Chūya Nakahara/Relationships

Paul Verlaine
Paul Verlaine and Chūya share a very complex relationship. Paul Verlaine first met Chūya when Chūya was sixteen. He told Chūya that he is his older brother, before asking him to leave the Port mafia to come with him. In a effort to convince Chūya to do this, the professional assassin begins to methodically kill anyone Chūya has a reason to stay in the Port Mafia or Yokohama for. This makes Chūya, Dazai, the special abilities personnel and robot Adam Frankenstein, and the mafia, target Paul.

After several deaths, Verlaine finally goes after his final target, the mafia head Ōgai Mori. This culminates in a battle against the entirety of the Port Mafia, ultimately ending in a large portion of the mafia dead and Verlaine subdued. Verlaine now is a Port Mafia executive alongside Chūya and Kōyō. He works as as a trainer, to teach assassins in the Port Mafia. Currently, his known pupils are Gin Akutagawa and Kyōka Izumi.

Kōyō Ozaki
Kōyō was originally assigned as Chūya's overseer, and the two share a very familiar bond. Chūya refers to her as Ane-san, (the formal version of sister), something that at first annoyed her since she didn't think she was old enough for that nickname. However, she now seems rather accepting of it.

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'.

Ryunosuke Akutagawa
Throughout the anime we don't see Akutagawa and Chuuya interacting much with each other. From the small glimpses shown during Dead apple it is clear that Chuuya doesn't treat Akutagawa like a subordinate, instead he trusts him enough to ask him to lend a shoulder to him during the Dead apple conflict. Chuuya has shown concern and care towards Akutagawa in the drama CD where the Port Mafia goes to an Onsen for a relaxing time. Chuuya acts as a caring and wise mentor towards Akutagawa and sometimes even gives him advice about the former's complicated relationship with Dazai.

The Flags
The flags were Chūya's first friends in the Port Mafia, a young mens association of the most promising in the Port Mafia under 25. They all seemed to care deeply for Chūya and went out of their way to locate information about his past to comfort him. Unfortunately on the one year anniversery of Chūya joining the Port Mafia they were all slaughtered by Paul Verlaine.

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.

The two took an instant disliking to each other the moment they met, and Dazai was responsible for extorting Chuuya into joining the mafia by manipulating the Sheep into believing Chuuya to be a traitor and threatening to kill the gang should he refuse to join. Later, as adults Dazai gets himself captured by the Port Mafia in order to both help Atsushi and utterly humiliate Chuuya by forcing him to betray the mafia, whom he considers his family. The two also celebrated Dazai quitting the mafia, with Chuuya opening up a bottle of exceedingly expensive wine and Dazai bombing his ex-partner's car. It's also shown they do not interact much unless forced to, though they are able to carry out missions without their mutual hatred getting in the way of their success.

In Storm Bringer, during Guivre the Beast's assault on Yokohama, Dazai is only motivated to fight when Mori points out he would technically be committing double suicide with his partner should he die. However, while explaining Corruption is their best bet for winning to Chuuya, he adds on the fact that the logs containing the answers Chuuya had been seeking his entire life would be erased and gives the other boy the genuine choice to use it or not without manipulation, in a rare act of kindness towards his partner. When Chuuya decides to use Corruption and passes out in the sky after defeating the monster, Dazai is also there to catch him.

Akiko Yosano
When meeting her for the first time, Chuuya gets excited to fight someone while Yosano only demonstrates her typical sadism for her opponents. Despite being enemies, Chuuya does not seem to dislike Yosano or hold anything against her.

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.

Buichirou Shirase
Shirase was the first person to help Chūya in the Sheep, offering Chūya his bread when he was starving. The two of them were friends in the Sheep, but as with the rest of the members, Shirase relied to heavily on Chuuya's ability and took advantage of him. During the fifteen arc, Shirase and several other members of the Sheep met Chuuya and Dazai in an arcade, where Dazai planted distrust of Chūya in their minds. Because of this, Shirase and the other Sheep chose to betray Chūya by stabbing him and joining forces with the GSS. Despite this Chūya ended up joining the Port Mafia and cutting a deal with the Port Mafia to save his and the rest of the Sheep's lives.

A year later, Shirase was still being used as a hostage to keep Chūya in the mafia. When Shirase was under threat from Verlaine, Chūya went out of his way to protect him. Shirase ended up accompanying Chūya and Adam on their mission to stop Verlaine. During this time, Shirase learned of his mistake and what Chūya did to protect him. He also realized that Chūya was a child like him and risked his life to protect him. By the end of Stormbringer the two of them said goodbye to each other as friends when Shirase left to start his own organization in London.