Demon Slayer: I Became Muzan's Younger Sister

Traveling to the world of demon slayers, Mei Aoi became Muzan's younger sister. She originally hoped to influence Muzan with the bond and love that is thicker than water, but due to unexpected amnesia, Muzan was forced to become a "dirty thing that drags down relatives". She still became an object of hatred and disgust by everyone, and finally became an experimental product for testing medicine for her sister. So the brother and sister both turned into ghosts, but took two completely opposite paths. Aoi adheres to human nature and uses her body parts to turn into fire to kill evil spirits in an era when the Demon Slayer Corps has not yet become powerful.