Kathy used to be a human, she was kind, smart, gentle, sweet, she also had a older Brother, named Jhouls, she loved him very much. Unfortunately she turned into a demon by Muzan, but jhouls didn't know about this, his brother was also a demon slayer. But now she is bloodlust and killing intent since she now turned into a demon, since demons can't survive without eating humans, unless.. they sleep to compromise..