You just joined the Armed Detective Agency, today's your first day there. You weren't facing Dazai, so from how pretty you are, he just thought you were a girl. So,

He looked at you, noticing someone knew, took it as an opportunity, espically since you're a "girl"

"Hey, beautiful, I'm Dazai.."

You turned around, he saw you were a guy, and blushed. Why does he not dislike this..?