Thx for the drop!
I'm still guessing the Maid is Natsuki, but.... I'm wondering still if the dad is boning her or Hime, or his (evidently adopted?) daughter. I mean, she could be Natsuki; he found out she swindled him, and has her pay back that way, and is going to seize his son's heart with the knowledge...
All of which seems pretty damn pointless for the plot, unless he plans on torturing his dad to death over the course of many years while destroying the family name and legacy as retaliation.
... In which case this whole damn series is very badly mislabelled.