The Curiosities of Underaged Unicorns

by Megapone

Rating: mature
Tags: Slice of Life
Length: 4814

It's a spell that every unicorn foal—colt or filly—tries at least once. After Sweetie Belle gets a hold of a spell to give herself a stallion's endowment, she, rather predictably, tries it on herself.

It's a spell that every unicorn foal—colt or filly—tries at least once. After Sweetie Belle gets a hold of a spell to give herself a stallion's endowment, she, rather predictably, tries it on herself.

Contains: Foalcon, futa, autofellatio, large endowment, self-cum inflation, messy orgasm.

A Patreon-voted story.

Published 1970-01-01 00:00:00 UTC
Last updated 2016-04-10 00:50:01 UTC

The Curiosities of Underaged Unicorns

The door clicked shut behind Sweetie Belle, the flicker around her horn vanishing just as the view of the upstairs hall disappeared. It didn't leave for long, though—as she made her way across her bedroom, small hooves padding against the carpet, her horn's aura sprang up once more, a brilliant, vibrant green twisting and dancing with an undeniable light.

Sweetie held her breath as she levitated her saddlebags off her back. Still a foal, she wasn't quite strong enough for it to be easy, but she'd been training her magic enough with Twilight that doing so was getting easier every day. Where on most days she would have tossed her bags on her bed—undoubtedly before rushing out to play with her friends—today she let them settle gently onto the hoof-knitted quilt covering her mattress. The bags, emblazoned with her Cutie Mark, sank gently into the bed.

She checked back over her shoulder, just on reflex, to make sure that the door was still closed. Her ears cocked, straining, waiting for any sound to reach them—and found nothing. Satisfied that she was alone, Sweetie let out a small breath and trotted over to her bed.

Her saddlebags sat there patiently, an oddly enticing image despite their overall lumpy appearance. Her hoof hovered over a thick, book-shaped bulge in the side, and Sweetie bit her lip. A light red blush came over her face, and she felt something twinge between her hind legs. On impulse, her eyes darted back to make sure that she was still all alone. Rarity was downstairs making dinner, and would probably be busy for a while...but it never hurt to be sure.

Still, she wasn't able to keep her hooves to herself for long. A blink of an eye later, and her horn was flickering green once more. The bag opened itself, the long, crimson red spine of a thick book coming into view as she turned the opening toward her. She floated the book out, keeping it carefully aloft as she walked it over to her little homework desk.

Technically speaking, she wasn't supposed to have this. The title on the spine said it all, really: "SPELLS OF SENSUALITY". The red of the cover itself had somehow managed to be ten times as lascivious as any other title on the entire library wall—and that, of course, had been what had caught Sweetie's eye.

Sure, so maybe Twilight wouldn't be all too happy that she'd "borrowed" this after their lesson today. She'd been sweating the whole walk home—both because of the weight at her side, and because of the lewd thoughts managing to invade her mind. Rarity would doubtlessly call them unladylike, let alone appropriate for a filly—but as far as Sweetie was concerned, she wasn't just a filly anymore.

Puberty had a way of catching up to everypony eventually, and once her attention had shifted away from her Cutie Mark, Sweetie had found herself slipping into a world that she'd scarcely known existed. More than once, she'd found herself staring at the crotch or rear of one of the other students—and averting her gaze at the slightest sound, albeit with a fairly noticeable blush. She couldn't help it. There was just something...electric in those sights that drew her gaze like a magnet. She never thought she'd be ogling Twist, of all ponies, but there was no denying that the filly had a particularly plump rear that just happened to sway with just the slightest of bounces...

Sweetie bit her lip again, an embarrassed blush tinging her cheeks. She was fantasizing again. Then again, that had been what had inspired this, hadn't it? It'd started with her staring at Button's crotch in the middle of a math lesson. She hadn't meant it, really, but the sight of his exposed sheath had left her all but shivering with a strange, alien desire. It hadn't been entirely feminine, either. At recess, she'd overheard him and Featherweight discovering some of their "experiments" behind the jungle gym, and the idea of possessing one of...those just tickled her in all of the right places.

