1: Type/number of rapist/s
For a more personalized story that can still have threesome elements, one or two assailants will serve. To achieve that much sought after gangbang element, anywhere from eight to twenty works wonders. It should be so many men that they start to blur into each other, except for maybe a single ringleader. As for the type of assailant, the aggro, hypermasculine, rough-around-the-edges sorts tend to be preferred. Think of men like Leland Coyle from Outlast, Roadhog from Overwatch, or Immortan Joe from Mad Max. The meaner they are, the more intense the violation.
IMO, the best rape fantasies are the ones where the men are visibly enjoying themselves, though not so much that they lose composure. For many women, the core appeal of the fantasy is the idea of being wanted so badly that the choice is taken away from you; show how good the sensations feel for the assailants, not just how much they enjoy domination. They can moan, curse, suck/lick, and of course come.
2. Type/number or victim/s. How should her mind and body react to the violation?
If there’s just one assailant, there can be any number of victims, tasting menu style. In a gangbang story, one or two victims will suffice, since a small number of victims emphasizes the overwhelming power of multiple assailants. (Unless you’re going for one of those full-scale “new world order/public use” scenarios.)
In my experience, a dichotomy arises between the two most popular types of victim: the ones that are notably powerless, and the ones that are notably powerful. With the powerless ones, emphasis is placed on her inability to defend herself, as she lacks both physical strength and overt intelligence. These girls are usually younger, and have a distinct personal style, though not one in particular: they can be nerdy and frumpy, bouncy and slutty, tomboyish and butch, preppy and businesslike, modest and elegant, anything you want.
With the powerful ones, emphasis is placed on how difficult it should be to overpower her, making the moment where she gets dominated that much more sweet. These women are often older, and they tend to be composed, competent, and arrogant - and like their powerless counterparts, they usually have a distinct style. She can be an icy queen, a muscular badass, a genius professor, or a stuck up boss. Either way, she’s getting stripped and pumped full of come.
An important factor to keep in mind is that, no matter what type of woman you’re writing about, it really helps for the victim’s body to be eroticized and appreciated, even as it’s being violated. Like I said, these fantasies often hinge on desirability.
Regarding the mental reaction, I think you know the drill. Humiliation, intense fear, plenty of pain, and total powerlessness are the watchwords. As for the physical reaction, objectification becomes much more thorough when the choice to enjoy it is taken away from you: usually, the victim can’t help but get wet, moan, whimper and come, often more than once. It’s extra fun when one of the guys comments on it.
3. Preferred locations
Somewhere no one will hear you scream! A sexual fantasy is a world in it’s own right, and the more detail that world has, the better. Y’know how the Hobbit holes in Lord of the Rings are designed to be as cozy as possible? Imagine that effect, but for a place where a girl can get absolutely wrecked with no possibility of escape. A mattress in a basement, a cabin in the woods, a jail cell or yard, even a boat in the middle of nowhere.
4. Single rape or sex slave?
I’m leaning towards sex slave. From my perspective, single rape is only desirable for that long shot of the ruined body when they’re done, and that effect can be achieved just as well in a sex slave story, with the implication being that they’ll come back for more later. Thinking that this is just her life now really adds to the degradation of the whole experience.
5. Should weapons be involved?
Ask yourself what a weapon adds to this fantasy. Is it a little knife you can flash in her teary, wide-eyed face, maybe nick her with a couple times to make her yelp & keep her on edge? Is it a big, phallic shotgun to point at the back of her head when she’s getting plowed? Is it a little pistol you can knock her over the temple with beforehand, to get her dizzy and out of it? This applies to any object you want to involve: leashes, collars, and nooses can also be fun.
6. Should the victim be restrained by pure physical force or by ropes, ties etc?
Like Question #4, this ties into the subject of how long the violation will be going on for. In lots of professional rape fantasy porn, the scene will start out using only physical force before transitioning into full bondage. I think this principle works just as well in a story. If you want to avoid drawing too much attention away from the body with big bulky restraints, a single tie at the wrists and/or feet will suffice.
7. Should there be slow build/tension as the woman realises the situation she’s gotten herself into or should it be a faster paced erotically detailed attack?
Slow build all the way. Erotica is all about tension: maybe start out with a bit of catcalling, groping or fingering before diving in. Even if you want the attack itself to begin very intensely & abruptly, I always love it when a story builds up the lewdness before transitioning into the sex. This effect can be achieved by describing things like how her tits/ass bounce as she walks, how her thighs compress against a chair, how her hair brushes the small of her back; even an upskirt shot, if you’re not averse to cliches.
8. Anything else you’d like to see.
Certain details used sparingly will help other elements stand out. In my experience, it’s all about finding a balance between degradation and sexualization, dehumanization and individuality, pain and pleasure, etc.
When a girl is stripped naked, maybe she keeps on a torn article of clothing, high heels or combat boots, a nice piece of jewelry, something distinctive like that. If she has pretty hair, have someone pull on it or come in it. If she’s a virgin and the penetration is extra painful, put some focus on her clit to keep the forced enjoyment element.
If the assailants are old and she’s young, talk about the grey in their hair. If they’re nasty and she’s clean, talk about how bad they smell. Details about their dicks can help keep the individual attacks memorable, even if there are too many to count: things like sharp curves, big veins, if they’re longer or thicker, and of course how they feel inside of you.
Good luck and have fun.