Chūya Nakahara and Osamu Dazai vs. John Steinbeck and Howard Phillips Lovecraft

Chūya Nakahara and Osamu Dazai vs. John Steinbeck and Howard Phillips Lovecraft is a battle fought between the Port Mafia's infamous former Twin Dark Chūya Nakahara and Osamu Dazai against the Guild operatives John Steinbeck and Howard Phillips Lovecraft during the three-way gifted organizational conflict.

It happened outside a shack where the Guild holds Kyūsaku Yumeno after being captured by Lovecraft.

Prologue
Though the Armed Detective Agency president Yukichi Fukuzawa and the Mafia boss Ōgai Mori fail to agree in forming an alliance against the Guild, Mori nonetheless recognizes a sound logic behind striking an alliance. Thus, he sends his executive Chūya to aid Agency member Dazai in retrieving Q from captivity, hence resurrecting the notorious duo Twin Dark for that night.

Battle
When Dazai arrives at the shack, Steinbeck, Lovecraft, and various Guild operatives surround him at gunpoint. Dazai realizes falling into their trap, while Steinbeck mentions how their tactician is quite talented in predicting their enemies' moves. In that moment, a boulder is hurled towards Lovecraft from above courtesy of Chūya, who soon repels the Guild's gunshots using his ability. Chūya then expresses his distaste towards working with Dazai, who also thinks likewise.

Steinbeck admits that Chūya's ambush has not been foreseen in their strategy and summons grapevines from his palm, only for Dazai to nullify his ability by touching his shoulder. Chūya then delivers a kick at him, after which the two further voice out their mutual hate in collaborating with each other.

After reliving their former hostile partnership in the Mafia, Dazai and Chūya locate Q, whom they mutually prefer to have killed out of grudge. However, Dazai cuts off their restraints and keeps them alive as insurance that the Mafia does not kill him in case his nullification ability is needed to be used on Q again.

Upon exiting the shack, Chūya's neck gets entangled in Lovecraft's tentacle, who recovers from taking the boulder earlier and has activated his partial eldritch form. He hurls Chūya towards a wall, to which Dazai praises Lovecraft's incredible strength. Dazai assures Chūya that he can easily nullify the tentacles once they come in contact with him, but he is sent flying when Lovecraft hits him with his tentacle. Chūya punches another incoming attack and rushes towards Dazai.

Realizing that he is badly hurt, Dazai concludes that Lovecraft's tentacles are not an ability, leaving them no choice but to use their past battle strategies. Settling with combat code "Shame and Toad", Dazai acts as a decoy to lure in Lovecraft, after which Chūya appears from behind Dazai and lands a gravity-enhanced punch that punctures Lovecraft. He then controls his gravity to have him stay on the ground until morning.

However, Lovecraft transforms once more, and his tentacle instantly hacks off Dazai's bandaged arm, detaching it off with him in his full gigantic eldritch form. Chūya dashes towards Dazai and worries about his severed arm, only for Dazai to release his hidden forearm from his coat, annoying Chūya. Dazai recommends using Chūya's Corruption as their last resort, to which Chūya begrudgingly agrees. Chūya activates his ability's ultimate form and engages Lovecraft, who regenerates his limbs whenever Chūya hits him with his projectiles.

Holding Steinbeck at knife-point, Dazai questions him about Lovecraft's weakness. Steinbeck refuses to cooperate but inadvertently mentions that his partner cannot be destroyed from the outside, giving Dazai the assertion that he may be damaged from inside. Dazai detonates a bomb hidden in his bandage that has been caught inside Lovecraft's body and urges Chūya to finish him off.

Aftermath
With Lovecraft defeated, Chūya goes on an uncontrollable rampage, until Dazai holds his forearm and nullifies Corruption. Chūya also instructs Dazai to bring him back to his base before he passes out. A curious Steinbeck asks who they are for having defeated someone like Lovecraft, to which Dazai vaguely responds that they are merely enemies of bad guys.

Moreover, Dazai leaves Chūya behind and heads back on his own despite promising to bring him back to the extraction point.

Manga and Anime Differences
The anime includes Chūya defending himself from Lovecraft's tentacles with a force field-like gravitational sphere before launching his projectiles. It also adds Lovecraft impaling Chūya with various tentacles before getting repelled by Chūya's repulsive gravitational force. A subtle difference also shows Chūya emerging from behind Dazai in kicking Steinbeck in the manga, while the anime portrays him kicking right in front of Steinbeck.