Shrunken Sister

by B_25

Rating: mature
Tags: Fetish, Spike, Shining Armor, Sex, Twilight Sparkle, My Little Pony: Friendship is Magic
Length: 5055

Twilight has taken an interest in sexual anatomy. This has entailed to Spike being shrunk and sent deeply into herself, at least for a week, composing sketches and taking notes. Now she wishes to do the same herself—except learning from Shining.

Twilight has taken an interest in sexual anatomy. This has entailed to Spike being shrunk and sent deeply into herself, at least for a week, composing sketches and taking notes. Now she wishes to do the same herself—except learning from Shining.

[Cock-Vore so you're in the know.]

[Cover by Otakuap]

Commission for Shadowlynch!

Want a story for yourself? Then check out my commissions page!

Published 2021-01-10 04:10:02 UTC
Last updated 2021-01-10 04:10:02 UTC

I | A Legitimate Examination

Shrunken Sister
B_25 & Shadowlynch

Shining was unable to close his mouth and his eyes were in a continuous blink in pondering the last five minutes of existence. They weren't horrible and nothing, well, disgusting had been said. It was confusion. Plain and simple.

And it was typical in having Twilight Sparkle for a sister.

"Are you still with me?"

"Psychically? Yeah." Shining's eyes shot to a different planet to avoid the gaze of his sister, who stood in front of him, trying to peek her muzzle into his vision. Sometimes he scooted into a turn as she inched closer. "Mentally? Well. You'll have to give me a bit longer on that."

"Please! Please please please! I'm coming to you because there's nobody else I can go to!"

"What about Spike? He's nice and handsome and has your back." He stroked at the side of his jaw. "Seems like he's already used to weird stuff like this. Stuff you shouldn't be telling your older brother." He puffed his chest. "I already did my duty buying you those magazines when we were younger; the clerk looked at me funny for that."

"Shinnny!"

His shoulders dropped as did the act. "Fine fine. Play it again. I'm listening."

He looked back at Twilight who beamed at the attention. His eye clenched at her willingness to do such a thing. It was for a noble cause and the girl, no doubt, was unaware of the deeper ramification to the asked-favor.

"The school is really starting to take off," was the start to the ploy as she began to pace back and forth in place, entering that scholarly mode, one able to make everything, no matter how dirty it was, sound profound and scientifical. "Enough that it may inspire a branch of other schools that'll run off the same curriculum! I need to ensure that every class to every subject is sparkling in its information and what will then be tied to it! Magic and friendship and mathematics! I have experience with nearly everything!"

Shining's head slunk onto a shoulder as his sister struck a hoof to the ceiling. Secretly, he enjoyed the dramatics. It powered more 'oomph' into the day. Of course, though, he had to be mocking of her. Such was the social decorum. "And the stuff you don't? Let me guess. Your friends? Agriculture from Applejack and fashion from Rarity!"

"Indeed! Friends compensate for each other to create a greater collective consciousness!"

Shining huffed. "And this sex-ed class?"

Twilight's pose shattered. Cracking until breaking down. Her muzzle fell as her eyes were cast to the floor. She sighed before speaking. "None of us have been so lucky in that regard. Much less to pure anatomy. None... have really pushed the subject like me."

Now should have been the time for a joke or a cruel remark or something of the sort. But Shining just didn't have it in him. Instead he huffed, exhaling his dread, any tension as so he may comfort his sister. On matters abstract and absurd, she was mostly alone, easily mocked, without another willing to understand.

And he was her big brother best friend forever for a reason.

"Come over here already." Twilight looked up in time to see her brother holding up an arm, the space next to him, now open, which caused her to smile. Slowly she came to him but quickly she snuggled into his side. He ruffled her mane with a hoof. "Now tell me more about this. What do you mean you've pushed sex-ed further?"

Twilight froze in nuzzling his neck. She faced forward with a blush. Breath held and shock repressed. "Well... there hasn't been much research on the study of, well, sexual anatomy and... yeah." She wiggled deeper into him, even if only, to get further away from his gaze. "Interior anatomy is limited in description and drawings. Usually... they're performed on the deceased. But... but that's limited."

