Soukoku

Soukoku is the slash ship between Nakahara Chuuya and Dazai Osamu from the Bungou Stray Dogs fandom.

Canon
Both Dazai and Chuuya were paired up with each other when they were 15 years old. The man who had paired them was Mori Ougai, the new chef of the mafia, who reasoned that "only diamonds can be polished by diamonds."

The duo was named Soukoku after one memorable night during the events of "Dragon's Head Rush", where they had defeated an enemy organization over night. This resulted in them recognizing themselves as Soukoku, or Double Black, among other enemy organizations. They are also known as "Yokohama's vicious duo". The pair also have unconditional trust with each other. As stated in Bungou Stray Dogs: Dead Apple guide book, "The core characterization of Dazai and Chuuya's partnership is based on pure trust where both of them are capable of leaving each other's life on the other's hand without a second thought or doubt." (pg 54-55).

Their partnership collapsed for four years when Dazai decided to leave Port Mafia and join the Armed Detective Agency. However, their partnership, resumes during the conflict with the foreign organization The Guild. Also, the duo seem to be know each other to a questionable point when Dazai says he knows Chuuya's "Thrust", to which, Chuuya responds with "I was just going easy on you".

That being said, Dazai once desired to witness the nudity of Chuuya in Bungou Stray Dogs Wan!. The duo also competes against one another as evidenced by when they are found in a competition against each other for who can eat the most ramen. Adding onto it, in Chapter 20, Dazai even dressed up as a dog to catch Chuuya's attention, despite his dislike for dogs. Following the event, he once dressed up as an old lady who could not walk properly, and made Chuuya carry him to the other side of the rode. Dazai also has a record for climbing up to Chuuya's office just to give him a cup of coffee, simply reasoning it as "My partner worked hard so I came to give him a cup of coffee."

In Dead Apple Chuuya uses corruption to save Dazai, even if Ango says him that he's dead for sure. Chuuya trust Dazai's inability to die and he know that it's a plan that involve him saving Dazai. Then Dazai disactivate corruption chering his cheek, the duo falls in a romantic music while Dazai compare himself to Snow White, asking Chuuya for a softer way to wake him up (Chuuya punched him).

When the duo falls on the ground Dazai forces Chuuya to rest on his lap, because he doesn't want to save him if the fog separates Chuuya from his ability.

Fanon
It is believed that Soukoku is a business ship since it earns and buys a lot, however, many disagrees as well. It is also believed that, their name of the partnership was supposed to be "Double Shades of Black" but was changed to Double Black.

Trivia

 * During the character designs, the creators of the series mentioned that Dazai and Chuuya would be in a Partner/relationship, as well as that Chuuya was originally designed for Dazai.
 * The ship is the most popular ship among the Japanese and Western fandom.
 * Their stage actors ships them (Dazai played by Hideya Tawada and Chuuya played by Ueda Keisuke).
 * The sentence used to introduce the Double Black episode was "The head may err, but never the blood." (Showing the depth of their relationship as something magnetic and rather deep.)
 * Dazai is 51 days younger than Chuuya.
 * They express their emotions toward one another as "I hate you". However, they also get very worried when the other is hurt, as well as very proud when the other accomplishes something. (episode 9, season 2)
 * There seems to be some sexual tension between them (Chuuya once pulled Dazai Osamu by his hair in episode 10 from season 1).
 * Their height difference is 21 cm (Chuuya - 160 cm, Dazai - 181 cm).
 * They have a whole episode dedicated to them for their reunion in season two, called "Double Black".
 * Chuuya has put his life on the line just to save Dazai many times.
 * Dazai, despite his hatred for Chuuya's hat and clothing, still folds them and wipes his blood off his face in episode 21 from season 2
 * During one of the twitter events, Chuuya confesses that he is, indeed, in an inseparable relationship with Dazai. 23621625 1736650933306568 8488735499124480906 n.jpg
 * Dazai once stated that he did not enjoy the company of men or hugging men. Yet, in one promo picture, he is seen hugging Chuuya from the side, while wearing a very amused smile and winking at the other man.
 * Red camellias (Camellia Japonica) are often used to represent them. The said flower stands for love, passion, trust, and desire. In some cases, it also represents death or sorrow of losing someone, and is related to Chuuya's ability (For the Tainted Sorrow), where he has a higher chance of dying.
 * Dazai, similarly to Mori Ougai, had also paired Nakajima Atsushi and Ryunosuke Akutagawa as "New Double Black" or "Shin Soukoku", where Shin Soukoku reflects more if not less of Soukoku.
 * The name was canonically given to the pair of men from the boss of mafia, Mori Ougai.