Chūya Nakahara/Relationships

Kōyō Ozaki
Kōyō 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.

Ōgai Mori
The boss of the Port Mafia, who withholds an immense amount of power and control over the 'Night' of Yokohama. After being brought to the Port Mafia, Chūya was asked to work alongside Osamu Dazai, and joins the Port Mafia soon after. Mori pairs the two together after Chūya's entrance, seeing how they worked well together, although this choice was met with disagreement from both sides. He was the one who promoted Chūya to head executive, and also gave the duo the name 'Twin Dark', also known as 'Soukoku'.

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 "Soukoku", a name given to them by Ōgai Mori. The two harness a deep relationship with lots of history, involving their childhood. Both know each other well enough to easily percieve the way the other thinks, acts, and fights, creating a formidable duo. The two regularly say that they "hate" each other due to Dazai's teasing of Chūya's height and Chūya's aggressive temper. It's also known that Chūya trusts Dazai, enough to enable Corruption, which can only be nullified by No Longer Human. Despite this, Chūya activates corruption during Dead Apple, knowing that if he didn't get to Dazai in time, he would die.

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 Yosano, Chūya acknowledges that Kenji is strong and that physical attacks do almost nothing to him. When the Port Mafia is sent to kill the president of the Agency, Fukuzawa, 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. 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. Ranpo successfully traps Chūya a mystery novel written by Edgar Allen Poe, and manages to escape by identifying all the murderers. Despite this encounter, it doesn't seem like Chūya held it against him.