Gnash your teeth like a flamingo swarm
"Hey, Anon. Do you wanna try that thing today?"
You're lying in bed with Twilight Sparkle, all floof and purple princess over the side of the bed. She's lounged out like a cat on the sofa, kicking her hind-legs idly, eyeing you from less than a foot away. You can see her squishy, lilac butt from this vantage point very nicely.
"Yeah," you say. You turn over on the bed so you're lying on your back, propped up on your elbows behind you. You put away the Pony Penthouse Monthly you were reading in the desk drawer.
Twilight is turned around too, and smiling at you.
"Shall I do the opening honors?" she says, grinning with a wink.
"By all means," you say.
Twilight's horn glows, and you feel your clothes being lifted off by magic force. Shirt over your head, pants unzipped and buttoned and dragged off your legs, thrown into the laundry bin in the corner of the bedroom. Underwear follow, until you're totally naked.
Twilight giggles when she sees you're already half-hard.
"What?" you say. "I've wanted to do this for a while."
"Lay down then," she says. From underneath the bed, she levitates out a pair of sciencey-looking goggles, and straps them on her head over her eyes. They're not necessary, but it does add to the experimental illusion all the same.
"Arms up, behind your head," she says, prodding one of your arms with her hoof.
You move as instructed, stretched out from end to end on the human-sized bed also fit for a pony.
Twilight hops up onto you, mounting your stomach and pressing the cheeks of her butt into your erect cock. She wiggles from side to side, slapping your dick back and forth between her cheeks and getting a glob of precum stuck in her fur. She giggles and prods the spot on her lower back with her hoof, then brings it to her mouth and licks the tiny bit of clear fluid from it with her long, extended tongue. She licks her lips afterwards, gives a satisfied-sounding moan, and smiles devilishly at you.
"Ready?" she asks.
You nod.
"As ready as I'll ever be."
Twilight lifts her butt up and hovers just above the head of your cock, swaying back and forth and dripping little droplets of her mare-juice onto your head and shaft. The heat and wetness are palpable from inches away, then centimeters, then you can feel her lips touch the tip of your cock and begin to slide over it, letting it in and squeezing the whole way down, until you're buried in her cunt, and she's planted firmly on your crotch and moaning and clenching you with her pussy, and this is only step one, keep in mind.
"Fuck that feels good," you say, almost involuntarily. Twilight bobs up and down a little on your dick, just an inch or two, rocking back and forth and making soft slapping noises when her butt bounces.
"Ready for the next bit?" Twilight says. Her face is flushed, and her goggles are beginning to fog from the inside. She takes them off and wipes either side with her hoof, but a few patches of smog and sweat still remain.
You nod. You're not sure you can say you'll ever be ready for something like this. But a nod is doable.
Twilight nods back at you. She lowers her eyebrows and begins to concentrate, clenching harder around your cock as her body seizes with focus. Your cock twitches inside her, and you watch as her horn begins to glow, brighter and brighter, until the translucent purple has bled into an almost pure white light, so overwhelming you have to turn your head and look away before the final flash happens, and the whole room lights up and then goes dim, back to the single lamp-light overhead, and Twilight's horn back to a dim, lilac glow.
"There," she says, panting slightly. "I should be able to do it now."
The tip of her horn shines, and you feel it. Like a hand inside you, gripping from a place poked between dimensions. You feel it reach up through your ass and grab your prostate from the inside, and squeeze it like a tiny, pent-up walnut full of delicious juice—which is technically what it is, anyway. Having it squeezed directly feels like being punched in the dick through your ass, but in a good way, and if that isn't a miracle of description in some capacity we don't know what is. It feels like an assgasm starting in your entire body. And you really have to think about 'assgasm'.
Words come out of your mouth, but you don't recognize or remember them. It takes a few seconds for you to remember how to navigate the remainder of your body while your walnut's being squeezed in a magical vice-grip. And while the pony on your cock is still rocking herself back and forth on your shaft and squeezing you there too. Something like 'Fuck me, that feels...' and then nothing besides incoherent mumbling and groans.
From her observation post on your cock, Twilight seems to take your enthusiastic response as a good sign. Her horn glows brighter, and she starts moving in earnest on your cock, pulling herself up at least half the length and then slamming her butt back down onto your pelvis, the 'smack' sound getting louder, along with Twilight's panting and moans.
And the incomprehensible primal groan coming permanently from your chest through your mouth.
Twilight giggles as your cock twitches rapidly in her pussy.
"Don't cum yet," she says, and runs a hoof over your chest. "We're just getting started."
"Unnhnnnggh...." is a rough approximation of your response. Something intended to be 'go softer' but translated as 'oh fuck i'm gonna cum so hard i die'. And then spat out through a human mouth. Twilight's grip on your prostate finally loosens slightly, but as soon as it does, you can feel another invisible, inside hand begin to wander on its own.
This one travels up the shaft of your cock, and when it travels, you can feel it from the inside out, each time it passes a nerve ending, tickling it and lighting it on fire before moving on. The throbbing sensation coming from your ass through to your dick is dulled, but now the new hand is moving up, inside your stomach and into your chest... you can feel the fingers around your rib-cage, poking and tingle in a way only living through it can allow you to understand, and then you feel the final placement, the slimy tracing of the fingers around the outside of your still-beating heart. Inside your body, Twilight has a hand around your heart.
"I'm gonna squeeze it," she says, and grinds her pussy hard down on your cock.
"Are you ready?"
"Hnnn," is all you manage, and meek thrust upwards to give your cock just a little extra poke into the outside of Twilight's womb.
"Ahh! Mmmhm, that's really good... let's do me next time, so I can feel you squeezing my womb from the inside."
You nod and tap Twilight on the leg with an insistent pace. You're not going to work up the courage to do this again any time soon.
"Right," she says. "Here we go..."
When Twilight's hand tightens around your heart, each of your senses screams in overdrive. You become able to smell and hear everything instantly, then lose the ability the next instant, replaced only with white hot flashes and screaming from the dark, inside place of every pore: help. stop. get us out. anything. please / let / it / stop.
"I'm gonna cum," Twilight says. "I'm gonna cum on your dick."
Squeeze. Lungs no longer in cooperation. Air portioned and rationed long ago. Drowning in a pool of oil. Drowning in a lake of salt. Drowning in thin air, above the mountains, underneath a thousand oceans. Choking, sputtering, head seizing and veins throbbing to explode.
Twilight's hand, clutching your heart, squeezing it tighter with each pulse, bruising the veins with each beat. Each tap on the side of a giant glass window. Tap. Tap... tap...