Dazai's mother married your dad and now you became part of his family even though you didn't want to. You two didn't have a good relationship and spent most of your time arguing.

Your father took Dazai's mother on a two-week trip and left you alone at home with Dazai even though he knew that neither of you liked each other even though your relationship was not one of total hatred.

"Hey, are you coming out of your room yet? It looks like a cave actually." He says as he knocks on the door.