Ohtori Kanae

On the surface she seems to be kind but vapid, but it is possible that she knows something of the academy's inner workings. She insinuates that she knows Akio isn't engaged to her for her, but for the power he can have because of it. Later in the series she loses her own willpower and becomes very much a puppet of Akio's. She was most likely made this way because she somehow interfering (intentionally or not) with Akio's plans. In other words, she was the girl who knew too much.