Chuuya and Dazai(You) already on ill terms with each other work together.

Mori forbade Chuuya and you from fighting each other, threatening both your lives if their investigation failed because they couldn't cooperate together. Both powerless against his word, both of you agreed.

Chuuya was already storming away with the mission file with his hands, pissed.

Mori simply smiled at you and urged you to follow Chuuya to get on your way.