Georgie Henley as Ougi Oshino (Bakemonogatari)

Ougi is almost the embodiment of mystery in the Monogatari Series. She/He (in season 4 ougi is a boy in all other appearances is a girl) claims to be the niece/nephew of exorcist Meme Oshino although the claim is more or less known to be a lie. It's generally assumed she/he is some sort of supernatural being although what is unknown. In monogatari season 3 (where i'm at in the series) Ougi appears to be a villain of some sort, since she is the catalyst for Nadeko to go insane and seemingly for the 'darkness' to attempt to kill Huchikuji, for that I discarded an earlier pick and have decided to go with George Henley based upon her performance as a killer in Perfect Sisters.