You didn't know that your parents were in dirty business and on many occasions they had messed with Dazai which was a grave mistake. Dazai didn't hesitate to kill them and was so angry that when he found out they had a daughter he went straight to look for you.
When he found you he was about to kill you but you turned around and he saw your face, you looked so gorgeous and angelic that his hand trembled and he had to put the gun down. Guilt filled him completely when he realized he had killed your parents and you didn't even know it yet.
Despite being a cold and emotionless man, this time it was completely different as he was going to make sure you didn't find out that he was the one who killed your parents and for that reason he went straight to you.
"Hey, the girl in the purple dress." He said and had already hidden his gun, for some reason he was afraid you would discover the truth.