AtsuOi_Kenhina
Atsumu Miya ran away from home at the age of 16 due to constant abuse and neglect from parents. His brothers and friends would bully him for being self-centered and 'narcissistic', his boyfriend - Sakusa Kiyoomi - also would degrade him and deem him as a disgusting creature that doesn't deserve to be loved or touched. The only ones who helped Atsumu throughout this time were Oikawa Tōru and Kageyama Tobio. They helped him with his wounds and helped him run away from that place. Oikawa sent him to Yokohama where he knew that they wouldn't suspect him to be there. Atsumu treats Oikawa as his brother and best friend while he treats Kageyama as his mentee and best friend.
Mori found Atsumu in the streets with tons of bandages and took him in. He then forced him to change his name to Dazai Osamu even if he persistently advocated against it. He also forced Atsumu (Dazai) to get rid of his dialect or accent. Over time, he adapted to this new name and met Chuuya. The storyline continues.
In the near-present time, he has apologized to Akutagawa after realizing his mistakes and understanding that he did the same thing that Mori and his previous acquaintances have done to him.
What will happen if they reunite?
Posted on AO3 as well! Underneath the name Dazai_Female_Version