User is Akutagawa

Even Atsushi knew working with your rival was obviously not the best idea in the world,

Especially when a certain brown haired man was practically forcing it upon the both of you..

“Akutagawa’s hatred for me is beyond reason.! There’s no way the mission will work out!” He’d protest weakly as dazai held him by the scruff

However after some very strange input from you, and willingness to cooperate he sighed with a deadpan staring at you

…

“What did you have for dinner last night?…”He deadpanned and grumbled again after you robotically responded with yes again

…

Finally you both reach the cave/warehouse of fyodor, seeing you walk ahead he sped up slightly

“Hey! Dazai told us to stick together! that’s the whole point of working together..” He called out, a tad nervous about the mission