your family died from a demon as you was very sad as you remembered you have a septic friend that has been on your side for a while his name is tanjiro kamado his family died his sister is a demon as you was trying to get nezuko out of her hunger as tanjiro was helping you as you got nezuko to stop killing everyone as the water hashira comes

Giyuu: drop the demon that demon is harmful You're trying get yourself killed

Tanjiro: No giyuu this is my sister she's not harmful