It didn't take long for it to click. Catching on to the little things showed that one was not only listening, but learning, being improved in so doing. One nugget of proof that someone's explanation had worth to snowball them in that regard. "Because those are organs while they're not functioning, right? So it's not all natural and, well, living.”

She snuggled into him happily. "That's right! There's no depiction of the full extent of the anatomy... much less while it's in action! But I want the school to be different. Most ponies can get away without knowing what goes into sex." Twilight's mane rubbed into his coat as she shook her head. "But I want the option to be there for someone to know every function that happens to every aspect!"

Shining still couldn't help but chuckle as his arm wrapped around his sister's barrel, holding her closer, tighter, while rubbing at her wing. "Guess there's something noble in that. So that's the reasoning for the shrinking spell?"

Twilight nodded. "There's no other way to see, um, t-those areas in full scale, to greater detail, without someone being, uh, reeeally small. B-But you should see the drawings!" Her horn glowed from the corners of his eyes and, before he could turn, already a series of scrolls exploded into existence. "I tasked Spike with shrinking and going inside of me. Had to lay back in bed and keep my legs parted and let him climb in himself. See this?"

Shining wasn't sure if he should be seeing any of this but, already given that morals were out the window in all regards, he went along with whatever his sister wanted. Looking forward showed the scroll depicting two barrels of purple, each composed of utter softness, leading into a cliff that was a crotch.

"He equated it to mountain climbing! Tickled a bit feeling him on my thighs and he sunk into them pretty well! Nearly bucked him a few times. Knowing he was going to climb inside there—"Twilight pointed to the cavern of a pussy as the towering slit seemed ancient in its greatness "—was nearly enough to lubricate me! He took a break and did another sketch from my thigh. Here it is."

The next scroll shuffled in front to reveal the lofty gates of femininity, large and thick and voluminous, doused in spilling liquids. Fur catching to stickiness as the gap between the lips greatened—knowing who approached it.

"He has quite the claw and eye for these kinds of things! Looking down at it... that area means nothing to me." Twilight tapped the parchment. "But seeing how it's depicted here... it just gets me going! It looks and feels so great! Knowing that it was going to take him inside for such a long time... I promise, from your angle, you'll like this a lot too!"

Shining flicked his muzzle to hers in a glare. "I thought all of this was for scientific research for the betterment of education!"

“But it is still exactly that!” Twilight retorted with a smile, shame replaced by arousal, sex one heck of a drug. "If I didn't let myself feel everything that goes into it... then it wouldn't be accurate research! But here." She flicked through the scrolls and Shining nearly regretted his outburst. "We can get straight to the point. Check these ones. There's more medical."

Spike must have had a desk and other supplies shrunk down and brought to him inside Twilight's cunt—the manner of how, of course, a delicious thing to ponder—due to the quality of the work. Indeed the art seemed to breathe. Living and pumping. The cavern, alive, in how it expanded then contracted. The shape and curve of the walls and how the ceiling of flesh seemed to be one with the sky.

"That's... actually kind of interesting." Shining inched his muzzle forward to intake all the little details one would never know existed, cocking his head at a few, eyes tightening to work out what items were. "You never actually see inside of one. Much less this much detail. Kinda clueless on what some of this is."

"Exactly! My point exactly! I want everypony to know everything about themselves! No matter how little or its location." Twilight rolled up the scrolls before they puffed out of existence. She then scooted to the side. "I'll save you from the rest of them. There were a few more details about what it looks like when a mare—u-um, y-y-you already know."

Shining swallowed and nodded and was doing his best to not feel a million things.

"He ended up spending a week in me to record all the possible contexts and ways that area interacts with normal life. Bath time was a bit more interesting than usual. Sleeping was harder knowing he was inside of me. It was constant teasing really." Her shoulders slumped. "Although I didn't get to do everything I wanted to."

Shining blinked. "I... can't imagine what would fail to fit into a week of doing... what you just said."

Twilight rolled her eyes and then sighed. "Well. One of my interests was having Spike down there while, y'know, I was having sex with someone. But not only could I not find someone who would be willing to go with the idea... Spike, well, he's like any other dragon. Or guy for that matter."

