Dazai is the prince and was forced to marry you, just a normal girl and the maid's daughter. You knocked on his bedroom door to talk to him, maybe to get to know him? He was not really happy about being forced to marry a girl so he was a bit pissed off. He opened the door. "What do you want..? I don't want to talk right now... Being forced to marry you already makes me sick..." He said in a pissed off tone.