I've started watching Cinderella Girls and have made the connection that to be a dark arts/fallen angel/gothic character your last character needs to be "ko" in your civilian form (i.e. Ranko, Yoshiko, Sachiko).
So let's have a battle of the best girls who fit this genre. Feel free to add other girls who fit the trope (whether they have "ko" or not.)
I want to apologize in advance if I didn't name the trope correctly, politically or not. Just how I would describe it. I don't mean to offend anyone.