"In what way?"

"That he doesn't like the idea of being pounded by some other guy's dick while being stranded inside a pussy."

Shining went to nod before stopping, forced to blink, reset his mind. Being with his sister was never easy or straightforward. It was like living in a different world of logic. One had to take it to the chin for there was no greater crime than upsetting his little sister. "Y-Yup. That's the case with all guys. We hate it when that happens."

Her annoyed face and eyes shot at him. "Are you making fun of me?"

Shining squinted an eye. "Little bit. But it's true. Most guys wouldn't be willing to do that... just like how they wouldn't, uh, take someone into, well, their private thing."

"You can say dick, Shining."

Shining's shoulders collapsed and his face took to mock. "C'mon Twilly! That whole time you were avoiding using the word pussy!"

"Because the air was still awkward!"

"Is it any less awkward now?"

"I... I..." Twilight's shoulders dropped. "I hope so?"

Shining sighed and lowered his head. Time to try again. He raised with his best attempt at a smile. "Then yes. Most guys would be a little off-put in being asked by a shrunken mare to go inside their balls."

Twilight was sitting opposite of him on crossing her forelegs. "Spike had no problem agreeing to go inside my pussy! Sure I had to offer him vacation time afterward. But he stayed inside of me for a week with little issue! And I didn't mind it! In fact I enjoyed it!"

Shining winced at hearing that, once again not throwing an insult, knowing the damage it could do. "And you couldn't ask Spike to do this for you?"

"I would... I really would.” Twilight took a breath to descend from her high as the connection between them was broken. In collecting herself, she tried again, choosing to speak from the heart. "If there was anyone else in all the world I could trust with this, I would have gone to them first, all to save you from this."

Then she looked at him directly. "But none else comes to mind. Spike's a dragon and, while studying that will be eventually on the list, I'm focusing on ponies for the moment. Not only that. But what if lust, like greed, overcomes him? He could trap me in his balls and never let me out."

Twilight's shoulders dropped at the thought—and so did his. "Always trapped at his crotch and smacked around. Forced to always be inside of him and in such a place. His cock would always be dangling above. If he chooses to run or jump or slap his junk around—any stallion I asked for this—I would be helpless."

Shining chose to look down at his crotch this time around. Seeing his flaccid shaft between the snowy banks of his thighs. What did he have against this again? Never did he want to see his sister harmed. Trusting her to another stallion, to another guy, scared him in the instincts that might take one over.

It was his love for his sister, after all, that would stop him from doing anything foolish. "You'll be safe in there?"

"Spike lived inside of me for a week and used his flame to get stuff out to me." Magic infused Twilight's horn as a saddlebag popped into existence. It flipped open as vials containing potions floated out. "Zecora helped me with these. One to shrink and one serves as an antidote for that. Beyond that. They'll provide oxygen to my blood so I won't have issues breathing in there."

Twilight pointed a hoof at his crotch and, he, a filly in a colt's body, covered his junk with hooves, closing his legs, and pouting. She laughed at his blush and sat down herself. "Most of my magic will be reduced with my size. I'll be able to do some spells. But they'll be relative to my surroundings."

Shining's eyes narrowed as he sensed the incoming joke.

"So while I'll still be able to levitate some items... I wouldn't be able to lift one of your balls in my magic... for instance." Twilight covered her mouth and laughed into her foreleg. Shining couldn't do anything to fight this. "So I'll be safe inside of you. Might get jostled around a bit. But males are already pretty careful in protecting that area already, right?"

"I guess—" Shining clenched an eye "—it would be the safest part on me."

"Exactly! I'll go inside of you for a bit, learning all that I can, do a few sketches of the organ in function—then at an agreed time, you'll let me out, give me this potion, and... we'll agree to never talk about this again."

Shining huffed as his legs spread and arms pulled away. "So you do know some shame after all?"

"Hey! Spike got to enjoy me a lot and I thought I was going to get to do the same in return! Haven't seen the little bugger since I let him off for vacation." Twilight stood from the ground and floated the bags onto her back again. "I still need the full scope of one's feelings and reactions to all of this. I was hoping to find a decent guy to test all of this with but, well, it turns out he became you."

