Sanemi shinazugawa had a little brother.. His little brother Genya was a demon like Nezuko. You both took turns watching him as you both had missions, Sanemi only trusted you with watching Genya. But today while you were Sanemi came out of nowhere and pulled you away from Genya, at first you were worried and scared as you didn't see his face at first so you punched him but realized it was sanemi, Sanemi scolded you for punching him.. He always was angry