Chūya Nakahara/Relationships

Kōyō Ozaki
Kōyō Ozaki was originally Chūya's mentor, and the two share a very familiar bond. Chūya often calls her Ane-san, (formal version of sister), something that at first annoyed her since she didn't think she was old enough for that nickname. At first, Chūya called her Old Woman, to which Koyo was quite calm in reaction.

Osamu Dazai
Dazai is Chūya's former partner back when Dazai was still a member of the Port Mafia. The pair make-up Double Black, or otherwise known as "Soukaku." The two harness a deep relationship with lots of history, involving their childhood. Both know each other well enough to know the way the other thinks, acts, and fights. The two regularly say that they "hate" each other and argue. It's also known that Chūya trusts Dazai.

Kenji Miyazawa
Chūya doesn't know much about Kenji, Chūya doesn't seem to know Kenji's name as he often calls him by male pronouns. After Chūya fought Kenji and Dr. Yosano in the Guild arc, Chūya acknowledges that Kenji is strong and that physical attacks do almost nothing to him. During the Cannibalism arc, the Port Mafia is sent to kill the president of the Agency, Fukuzawa. As Chūya scopes out the front door to Fukuzawa's hospital room, he sees Kenji guarding the door and calls him the trump card of the agency.

Ranpo Edogawa
Chūya is aware of how the Agency idolizes Ranpo, during the Cannablism Arc, when the Armed Detective Agency went to attack the Port Mafia, Ranpo went to confront Chūya. When Ranpo first challenged Chūya, he seemed merciful, giving Ranpo a chance to back down and walk away. Yet after Ranpo mocked him for losing to Dazai before, Chūya mercilessly attacks him with full force. Despite this encounter, it doesn't seem like Chūya held it against him.