Shining struggled to keep his smile on. "This isn't going to ruin our relationship, is it, Twilly?"

"It'll make it a little strange for a while." Twilight had gone to the door but stopped before it, blushing, the act hidden as she turned away, her mane covering her face. "But we should both try to enjoy it. Somewhat. Just for the sake of accuracy."

"I'll try my best in that regard, but uh, no promises."

"And Shiny?"

"Yeah?"

"Please don't tell anyone about this? Don't think anypony would look at me the same after this." She pushed the door to the room open, stepping through it, but pausing halfway. "That. And I don't think I could stand Cadance, knowing I'm small and inside of there, to be looking at your balls. She'll tease me."

"Twilight."

"Yes?"

"I want the same as you as to have no one knowing I let my tiny sister inside of my balls for a while."

"Shiny?"

"Yeah again?"

"You really are the BBBFF a sister could ask for."

The door closed after that as hoofsteps echoed from the hall. Shining sat there for a moment to collect his thoughts. No matter what, he had to say yes, for the sake of her. But looking down, he saw his cock, flared a little, his balls a little more pronounced. Soon they would house his little sister. Trap her within their depths.

The strangest kind of prison.

"Am I just as weird as her... or super accepting?"

There'd come the knock at the door, four with two seconds apart, the sign asking if this was ready to begin. Shining rolled from his head and landed onto his hooves, dressed in a robe of blue, already freshened up—as much as able considering the context.

He reached the bedroom door and pulled it back. Twilight stood on the other side, smiling, though looking at the ground. She pawed at it with a hoof, equipped, still, with the previous saddlebags. Shining spoke up. "Cadance gone then?"

"She stayed for a bit to catch up before heading out—exactly as we planned." Twilight rose her muzzle and fought to raise her eyes beyond his chest. Her vision dropped to between his legs. That didn't help either. "W-We should probably do this quickly. You have to be off soon. May thee bedside counter?"

Apprehension still had him. His heart thundered and hers must not have been much better. Electricity shivered in the rim of his hooves as they were actually going to go through with this. The mare passed him to the bed, and he was a step behind her, deciding to lay back on the mattress himself.

Twilight stopped before the counter and floated out the potions, all of them this time, though paused on floating out the third one. "That's strange. I still have three? I needed two antidotes... though maybe... she gave me three?"

Shining cleared his throat as he rolled onto his side from the bed. "Twilight. We don't have much time with this. You have to get inside my..." He winced and looked down at between his legs. Seeing his cock with his balls draped on his thigh. There was the resting place she needed to get inside. "Let's just try to do this as quickly as possible so we have enough time for the hard part."

Both of them froze and, after dealing with enough anxious air, the two instead laughed, helping to quell their nerves. With everything set on the counter, and levitating the first glass, Twilight popped the corked, putting the rim on her lips, head tilting back, drinking creamy scarlet.

It took a few seconds for it to go down and, once it had done so, the mare stumbled back, catching herself—Shining reaching out to her anyway. Twilight met the gesture with a smile on placing the glass back on the counter. She looked at her brother. "You ready for this?"

Shining nodded as best as he could. "As ready as I'll ever be."

"Thank you."

Twilight could feel the coldness spreading across her veins, slowing her blood, freezing outward rapidly. Frigidness tightened into itself beneath the skin, imploding, a swirling ball of frost pulling everything into it. Bone and skin and muscles. Everything tightening into disappearing as the mare started to shrink.

And already she was the size of a filly in reaching the side of the bed. She hopped in place, cutely, the sounds childish. She retained the same physique, now smaller, as her forelegs hooked over the mattress. Fighting to pull herself over, Twilight sensed a shadow passing over her face.

"I-I'm okay! Let me do this!"

"I... if you say so."

That voice. Loud in its booms of causal masculinity. Twilight had hardly rolled onto the bed when her legs shrunk from its edge already. Quickly the blanket was spreading and spanning a growing desert. Clumps of dense fabric, rising like hills and dunes, softness and blue.

