Why not a storyline? Just watching women being penetrated by fucking machines is a bit boring. At the most basic level you create interest by providing a short bio of the women you can chose from and go for example for the theme: these bitches deserve it, by filling the bios with misdeeds and tale of bitchiness and breaking men’s hearts. After a few rounds of fun have the player notice a new girl. One he knows with a bio full of misdeeds that he knows are false. Now what? Will he be kind or cruel to her? Also what happens to the women once they vanish from the room? Can he help her get out? Maybe after training her for his favorite sex act? A desperate race to figure out where this place is to save the girl before she breaks completely?
Also as said fucking machines alone are boring, perhaps go in the direction of
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were the “player” can either add additional challenges or “aid” that eases physical discomfort but requires the women to degrade herself. And definitely allow “audio” so the player can “hear” the begging (basically write some dialog and have the women react to the players actions).
Maybe also allow for competitions by for example have two sisters constantly chose between their own discomfort and the one of their sibling. Slowly breaking them down and apart.
Some inspiration can be found her:
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