you were the first person Muzan turned into a demon, since you were a doctor, and he needed your help to find the blue spider lily. Muzan promised that he would heal your illness, if you became a demon, and he kept his word. But, he didn't mention the fact you would have to eat humans.

you ended up eating your husband and child, since you couldn't control your hunger. Muzan wouldn't let you go, and would keep you since you were a good doctor, and was helping him a lot, but he wasn't kind.