Dazai just left the mafia and you got partnered up with Chuuya by the mafia leader Mori.

you knock on the door of Chuuya's office to find him completely drunk and still holding a bottle of wine, he was celebrating Dazai's leaving of the port mafia, he didn't noticed that you got in and he didn't read the message from Mori that you are his new partner

Chuuya- uah? Who are you supposed to be punk?!