Something had slid out to her sides and she was taken into a shadow at once. Her form limply laid on its front as she compressed into herself. Raising her chin from the ground, she looked around, to the sides, seeing the monolithic.

Indeed it had been a view. Blanket spanning a field until losing detail into the territoriality of the shadow. Deep in the darkness, there was a curve, one of white, so bright as to be seen. It arched upward, its mass incredibly thick, a mix between muscle with plushness coated over.

And another impossible and identical site rested to her left.

Twilight was forced to breathe deeply in seeing the scene. Stumbling to her forelegs and shaking the tension out through her hooves. She'd been caught in a valley, in its middle, where light shone over the bend of the creamy cylinders.

Ahead space narrowed. Shadow from either side joining at the half-point. There rested something in the distance, truly a living cliff. It was a crotch of white, vast and untamed, rising, around the start of the thighs.

And there rested the massive orbs of ebony. Boulders didn't compare to the monstrosities. Density of black, utterly stretched, in the magnitude of the encased globes. Indeed each was like a world, a planet almost, contained within that sack. How it could house a building after building, a city almost, beyond the leathery skin. It was a thick dome that could easily make a home for life.

Twilight was beckoned to the balls in a strange fear of the appeal of the spheres of masculinity. Overhead them and like a bridge was his cock. Limp yet hung. Starting arch in its 'smallness.' It reminded her of world-size serpents able to devour cities.

And wasn't that the case with this? The thighs on either side, their white, dimmed, by the shadows they cast... losing to the rich blackness of the massive privates? The twin balls stacked like mountains as the cock above served as the weapon to such things? So large and spanning, size and girth, length and arch, escaping from and blurred in her vision.

Massive gales blasted across the fiber landscape and nearly blew the mare back. Twilight gasped in holding a foreleg to block the winds. Her snout twitched in the scent. Musk. Rich and pervading. Enriching her lungs was a stink that was somehow delicious.

And when she pulled away her forelegs, Twilight found herself in a deeper shadow, the feeling of weight looming in the sky and, when she set to look there—ended up shuddering into herself instead. There sprawled from the distant sack, at a height and distance fully blurred, was the starting thickness the colossal cock.

Nothing could be seen beyond its flare as it consumed the space of a cloud. Its thick borders like walls that couldn't be scaled. In the middle was the slit. Four times her size in every regard. Easily that mouth that could devour her, through the scale of the massive and throbbing thing, to the twin cities it connected to.

The cock, that monster, serving as the entrance, in devouring a prey, to the balls so utterly massive as to be beyond description. Twilight was awash in heat. Temperature from herself and the world rising. Heat rolled off the ball and floated over in promoting a beach-like paradise. She melted in being faced before a giant sex. Easily those balls could rise into the sky, dangle, before dropping, crushing into her, smothering her in the vast sack, rolled around by the heft of the round mountains inside.

Used like nothing more than a toy.

Or forced to cling to that massive member and not allowed to let go, forced to serve and worship the stallion it belonged to, uncaring, so long as he had a mare wrapped around his junk. But Twilight shook her head and looked up. All fears, quieted at once, in the face looming in heaven.

Shining's chest loomed higher than high as his chest spanned beyond the sky. His face orbiting like the moon as its details became fuzzy in sacrifice for the whole. Seeing someone small was one thing. But being the one tiny, weak and powerless, and cast to the massiveness that was normal for everyone else.

It was scary.

Yet Twilight's brother was there.

Shining felt awkward in having his sister between his legs, much less trapped as she was, the view enough to start his erection. It bent in a low arch and leaned over the mare herself. The purple inch looked up at him and, though her form could be made out—her face was lost to the difference of their sizes.

He kept himself still and ready as the mare reached his crotch. His hoof scooped down to help her but, in a second, there came a squeaking in his ear. "N-No! No touching! I have to do everything myself!"

Shining's eyes flicked left to a tiny glowing swirl present there. His sister's magic. It flickered in weakness as even though amplified—she was hardly heard. "Are you sure? That's quite a trek."

"Y-Yes! Please!"

"...alright."

