The Twin Darkness is the 31st chapter of the Bungo Stray Dogs manga.
Osamu Dazai and Chuya Nakahara are forced to work with each other to save Yumeno Kyusaku and his doll—as Ougai Mori put it, a revival of the tandem Twin Dark, just for that night. When they managed to get Q and his doll, Lovecraft and Steinbeck were there. Dazai and Chuya fought Lovecraft and Steinbeck, thinking it was easy to defeat the two. But they learned that Lovecraft was actually not an ability user and transformed into a monster. Leaving them with no choice, Chuya used the true form of his ability: Corruption. Even after Chuya defeated Lovecraft, Chuya continued to berserk, but was stopped easily when Dazai grabbed Chuya's wrist, returning him to his normal state.