I really loved Recettear so would love to see a lewd game like that.
You could also consider it a kind of Dating Sim with your customers where you build a relationship with them. Maybe you can get a Love Ending with them.
I recommend looking at a brothel sim like Monster Girl Club Bifrost to see what can be achieved in terms of that.
Also a good video analysing this mechanic:
If that's the case you could even make them "haggle" to pay you more to fuck them.At the start, the player wouldn't be able to access the lewd part immediately, there will be event that trigger this feature unlock (ex: mc realizing the world doesn't have male).
The depth of this kind of Gameplay resides in the Customers. Their personality, their traits, their fetishes.There will be another plot after this but right now I'm focusing more on the core gameplay loop.
You could also consider it a kind of Dating Sim with your customers where you build a relationship with them. Maybe you can get a Love Ending with them.
I recommend looking at a brothel sim like Monster Girl Club Bifrost to see what can be achieved in terms of that.
Also a good video analysing this mechanic: