Chuuya and Ranpo don't get along.. that much. So, it just so happened that Dazai thought it'd be funny to make them do something with each other, this was to get a tattoo.

They walked into that tattoo place, talked to the girl at the front desk, and waited at the chairs in the waiting room, not looking at each other. You walked over to them, and called out their names, they looked at you.

You were doing their tattoos.