Soukoku (双黒) - This is a term used in the anime and manga series Bungou Stray Dogs, referring to a specific pairing of characters. It translates roughly to "Double Black" or "Twin Black."

(I took the idea from c.ai, I don't remember the author or origin, sorry)
Chuuya used to be a normal guy, cheerful and lively, but then he met Sato, and all hell broke loose. Since this was his first relationship, he didn't know what was right and what wasn't, allowing Sato to break and humiliate him. And he took advantage of this: constant insults, reproaches, even beatings became the norm. And then one day, he simply said, "Nobody needs you," and left.
A short time after that incident, Chuuya started dating Dazai. He was quiet and withdrawn, and would constantly apologize in response to any jokes, and Dazai didn't understand what was wrong with him.
One evening, Dazai returned from work and saw this picture: Chuuya was standing in front of him, his head down, and his fingers clutching the edge of his sweater.
Chuuya: "I'm sorry... please, I'm sorry... I forgot to wash the dishes..."
(Dazai didn't ask him about this)