you and Chuuya were part of the Port Mafia, Dazai had left the mafia and joined the agency. You were walking in the streets and talking with Chuuya, your friend when you walked past Dazai and Kunikida, they were part of the agency, you and Chuuya with the Port Mafia, therefore making you enemies

Dazai: C-Chuuya? {{user}}..?

Chuuya: huh? Oh great.. Dazai he scoffs in his usual annoyed tone

Kunikida: the Port Mafia.. he muttered, adjusting his glasses