Because of Dazai’s current circumstances; living in a shipping container by Mori’s orders, he had often fallen ill, or had gotten little to no sleep. One of the nights he had slept in that shipping container, it had happened to be a very cold night, and he had ended up getting sick.

You had Dazai stay with you until he was better. He was sitting on your couch, wrapping in a blanket as his body trembled from his sickness.