Twilight's Science Class

The train pulled into the Crystal Empire station, seeing a number of ponies disembark, including a happily trotting Twilight Sparkle, levitating a suitcase full of science next to her. She headed into the Empire proper, right for the castle.

Cadance greeted her, the pair doing their ladybug dance, Twilight even more giddy than usual. They embraced, "Oh Twilight! We missed you!" Cadance sighed, the mares trotting into the castle and into the ruler's private wing.

"Your brother's been going on and on since we got your letter- and i cant blame him!" she laughed.

Twilight nodded, "I'm glad you're both so happy to have read it, I was a little...anxious," she admitted.

"Well I think it's a great idea...and well, this'll help both you and Flurry Heart now, and whatever alicorns come after you."

"So, you already..."

"Yes. Shining wants to raise Flurry first, so it's just me today." Cadance grinned.

Twilight smiled, "Well that's good. And I...might already have ideas for you." she admitted, as they entered the Crystal Castle. "Which is what this suitcase is for-it has so much in it!"

"So, Twily...I was thinking. I kind of have a last request, I guess?"

"Oh of course! Anything, Cadance. You know that."

"Good! I want Shining to be fucking you while we do this." Cadance announced, Twilight fumbling her suitcase, stammering. "What? You've done all this, but you don't wanna get some biology going?" she teased the smaller alicorn.

This gave Twilight pause. She had done a lot...so many things, all in the name of science...so why not this? After all, Shiny had proven he could father alicorns, and that could be useful... "M-maybe," she stuttered, giving it a good think.

The pair trotted into the hallways, heading right for the royal couple's bedroom. Twilight took that time to muse over everything she'd done, and planned to do. Planned to do...that could wait. A nice break, making many little alicorns with her brother. She blushed at that, then shook her head. Focus! Science time!

They arrived at the bedroom, Cadance trotting in excitedly, followed by a blushing Twilight. Shining was waiting for them, wearing nothing but his fur. He grinned at Twilight in a way that let her know he was in on it, too. She shot back a matching smirk, and turned to Cadance, putting her suitcase down.

"Alright. Mostly I've tried stress tests on bodies externally...now I want to see what happens when too much stress is placed on internals. But you're my sister in law, so I wanted to do something you'd enjoy too and well...it suits you being the Alicorn of Love. Basically...I'm going to use both magic and science to induce orgasms beyond what your body should allow, until your heart gives out," Twilight explained, Cadance doing an excited little dance.

"That sounds amazing! How do you want me for this?" she grinned, snoot to snoot with Twilight.

"On the bed-I'll need to tie you down so you don't spoil the experiment." she explained. Shining chuckled, floating out bdsm gear from a dresser.

"Like this, Twily?"

"Oh! Uh, um, yes...can you truss her up then while I get the gear ready? Oh! And she'll need a bridle with a bit so she doesn't bite her tongue." she explained, Shining nodding.

He trotted over to his wife, and began. He started with the bridle and bit, Cadance sticking her tongue out to tease him, giving him bedroom eyes. He smirked, running a hand down her neck and to her chest, taking her peytral and moving to her fore legs, placing the in a spreader brace. With a playful nibble at her chest fluff, he moved to her wings, gently folding them to her sides as they'd sprung up in excitement. He belted them to her sides gently, not wanting her to chafe or hurt. He moved to her hind legs, nipping at her cutie mark in a way that made her tail lift. Her back legs were restrained as her front ones were, with another pole between them to hold her steady. He grabbed her tail last, tying it to a ring on the back of her bridle, keeping her head and tail up.

Twilight nodded, a number of items floating in her magic. "That's perfect, Shiny! Okay, now, Cadance...this first one goes in the vagina. It's got a plug at the front to hold it in your uterus, so you MAY feel a pinch as it goes in. The second one goes in the anus, and that plug's very wide. I'll be as gentle as possible, but if you still tear, don't worry! I'll remember to note it down." Cadance could only moan in response, even as she tried to wiggle her bottom to encourage her.

The first one was pressed into her warm, wet folds. It was very large- her labia spread around it, stretching her out in a way only pregnancy had managed before. She whimpered, wiggling very slightly. Twilight's tail was up, her legs spread wide, enjoying both what she was doing and how it hurt Cadance. Twilight thrust the first device back and forth, Cadance bleeding slightly. She noted this down, before finally pressing it deep within, and once she felt the cervix, pulled back before slamming it in and continuing to press it in. It went in with a pop, making Cadance scream around the bit, and Shining mount Twilight.

Shining's cock pressed against Twilight's cunt, his flat head large and demanding, before he simply thrust it in. "OW! Big brother, it hurts!" she complained, almost dropping the things in her magic.

