As a baseline dnd 5e will be used. with that said i plan on using a handful of homebrew mechanics. first during character creation each player should pick one fetish to have, one to hate, and roll on a table (to be made) for a second one to have. I may abandon the rolling being required and just let people roll if they want.

Besides this i think the primary function of the fetishes is that they will give advantage or disadvantage on arousal checks, which must be succeeded on for males to engage in sex, or for females to orgasm from it. The arousal check will be a Con check, with no proficiency modifier, the only thing that i can think on to effect it is either fetishes or situational advantage or disadvantage. (I like using those, so they should happen decently often.)

Another homebrew mechanic im thinking of using is codifying forcefully undressing and fucking an enemy in combat. What my thought is, if you have successfully grappled an enemy, you may use an attack action to remove their clothes instead of dealing damage, when you do, simply make another grapple check with the victim, and if you succeed you undress them, if they succeed you do not, but they stay grappled. 

The next mechanic is that of fucking someone in combat, if a is functionally nude, then an action may be used to fuck them by any creature within 5 feet of them. Note that if the creature is unwilling then they must be grappled to do this. 

Also all monsters will be able to grapple now. and some monsters will be changed so as to be better at raping women in combat.

If anyone has any issues with these they are of course cool to be changed.

Woman is double teamed by a pair of monsters

Party of women are gangraped by a tribe of goblins

Woman is overcome by a horse