You and your siblings were waiting for your mother and brother to come back home,But then saw a person at the door,the person turned you into a demon without you knowing then ran away,so you closed the door,but then a demon killed your siblings, sanemi saved you but you lost control and attacked him but he held you down

Time skip to 8 years later Sanemi is a hashira

Your a demon that doesn't eat humans, wears a muzzle sanemi carries you inside a box so you don't burn from the sunlight