Episode 21

Double Black (つの黒,) is the 21st episode of Bungo Stray Dogs anime series. It first aired on November 26, 2016.

Synopsis
The leaders of the Agency and the Port Mafia negotiate an alliance. Meanwhile, Dazai and Chūya face off against Lovecraft.

Summary
Fukuzawa is seen strolling at a park and tries to offer a fish to a cat when he is approached by Atsushi.

At the Agency's office, Kunikida berates Dazai for his laziness to which Dazai tells him that the boss lined him up for a new job. They are then interrupted by Fukuzawa, who asks if Dazai has planned to meet with the Port Mafia. Kunikida is confused about why Dazai can do such a thing. Dazai tells him that it is Atsushi's idea. However, still confused about what's happening, Kunikida asks Dazai why he is responsible for arranging the meeting. Dazai reveals that he is originally from the Mafia, while Kunikida is shocked by the reveal.

At the Mori Corporation, Mori together with Chūya look at the casualties caused by Q's curse. Shortly after, Kōyō arrives, telling Dazai has kicked her out to run an errand for him. She then invites Mori from the Agency's boss, who reminisces about when he killed the previous boss of the Mafia, having Dazai as his witness in his succession as the next boss.

Mori, who is accompanied by Black Lizard, arrives at the meeting place, which Dazai then welcomes. Shortly after, Fukuzawa shows himself, accompanied by Kunikida. Fukuzawa soon tells Mori that the alliance with the Mafia is his subordinate's idea; however, he refuses as the idea of cooperating with criminals goes against the Agency's standards.

On the other hand, Mori refuses to have a ceasefire between the organizations, stating that the party who trusted the agreement would be the only one to suffer. During the meeting between the two bosses, they try to attack each other to settle the dispute between the organizations. It turns out that the Fukuzawa Mori meet is an illusion projected by Tanizaki. After the meeting, Fukuzawa orders Mori not to get in their way as they will be retrieving Q. They eventually tentatively agree to a temporary ceasefire after a minor skirmish between the bosses, which is shortly disrupted by Mori's decision to send Chūya.

Dazai is sent to recover Q, with the surprised assistance of Chūya sent by the Port Mafia. The two wipe out the Guild members protecting Q, with Mori saying that the "Twin Dark" has revived for the night. As the two return to the surface, they are attacked by Lovecraft. The two seemingly defeat Lovecraft before he changes into an eldritch monster, causing them to have to use Corruption. The rampaging Chūya can defeat Lovecraft at the cost of injuring his own body, to the shock of Steinbeck. In the end, Dazai nullifies Chūya's Corruption.