She was curious, darn it. And the sight of one of those "erections," bobbing between Big Macintosh's legs... Sweetie's mouth went dry at the very thought. She hadn't noticed it before Twilight had left her alone with that "Everything You Wanted To Know About Pony Intercourse But Were Too Kid-Friendly To Ask" book, but afterwards... It seemed almost impossible to ignore the tell-tale signs of arousal, now. The flick of a tail. The flexing of a muscle. The slow, steady breathing as milky-white pre slowly dripped to the ground below, mixing with the mud and tinging the air with musk...

She abruptly noticed that her hoof had strayed down between her legs. Sweetie squeezed her eyes shut, and tried to force herself to turn away from masturbating. No luck. She permitted herself one stroke—and then gasped, moaning softly as her soft, filly legs twitched and tensed around her probing hoof. She was already wet, and warm, too.

Hastily wiping her hoof off on the carpet, Sweetie stood back up and turned to the book. She eyed it almost reverently as her horn lit up, the pages flickering past in a blur of motion. She'd borrowed it on a whim, really. She'd been filing away a cart of library books when this one had all but fallen into her lap, exposing its table of contents—and a particularly promising-looking spell.

She licked her lips as the spell's page finally came into view. Sweetie scanned the page, her mind beginning to tick as she took in the directions, the description, the warnings, the depictions of magic to match the flow through the horn. She double-checked the instructions, then triple-checked them. She wanted to make absolutely sure that nothing went wrong. As a unicorn, she was thankful to be capable of this spell at all, but that didn't mean that body modification magic was without its dangers. She had to be careful.

But darn it, she was too excited to be careful! She wanted—no, needed—it now! Once she was sure that she had the spell down, Sweetie nodded to herself, squeezed her eyes shut, and let her adolescent magic fill her.

Her horn flickered, sparked once—and then she cast the spell.

She waited with bated breath as the magical energies dissipated from her horn. What would happen? How would it feel? So far, she felt nothing. Sweetie's brow arched, and she swallowed as she waited for the magic to go to work. She felt rather silly, admittedly, staring down at the spellbook like this, so she took a step backward—just as a sharp, sudden heat emerged between her hind legs. Sweetie gasped, stumbling back, her hooves slipping on the floor.

One went wide underneath her belly—and brushed against something long, thick, and heavy. The weight of it threw her off balance, the sudden flare of heat making her muscles contract all at once. Sweetie gave a most undignified grunt as she plopped back onto her rear, a low thump of impact sounding through the room. Groaning softly, she rubbed at her eyes for a moment, and then slowly opened them.

What she found made her eyes grow wide in awe. Sweetie stared, her mouth hanging slightly open, at the thick, black pillar of flesh rising up before her. It started at her crotch, just between her thighs, where only moments before, a pair of delicate pussy lips had sat. It stretched up above her groin, its girthy, dark mass pushing up past her belly and nearly brushing against the top of her chest. She watched in awe as it gave a final-looking throb, lengthening until it stood at a good foot tall. It finished off with a wide, flaring head, a near-inch-wide cockslit presenting the dark, almost hypnotizing depths inside.

Sweetie felt dizzy—but elated, as well. A disbelieving smile crossed her face as she ogled the horsecock standing before her—her cock! Her stallionhood! She tensed her crotch muscles and gave a small moan of delight when she felt a tingle of pleasure run up her spine. She could see her new member flexing along with her, its essence bound inexorably to her own.

She took a deep breath, her nostrils flaring as they filled with musk. She let it enter her, felt it fill her lungs. Her preadolescent libido roared to life. Stifling a moan of lust, Sweetie struggled to peer past the girthy, mountainous shaft before her, and toward the hefty ballsack below.

Twin orbs, each the size of a good-sized grapefruit, sat nestled between her smooth, soft thighs. Her ballsack was fuzzy, her nuts perfect spheres colored a pearly, clean white. She reached down to poke one and nearly yelped, yanking her hoof back in an instant. They were so—so sensitive! It hadn't hurt, but she could still feel the reverberations of pleasure dancing through her veins, leaving her breaths long, slow, and labored.

