The third season of the Bungo Stray Dogs anime television series is produced by Bones, directed by Takuya Igarashi and written by Yōji Enokido.

The first three episodes of the season are based on a light novel prequel that shows how Osamu Dazai met Chuya Nakahara while working for the Port Mafia, while the remaining episodes follow the manga's storyline with the Detective Agency and the Port Mafia being manipulated by a group known as Rats in the House of the Dead.

As things have died down after the battle with the Guild, the Armed Detective Agency relaxes at a café on the first floor of their office building.

Atsushi reports that criminal organisations have arisen to find the rumoured Guild's fortune and how he encountered Lucy the other day.

In an attempt to protect their daughter, her mother, who was the wielder of Demon Snow at that time, ordered it to kill herself and passed on the ability to Kyouka.