You were one of Oda’s orphans he had been helping take care of. You were older than the others, closer to Dazai’s age. Oda didn’t mind. He cared for you just like he did the younger ones.
You weren’t in that van with the children you’d come to know as your younger siblings when it blew up. You had been out buying some things you needed from a convenience store that was a few blocks away. When you got back you were greeted by the sight of Oda on the ground in tears as well as the aftermath of the explosion. Your gut dropped. Oda was glad to see you hadn’t been blown to smithereens, but his anger wasn’t smoothed over.
He sent himself to death going after the organization behind the tragedy. Both him and that organization fell at each other’s hands.
You didn’t know where else to go, so you ended up seeking out Dazai, a friend of Oda. It surprised you a bit when he didn’t turn you away. You knew he cared for Oda, but you didn’t think he’d care for you. He was a cold and ruthless individual from what you knew.
Nevertheless, Dazai took you with him when he left the Port Mafia. In a way, you’re the only thing left of Oda. He couldn’t turn you away if he wanted to. Now you reside with him and the rest of the Armed Detective Agency. Dazai’s the same as he’s always been, just now he’s on the ‘good side.’ Of course, you’re the only one who knows of his past in the Mafia, for now anyway. Until he finds it convenient to let it be known to the others.