For some reason, I've been thinking of ways to turn existing games into hentai games. I probably wouldn't make any of these ideas on my own, but I might lend support if you want to take on one of these projects yourself, and I won't get mad if you "steal" any of my ideas.
Feel free to suggest your own ideas too.
Infectonator
First up, I've mostly played Infectonator: World Dom so pardon if I missed something from one of the other variations of this game. In this game, you play as a mad scientist infecting the world with your zombie virus (or maybe you play as the virus itself, not really sure). In the original game, there are a bunch of people wandering around, you tap a group of them with the mouse, they turn into zombies and start killing people, possibly turning the killed people into zombies. The obvious hentai-fication would be to turn people sex-crazed so that they go after other people in town and fuck their brains out instead of eat them. The original game has people like soldiers and cops shoot at your zombies, which seems a little over the top for sex crazed. Maybe cops or nuns could just try to stop your sex-slaves with tasers or holy charms or buckets of water or something. Or this could be set in a medieval fantasy setting, and pure wizards could cast spells to undo sex-slave-ism. Or wizards could just exist in an urban setting. Final Fantasy Infectonator Hentai, why the heck not?
I feel like decent graphics would be very work intensive. It might help to limit the game to side-scrolling view, like Golden Axe or River City Ransom, so that you only have to draw things once and flip them. Some kind of armature animation would probably be ideal. If it was me, I'd rather do armatures in 3D than 2D, but then it probably wouldn't be in Flash.
Flight/Toss the Turtle
There's an entire class of games, like Flightand Toss the Turtle where you hurl something (or someone) into some kind of level and watch them bounce around until their momentum is used up. You get money for how for they went and buy upgrades to make them bounce farther next time and repeat until you're reached some kind of distance goal. I've thought for a while that this strategy of game mechanic could be applied to any sort of quick casual arcade game, so by the same logic, why not use it for hentai?
First thought is that you play as a guy having sex and instead of increasing your throwing distance, you're increasing your sexual stamina. Lasting longer could allow you to initiate more sexual positions. Getting lots of money or points or whatever could unlock additional ladies to fuck. Or you could reverse roll and play as a lady of the night, increasing her sexual abilities so that she gets paid more by her clients or so that she can do more clients in one night. These games have some kind of mechanic where you can change what's going on slightly, and not just sit and watch. For sex, maybe you can match some kind of rhythm or some kind of power up could float across the screen that you should grab. Or you could something really weird and just keep it a physics game where your character fucks or gets fucked by colliding with things. Or maybe the physics game is not the sexual part, but allows you to unlock a sexy gallery later.
River City Ransom
If you're a video game fan, I'm hoping you've seen this NES classic or its GBA remake. River City Ransom was a beat 'em up game, but unlike all the other linear brawlers, RCR had a lot of RPG elements, letting you explore River City at your leisure, level up your stats by eating various kinds of food or reading different magazines, and collecting extra characters to join your posse, which I did not realize the first several times playing RCR because whether or not new characters join you is based on your reputation, a hidden stat which is impacted by doing cheap things like hitting people from behind or beating on them while they are down or punching the bosses while they are in the middle of delivering their monologues. In fact, if you have a particularly bad reputation, characters who would join your crew will fight you instead. Unfortunately, that goody two shoes Nintendo didn't add any characters that like you better when you're bad (or if they did, I never found them) but that's something worth adding to a hentai remake.
So I've always felt like the combination of sex and violence is difficult to master, but by now we've seen a few hentai brawlers that work, like Furry Fury and sort of Corta's Splatformer. I would be interested to try some kind of game that has beat 'em up esque gameplay but isn't actually violent. Like, instead of throwing a punch you wink and shoot a heart or squirt a tube of lube. Different mechanics would make more sense depending on if you play as a man seeking women or a woman seeking men or a tentacle monster seeking whatever and so on. Given that this is River City Ransom, there's plenty to do besides beat people up, so it's also conceivable that all the hentai happens outside of combat. Gang fights could be your source of money, which you spend on whores back in town, or to woo girls dating sim style. You could rescue girls from gangs, and then bring them back to your place for fucking. Either way, where RCR had stats like Punch or Tough, Hentai RCR could add stats like Charm or Beauty to help attract or please your mates.
While RCR was set in urban japan, beat 'em ups and hentai have spanned a myriad of settings, and I think a fantasy or sci-fi or pirate or whatever style setting would work great for a hentai RCR beat 'em up.
I've actually made lots of beat 'em up games before, though never a hentai one. But since those days, I've realized that I really really hate programming. So I'm not going to try to program any more beat 'em ups myself, but if you feel like you might want to try programming a beat 'em up yourself, I'd be more than happy to explain how they work. Fair warning, I only know AS3.
Prospector
I'm sure you've never heard of this game, but Prospector is one of my favorites. It is a simple premise with an interesting twist. You play as a prospector in space. Your job is to land on planets, map them out, hand over your maps to interstellar corporations for cash, spend the cash on new equipment or buy yourself a small planet to retire to. Along the way, you'll encounter lots of deadly aliens, angry space pirates and inconvenient magma that will probably kill you off every time you leave the spacedock. You can also make cash doing other jobs like transporting cargo, gambling, raiding convoys, mining for resources or capturing space animals to put in space zoos.
So, where can we add fucking? The problem is that Prospector is really a space adventure simulation rather than a straightforward video game, and space adventures can have sex literally anywhere. "We've discovered a new alien life form that says hello by fucking." "The space captain wants to see your in her space cabin. Lube up." "I may be a robot, but I've been programmed with a variety of ... techniques." "The ship's computer is gone haywire and is fucking all the crew!" "This is a rare flower from the planet Gyratos. Its aroma makes people lose all sexual inhibitions." "We're delivering a shipment of dildobots to the colony on Sercuitos VIII." "I can't believe we're crashlanded on the Planet of Groping Tentacles! What luck!" "On my planet, women fuck other women all the time." "On my planet, it is obscene for a woman to wear clothes!" "The breeding season for my species is close approaching. Soon I will be completely overcome with sexual desire!" "Space amazons!" "Hey, R2-D2, do you have a dildo in one of those compartments? Beep peep boo beeb!" "This button sets the raygun to kill, this one to stun, this one to inebriate and this one to evaporate clothing." "Well, I've got no idea what they're saying, but the scanner says they're totally fuckable." "We are Borg. Prepare to assimilated. Resistance is futile." Rancor type creature fucks dancing girls instead of eats them. Jabba type creature fucks slave Leia type creature. Sarlacc pit. Darth Vader uses force choke on pussies. Ewoks have giant penises.
The ideas are as endless as space itself. As long as one had a good way of presenting the simulation, any of these adventures could be added in. The main difference is that Hentai Prospector would need more graphical displays, assuming that 16x16 graphics and text would be disappointed for space hentai. If I were going to reprogram Prospector for hentai, I think I would be content to skip the entire space-combat mechanic, since I've never been able to figure out how it works anyways. Combat in general could be played down in favor of more ... diplomatic options. In fact, the whole prospecting mechanic might be a little tedious if the player's real goal is alien pussy. You'd want the exploration to focus more on meeting new people (new life and new civilizations) rather than on making maps and digging up transuranic elements. Maybe you could fill out a kind of pokedex of alien babes. Maybe the idea is to recruit more space babes to join your crew. Maybe do something like a space brothel.