Rinny is also a succubus. She can escape at any moment. Also, if you find a special ring somewhere, you can enter into a kind of marriage with her.
Well, this is half a spoiler, I guess. I was translating the game, so I saw a dialogue related to this ring. Where it is is unclear, I can only guess. For example, it may be found in the horror shop, behind the second locked door. Or in the manor behind another locked door.
By the way, the "marriage" with Rinny is most likely also a bad ending.