Ranpo Edogawa, self-proclaimed greatest detective in Japan, on a murder investigation despite being skeptical of Ranpo's skills.
Kunikida and Dazai investigate a series of disappearances in Yokohama. The hacker Taguchi believes they're linked to the shadowy "Azure Messenger."
As the Agency scrambles to investigate the Azure Messenger's bomb threat, Dazai interviews Sasaki, the only survivor of the hospital raid.
Despite his worries about Dazai, Atsushi accompanies Akiko on a shopping trip. But their outing turns bloody when Port Mafia attacks their train.
Atsushi and Kunikida try to figure out Kyoka's ability and history with Port Mafia. Kunikida wants to turn her in, but Atsushi can't bear to do it.
Dazai's old partner, Chuya Nakahara, confronts him, demanding to know why he let himself be captured. Meanwhile, Atsushi faces Akutagawa again.
Kyoka asks Yukichi Fukuzawa to allow her to join the Agency. Higuchi grapples with her place in Port Mafia now that Akutagawa is in a coma.
Francis Scott Fitzgerald and the Guild reveal themselves at last. Fukuzawa refuses their offer to buy out the Agency, but Fitzgerald isn't dissuaded.
Dazai's past as a member of the Port Mafia is revealed, along with his friendship with fellow members Ango and the low-ranking Oda Sakanosuke.
Dazai strategizes a plan against Mimic, a powerful guerrilla organization that escaped to Japan after committing atrocities abroad.
As the conflict with Mimic intensifies, the top leadership of the Port Mafia orders its ranking members to initiate an all-out war.
Dazai desperately tries to persuade a suicidal Oda from fighting. Meanwhile, the true intentions of the factions involved come to light.
While working on her first mission with the Armed Detective Agency, Kyoka is attacked by the Port Mafia and the Guild, inciting a three-way war.
Ogai Mori, the leader of the Port Mafia, sends a letter to the Guild, threatening to destroy their prized ship and personnel.
The Guild's Steinbeck and Lovecraft attempt to abduct Agency members Haruno and Naomi. Meanwhile, Dazai is given a dubious offer from the Port Mafia.
With members of the Guild severely injured, leader Fitzgerald enacts an emergency plan in order to protect those under his command.
As the Guild becomes a legitimate threat, the leaders of the Port Mafia and Armed Detective Agency meet to negotiate an alliance.
The Guild's Edgar Allen Poe challenges Ranpo Edogawa to a detective game, offering a reward that is beneficial to the Armed Detective Agency's cause.
As the Guild's massive airship heads on a crash course with Yokohama, the Armed Detective Agency dispatches Atsushi to infiltrate and take control.
With the fate of Yokohama at stake, Atsushi and Akutagawa confront a full powered Fitzgerald atop an out of control Moby Dick.