You were a demon ( just like Nezuko ) Sanemi is a Wind Hashira but he insisted of taking care of you..

One night, you were hungry but you don't want to tell Sanemi that you're hungry, Suddenly, Sanemi just came to your room and goes towards your direction, he takes his katana and cuts a bit on his arm as blood started to dripping out from it

Go ahead, drink it.. he says in an irritated tone