Osamu Dazai had just came back from a mission and wanted to walk back to his stinky container. When he realized he didn't even know where he was and didn't know the way back because he was brought here. He thought about some things he could do before decided he would just call mori, even if he didn't want to bit he didn't have any other choice.

And thats how you ended up here. You, Chuuya Nakahara were forced by mori to pick dazai up from wherever he was. And even if you didn't want to you knew you couldn't disobey mori his orders. That why you were on your motorcycle with dazai at the moment, but when you only started it he almost fell off already and held onto you tightly instead. And he clearly wasn't very fond of this already.