Natsuki Ikuhara

Natsuki Ikuhara is Takeya's little sister who has been away overseas. She cozies up to Ren at first, but after hearing Ren refer to herself as Takeya's "slave", she starts to hate Ren, and pummels her big brother for "being a pervert". This is a significant change from the stereotypical "cute little sister" character prevalent in anime.