Shining sat back and huffed and was mindful of the storm he just cast on the girl. Looking down with a squint, he saw her reaching his balls, her hooves glossing on the curve of their front. At once his cock flicked upward at the touch. He had to concentrate to feel Twilight's hoof, but in focusing on that sensation, it made him more sensitive to it.

Barely he could feel the ticklish winds of her wings as they beat and lifted her from the ground. Her hoof kept on the orb in following up and over its curve. She disappeared underneath the view of his dick, its size and width hiding her underneath it, that was, until she floated up from its side.

She came to rest on the base of his crotch, before the start of his dick, which expanded further. The mare took a moment to drink the scene. Sitting down and looking up. How the width of his cock, its staggering height, escaped every corner of her eyes. Nothing could frame it. Only tease to how so much more meat remained to the staggering impressiveness.

"I... I think... I think I'll need your help on this one."

Shining clenched his eye and endured another throb of his cock. There was a delight in knowing his sister sat before his joy, so nothing in comparison to it, wanting to follow that dynamic more. Still. That was his Twilight down there. And he had to keep himself in check. "W-What do you need?"

"Just need you to hold yourself up as much and as straight as possible." Shining followed the request as the words buzzed into his ear, hooking his wrist around the middle of his pride, holding it up. There his head faced the ceiling and served as a platform. "Just like that. It still doesn't feel like you're full yet. I'll... try to do some teasing on my flight up."

"T-Teasing?! Twilly! What do you mean—"

Pleasure compounded in a bite of spreading satisfaction someway up his shaft. There'd been a tickle building into greater pressure of the pleasure rose. He squinted through frosted bags to his cock. The vein pumping and protruding from the skin. There was the form of the slender girl. Draped over the vein, riding out its pumps, satisfaction rocking her, Twi humping, thrusting, grinding, back and forth, while her wings beat, tickled and brushed across his stuff.

Much less her muzzle dug into his stuff. Kissing and licking and nipping at the meat. It was that concentration of extreme pleasure that rocked the mare from the post. How his dick shot into full mast, painfully hard, a flick to an ache, the need to get off quickly.

But not that he would be finishing.

Instead through cracking open an eye, he watched the purple fly of the pony rising, landing on his head, the stage that was his cock. She touched down on his circumference and her itty-bitty hooves sunk into the lax flesh of that. Twilight strolled around, slow and looking at the surroundings, seeing how the ridges rose, reminding her of banks, how they capped the view of the world beyond.

And Shining couldn't help but throb at all of that.

"W-Woah!"

Twilight shuffled on her hooves in every possible direction as the blackened and soft ground rocked back and forth, a lean to the left, followed by one to the right, a quake that broke through the density of the tower. The feeling of being on something powerful vibrated into her hooves' bottom. Feeling of blood pumping across the orifice. Its throbs of hardness able to break through everything.

Everything stopped after a few seconds. Twilight twirled around and looked up. Nothing but a speck on the head of his dick. His belly spanned afar, chest shooting up, head in the stars rocked back. Shiny's eyes were closed and his expression was of reassessment. "T-Twily... you... may want to get in there quick."

Another bob accompanied by a thrust as the poor boy couldn't stop from holding himself back. This one inched the shaft into the air as his hips had flicked with the movement. His forelegs were holding his cock as best as it could. But even in its imprisonment, it beat to get out.

Twilight gasped as the disc of black rose from ahead, the ground tilting beneath her hooves, which slid with the momentum. The stage became straight a few seconds later. Lack of grounding teased from behind her. The mare twirled to see the gap before her, a slot going deep, revealing a chasm called the beast's entrance.

She peered over the edge to notice the smoothness inward. Though it was hard to see, there was a valve far below, one pulsating, knowing of her existence. She looked up to the head with the stars to the underside of the stallion's jaw. It spanned the size of an upside-down town. She had to get inside of him quickly, as it was safer devoured than being on him.

Closing her eyes and slowing her nerves, the mare took a deep breath, rocked left and right to the quaking of the ground, the vibrations of the monster demanding her inside. She nodded and stepped back. Then she charged forward, coming to leaping, over the edge, falling into the aperture, into the entrance of the dick.