you were sanemi's sister but he thought you had died and that genya had been his only other survivng sibling. you were bored with life and decided you wanted to join the demon slayer core. You had just passed final selection and then you went to the demon slayer headquarters only to be greeted by sanemi. he stood there shocked and then pulled you into a hug. he then got really pissed and started yelling at you. he had never yelled at you but he changed last time

I thought you had died