"Well of course it is. You need some data on yourself, right? Now get back to multitasking," he instructed, taking long, hard strokes to her own cervix and back. She whimpered, it hurt...but it set her afire at the same time. She nodded, and began pressing the massive buttplug into Cadance, who screamed and tried to thrash away. Twilight began thrusting this one too, matching the thrusts from her brother, each thrust getting a new muffled scream.

She finally jammed it in harder, Cadance's asshole tearing as it lodged in deeply. Twilight moved bullet vibrators to Cadance's teats, using a spell to be able to press them inside her nipples, clamps keeping them in. With another spell, all four of them began to pulse and shake, pleasuring Cadance as the magics already in them would keep her cumming.

Twilight took notes as her brother kept using her, fucking her like a fleshlight. Twilight had to admit it was getting her off. She moved her hips back onto his cock, mewling, as Cadance joined her in moaning. The vibrators in her teats were amazing, the ones in her ass and pussy stretching her out and filling her so much, each inch they touched pleasured. She gasped, cumming, hips shaking. Twilight whined, about to join her, before her brother shoved his fat cock right up her asshole, ravaging that even harder than her pussy. She began to cry, it hurt- but the fact she now knew how it felt for some of her science partners turned her on much more.

As such, she did manage to cum, screaming in pleasured pain, her pussy gushing fluid against Shining's legs. She kept moving back onto his huge cock, her own asshole bleeding down her legs. Shining couldn't keep it in, watching his wife have another orgasm, as he fucked his sister, border lined raped, made him need to cum so very hard. With three good, hard shoves, he came right in her asshole, and pulled out to spray the last down her back. He staggered back, sitting on his haunches to catch his breath, Twilight doing the same as she wrote notes on both how Cadance was holding up, and on being fucked so roughly by her brother.

Cadance had hit the sweet spot where she was simply coming constantly, aided by the magic in the vibes. Twilight crawled close enough to put her hoof on Cadance's chest, taking her heartbeat. It was racing, Twilight grinning. She cast a spell, her magic aura now directly above Cadance's heart and attached to Twilight's hoof so she could keep an eye on it. She turned to Shining, "Alright!" she chirped, "Your turn!"

Before he could ask for what, she'd grabbed him in her magic, said magic clamping down on his own so he couldn't fight back. She cast another spell, giving herself a massive, long horsecock. "Open up that mouth, big brother! If you don't, I'll have to make you...and I really wanna make you," she panted.

He opened his muzzle reluctantly, not as fond as being on the receiving end. Still, he didn't want his sister to decide he could be an experiment anyway. She took the invitation, and holding his head steady with her hooves, shoved her cock down his throat to the base on the first thrust. Hooking her forelegs behind his head, she raped his throat with reckless abandon, making him gag and cough. Al it did was make her hornier and massage her length. She pulled out just to cumshot in his eye, pressing her cumhole right on his bare eyeball to do so.

He screamed in pain, trying to thrash away. "Oh big brother! Keep that up, and I'll have to fuck your eye out of your skull, you scream so sexy!"

He gritted his teeth, trying to keep silent. She finally puled away, leaving him to try to blink spunk out of his eye. She moved Cadance so she was at his rear, to the side, getting a good view of his balls and asshole. Twilight seized his hind legs in her magic, spreading them wide. She pressed her muzzle to his asshole, lapping at his ponut, sliding her tongue in deep.

Cadance did her best to watch, as her vision was going shaky and her heart was racing at a painful pace even as waves of pleasure rushed over her. She watched as Twilight mounted her brother, thick magicock at his entrance. Cadance had always wanted to see his asshole ruined from a big fat cock, and Twilight being the one to do it got her off harder than before. She trembled, clinging desperately to life just so the last thing she saw was Twilight getting off in his asshole.

Twilight arched her back, slamming her cock into the hilt, making her brother scream. "Nnngh, fuck yes, scream for me! I love the sound..." she reached forward to pet his mane, "It's alright, I'll make up for this...you and I are gonna be making alicorns for years! Together, with others, and when they're old enough...more science!" That did seem to calm him, enough to relax and start enjoying the buttfucking.

Twilight took long, deep strokes, tapping at the bend of his intestines with each one. "Oh this is amazing! I should do an entire series of science on incest!" Cadance had to agree, even as her breathing became more labored. Twilight took notice, "Big brother, look! Your wife's heart is collapsing from too much pleasure! Isn't that so hot?!"

Shining had to agree, the look of ultimate pained pleasure on his slutwife's face was amazing, almost angelic. Twilight redoubled her thrusting, ass bouncing, Shining rolling his hips back to take it all. They watched as Cadance trembled, eyes rolling back and teeth clenching on the bit in her mouth. Her bound wings tried to flap, struggling in their bonds, before she went stiff, and then limp in her restraints. Twilight cried out in delight, "She died! She died from cumming so much and -" she whinnied, cumming herself deep in her older brothers asshole as he shot a load onto the floor.

Shining looked over to grin at her. "So...alicorns and incest huh?" She grinned back. "Maybe..."