Almost tenderly, she cradled her right testicle in the same hoof as she laid her left hoof on the shaft. Its girth seemed almost to pulse beneath her touch, almost as though it were alive. She wrapped her hoof tightly around it and found she couldn't even reach all the way around. Furthermore, the simple touch of flesh to her dark, fat member felt almost electrifying in its pleasure. Sweetie Belle groaned, a soft, foal-like whimper, as she felt her cock twitch playfully in her grasp. Touching her fillyhood had felt good before...but this was a whole new world of pleasure. Previous orgasms had always felt nice, but the mere touch of her new cock brought a feeling of solidity, of oneness, that she never could have imagined before.

The sensation of the soft, rugged carpet against her ballsack was electric, a hundred tiny bumps massaging her nuts at once. Sweetie couldn't help but moan as she felt her plump orbs groan and swell between her legs, their contents increasing in volume by the second. She could see her oversized member stir, flexing almost lazily as a fat, tablespoon-sized glob of precum slowly dripped down the side. It oozed across a particularly thick vein, which her hoof brushed across a mere second. Sweetie exhaled, and the warm mist of her breath on her flare left her head twitching with excitement. Sweetie's crotch muscles tensed involuntarily, and she gave a low groan, her soft filly's voice contrasting with the indisputable, weighty masculinity of the organ looming before her.

Tentatively, almost fearful, Sweetie Belle moved her hoof up toward the flare. It—she—was slick with precum, long milky-white strands drooling down the side. She pushed her hoof across its curve, then back down the side, her spine tingling with constant stimulation. Up and down her hoof went, her fur soft and warm against her wet, hot member, pushing and pulling in long, lazy strokes.

Her mind began to drift. Thoughts, fantasies, dreams began to stir in her mind, her mind's eye pulsing with the occasional throb of her cock. Since she'd first learned about sex, Sweetie had given into her share of fantasies about other ponies—mostly her classmates—wondering what she could do with them if given the chance. Or what they would do to her.

It was a terrible, awful, disrespectful thing to do—Rarity would tell her as much, she was sure—but she didn't care. Sweetie Belle shivered, recalling the number of times she'd imagined Rumble mounting her, his strong, jet-grey shaft pushing out from his sheath as she presented toward him, her fillyhood winking with desire. He was starting to get his stallion's growth, now; it was almost impossible to see him on a day where he didn't get an erection in the middle of class, that mottled, colt's member bobbing gently in the stale classroom air.

But Sweetie was bigger than him now—at least between her legs. She'd slipped in a few calculations during some of her sideways ogles, and had figured Rumble out to be a good seven inches long. Fair for a colt, but comparatively tiny for a stallion. His big brother, Thunderlane, she'd estimated to be nearly fifteen inches during an "accidental" bump at the Ponyville market. Though ponies always talked about how much taller, how much stronger Rumble was than Thunderlane had been at his age...

Sweetie continued to stroke her endowment, her breath misting over the top. Strands of precum stained the pure white fur of her hooves and forelegs, long, gooey ropes dripping down to pool in her lap. Sweetie felt sweat beading on her forehead as more and more of the stuff continued to pour out. Her balls were so large that she had to spread her hind legs apart to give them room. Had she been standing up or walking, they would have stuck out behind her, wobbling and smacking against her thighs with every step. She shivered with sensual delight.

It wasn't just Rumble, though. She'd fantasized about Pipsqueak once or twice, pinning him down and milking his cute, Trottingham cock as she rocked back and forth atop his belly. And yet if she was bigger than Rumble, now...who was to say that she might not let Pipsqueak be on top? She'd caught sight of his rump at recess. He was a slender colt, but his flank was pleasantly plump, swaying and bouncing playfully whenever he ran across the playground. It was positively inviting—a downright invitation to hold him close and rut him till he squealed. Her breath caught in her chest as she imagined him whimpering as she impaled him on her cock, his tiny body twisting around her colossal member as she pressed it firmly against the wall of his stomach.

Sweetie’s lower lip trembled. Her cock throbbed, and a glob of precum, thick and musky, splurted onto her cheek. She gave it a lick, on pure reflex, and actually moaned as her own hot, thick taste oozed pleasantly down her throat.

