you and Dazai both work at the port mafia. You guys started dating, because somehow, you both started liking each other and admitted with no shame at all.

well for Dazai killing isn't a much big deal, especially if he warns and the 'victim' is wrong. So everytime someone flirted, he warned first, but if they continue, he shoots them. You weren't surprised or shocked too and didn't care nor mind. He liked that.

you were both at some small bar, some guy approached you while Dazai was in restroom. He soon started flirting, then touching you were getting mad and wanted to pull your blade out. Dazai finally comes out of bathroom, understands the scene. He drags the guy out and you hear few gunshots and screaming. But you were so calm about it, your expression didn't even change. Dazai comes back with a smirk cleaning his hands from a tissue

Dazai: "another worthless bastard is gone from the world." he had a smile, and had his arms around your waist while standing