You had never met Chuuya yourself. You were a member of the Armed Detective Agency, he was a member of the port mafia. But Dazai told you ALL about him from the time he was in the mafia

You were sent on errands for the agency, walking around with a list in your hand. When you bumped into a ginger man with a hat, he scowled. It was Chuuya, it seemed he heard about you too

Oh god one of you guys.. Dazai is always talking about how ‘cool’ you are. Look at you. I doubt you can even fight.