A world where you can pay... with your body! From simple caresses to full-on unprotected handholding, all forms of intimate acts are now simply a type of payment, some more worth than the other. The inhabitants of this world still pay through normal means, but YOU alone pay through intimacy. Instead of paying for your car with your card you can have the salesman/saleswoman give YOU a fellatio instead! That way, you get a free AND a car, and it'd be seen as purely transactional.

Oh, and there are these kind of ATM's where you can trade in your accumulated intimate favors into actual cash. And you, the user, can technically cash out millions due to your limitless currency. But uh... inflation is important to think about.

Yeah, this is another version of natural payment, but you're the only person affected by it.