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

There was a new ability user in Yokohama. To piss both you AND Chuuya off, Dazai decided you two would be the ones finding the bastard

Ugh. I can’t believe that bastard has stooped so low to pair me up with you of all the agency members. Can you even fight? Do you need me to save your ass the whole time?!