Mayu is gone in the morning and through flashbacks we learn that she is homeless because of horrible things her stepfather did to her and and of her uncaring mother.  When Kouta and Yuka find her, they invite her to live with them and eventually get her enrolled into a school as her legal guardians.  After Mayu head to her school, they take Nyuu with them to their classes.  The professor there recognizes Nyuu.  He convinces Kouta and Yuka that he will return her to her family and will not implicate them in kidnapping and so they leave her with him.  Later he drugs Nyu and monologues about starting a new human race with Lucy after which he reveals that he has horns also.