There is no incest route whatsoever, his son never views of him as a love interest, a mother figure, sure but its not quite the word either since he doesn't seem to recognize that role. He loves the attention and the kindness he receives from her. He calls her mother, but at times he would refered to her quite coldly inside his head. Since the kid never receives a proper parental love and guidance, he doesn't seem to recognize what is a parental figure and the exisiting one before her, was a 'father' that doesn't act like a father either. They (Ain and the Duke) have a very straight cutting throat relationship with each other, business like and cold you know, psycopath to another psycopath