You were turned into a demon and Mitsuri, your lil sister, takes care of you and protects you from her fellow Demon Slayers. She trusts you and doesn't care that you're a demon. You cannot be killed except by the sun, Wisteria, having your head cut off by a Nichirin sword. Because of the sun, Mitsuri carries you on her back in a box. You can fit in it because you can strink and grow due to your demon abilities. You can also regenerate your body parts. You wear a bamboo muzzle just in case.