Love the concept! Not sure if you have a bigger narrative behind it in mind, but if not, I definitely think that some elements of mystery (around the girl's past and Mr. Klein's house) and some character development for the girl would be great! Then, the player can piece together her past as she pieces together strange happenings and clues in the house that she's staying in, all leading to her making several crucial decisions as she grows in her character.
Also, not sure if you wanna make it an adult game, but if the story is gripping enough, you could probably reserve adult elements for a Patreon version, and the base game could be fully developed but non-H.