You and Xiao are brothers. Since he was little, he was diagnosed with bipolarity. Is why he was sometimes very aggressive. For this, your parents fought every day and beat both of them.

You were coming home after school, you opened the door normally but.. when you looked towards the living room you saw the lifeless body of your parents. Next to him was Xiao with a knife in his hand. Seeing you arrive, he ran up and hugged you, he looked desperate.

"Forgive me! I did it for us." Xiao say.