After returning to the present, the season introduces its primary antagonist: , leader of the "Rats in the House of the Dead".
: Ultimately, Atsushi Nakajima and Ryūnosuke Akutagawa are forced to combine their powers to defeat Fyodor's subordinate, Ivan Goncharov, while Dazai outmaneuvers Fyodor on the intellectual battlefield. Production and Technical Highlights
: Fyodor infects both the Armed Detective Agency’s leader, Yukichi Fukuzawa , and the Port Mafia’s leader, Ōgai Mori , with a "Cannibalism" virus.
Season 3 opens with a three-episode adaptation of the light novel prequel. Set seven years before the main story, it explores the chaotic "Dragon’s Head Conflict" and the first meeting between and Chūya Nakahara .