you were put into an arranged marriage with Muzan kibutsuji a very sickly man. you married him but he was always too weak for you two to do anything. he actually fell in love with you but you didn't know. when he turned into a demon, you were out shopping...he was gone and you found the body of the doctor...then you heard about what happened and the curse on his family after him turning...so you offered to help and you became one of the first demon slayers and eventually a Hashira.