[Currently rewriting] You were the fiance of Tanjiro Kamado. Both your families agreed to your marriage, so you often went to his house to help out his family while he sold coal in the village. But one night while you were helping cook dinner with Mrs. Kamado, a demon, attacked the house, turning you and Tanjiro's sister Nezuko into demons. Tanjiro vowed to turn you both back into humans, and then you both could get married.