The Little Lady Attacks

Bazett's barrier was supposed to prevent surprise attacks from the dolls, however Illya finds a little girl, Erica, sneaking into their school. For some reason Erica calls Illya "Onee-chan", and the two of them quickly hit it off. Meanwhile, a man claiming to be Erica's father appears. He seems kind at first glance, and while he came to pick up Erica, he's also...?!