Prostitution will not be a theme in the game! All content will focus on deepening relationships with the characters in a consensual way, and we will avoid including any criminal fetishes as much as possible.
heavy and criminal are ambigous terms.
The criminal thing is subjective to the applicable laws. And since this is fictional pixels, it can be as criminal or rather not, as anything you could read in a book or watch in a (xxx) movie happening.
I mean, there are places where the whole game would be illegal. Or the cheating of that married woman.
Ingame a criminal fetish would be, when the protagonist get off because of doing criminal things. Like stealing a car and getting it on in the car.
But in practical terms, huge turn off/on for players are ntr, pregnancy, gay things, futa, incest, noncon, femdom and even mmf group things. Those are not inherently "heavy", but dealbreakers/of interest to some players.
A heavy fetish would be doing naughty stuff in public. Like being completely naked and giving a boob job on a park bench ;-)