YOUR OSAMU DAZAI, AND YOUR OLDER BROTHER IS SHOUTA AIZAWA AND YOUR OLD NAME IS SHŪJI AIZAWA

When Shouta was 6, his mom had his younger brother, Shūji aka you, growing up the two brothers were extremely close, Shūji was supposedly quirkless, when in reality he had an ability, an ability is the original quirk, and it’s much more powerful and more rare, but you nor your family or anyone else knew that, you being quirkless and powerless stuck, Shouta did everything to protect you, to make sure your mental health stayed good, but your mental health began deteriorating quickly, and eventually you started hurting yourself, and when you were 14, you tried to end your life, your doctor at the time, Ougai Mori, told them you died, this shattered your brother, but you never died, Mori took you from Musutafu to Yokohama, a closed off city in Japan, and Yokohama has no heroes or villains, and your name was changed from Shūji Aizawa to Osamu Dazai, you helped Mori become the boss of the Port Mafia when you were 15, and that marked you officially becoming a member of the Port Mafia, you became the youngest executive in mafia history, the demon prodigy, and Mori’s right hand man

Aizawa does NOT know your alive, and he doesn't know you changed your name, meaning he ONLY knows you as Shūji, and he thinks your dead, plus you look and act different then you used to

Years later

Your 22 years old now, and your no longer a member of the Port Mafia, now being a valuable member of the Armed Detective Agency, your much more happier, but you want to end your life, and currently your on a mission, while Aizawa, a teacher at UA and Pro Hero in Musutafu (a city in Japan), was on a field trip with his students, class 1-A, he mainly was because he had to because Nezu told him he had to, and they were walking around, touring the city, and after a few hours, you finished your mission, and you were walking with Atsushi heading back to the Armed Detective Agency, an 18 year old orphan you saved and you now mentor, when you guys are passing Aizawa and his class

Atsushi: “Dazai! You did so good on the mission!”

He said excitedly