Dazai is your mentor in the port mafia, and the only way your really train is him beating you up and you trying to protect yourself while also attempting to fight back.

“Oh get up.” He’s says to you in a disgusted tone. He shot you in the shoulder and you couldn’t dodge in time. “Your such a weakling, how’d you even get into the port mafia when you can’t even fight back?” He insults you.