The colts weren’t the only ones she’d fantasized about, oh no. More than once, she’d have been ashamed to admit that she’d been ogling Scootaloo and Applebloom that way. Sweetie Belle just couldn’t help it—Applebloom’s hips and muscles were just so perfectly toned, and Scootaloo’s lithe, flexible form made her mouth water at the possibilities. So many nights, she’d grinded against her pillow, drool slipping down her cheek as she imagined her young, tender pusy lips pressing against Scootaloo’s, or Applebloom’s strong hooves curling around her. Now, though, she could imagine a thick, heavy weight pushing between them, pressing against their chests, thrusting against the soft fur of her friends’ coats as she grunted, moaned, came—

This time, when Sweetie Belle’s member splattered forth another fountain of pre, she opened her mouth, catching a few hefty globs on her tongue. Sweetie hummed in pleasure as she swilled it around in her mouth, feeling the droplets of warm, musky precum swishing pleasantly against her tongue. Finally, she swallowed, and felt her cock throb powerfully as her essence trickled down into her stomach, her oversized nuts already filling up for more.

Sweetie gave a soft moan, her hoof lifting from her swollen shaft to trace across her belly. She felt so empty—and her cock so full, so solid, so thick. She could still taste that little droplet of pre dancing across her tastebuds, setting them alight with salt and musk. Her heart beat a little faster in her chest as she found herself leaning forward, eyeing her flaring cockhead hungrily.

Just a little taste, she told herself. She just had to bend over a little more—at over a foot in length, and bobbing just above her chin, it was surprisingly easy to reach. And that wide, gaping cockslit, flooding with a steady stream of milky-white pre, was just so enticing. She settled her attentions there, her muzzle hovering over the pre-slick flare of her girthy shaft.

Hesitantly, she lapped at it, her tongue darting out to flick at her cockslit. Her reward was a near-instant spark of pleasure, her monstrous organ flexing away from her muzzle as shivers tingled up and down her spine. Escaping her muzzle for a moment, her shaft bobbed against her chest briefly, smearing her soft fur with a good tablespoon of pre. Sweetie caught it easily enough, though, encircling her swollen medial ring with both hooves before bringing it into place just beneath her lips once more.

She kissed the top gently, planting her lips on either side of her flare. She held the shaft still, keeping it from bucking or flexing as her groin muscles contracted with reflexive pleasure. Her tongue slowly wormed its way down her slit, tasting the warm, smooth insides of her shaft as she lapped up hefty strands of precum like a dog. Sweetie moaned, a fat droplet of pre bursting on her tongue and filling her mouth with warm, spicy flavors. She continued to lower her muzzle down, letting her endowment fill her lungs and throat as her own hypnotizing scent led her ever-onward.

The scent of her cock, masculine, salty, stifling, egged her own, drawing her attention into her shaft like a singularity of mounting pleasure. The tightness of her own gums and throat only increased the pleasure of her act; Sweetie found her cheeks growing round as she attempted to choke down another few inches of her monstrous endowment. On anypony else, it would have looked a reasonable size—yet on a filly, it was positively massive. She swished her tongue along the hot, veiny underside, and was rewarded with another splurt of precum. Sweetie felt it burst against the back of her throat and moaned softly in delight, her tiny hooves clenching as trickles of salty nectar ran down into her belly.

By now, there was a steady drool of precum oozing down her throat, a gentle river of liquid arousal that she could only eagerly gulp down. Her throat muscles contracted, hungrily pulling inch after inch of her oversized member down her esophagus in the hopes that some of this delicious substance might drip directly into her waiting belly. She kept pushing, giving a strangled "grrk!" when she felt her flare prod against the back of her throat. She needed to go further, she knew. It wanted her to go further. She had to have more.

She pushed a little bit further, sucking greedily at her cock as she might a lollipop. Her muzzle was stretched unreasonably, almost impossibly wide, her jaw creaking as each throb of her mountainous endowment forced her mouth to open a little wider. She was just so big—and yet, somehow, she was taking nearly two-thirds of the entire thing. Sweetie felt like an addict, twisting her tongue around the top half of her cock as she jerked off the lower half with her two, dainty hooves. She hoped—wanted—needed to be rewarded with more of that sweet, salty taste.

Another moan escaped her, her eyes fluttering shut as her hooves moved down to massage her soft ballsack. Her nuts had grown even larger, nearly doubling in size as they swelled with cum. Her twin orbs sloshed and groaned with seed, their enormous volumes spilling over Sweetie's lap as she sucked at her shaft with unabated lust. It tasted so good. She'd never had anything so delicious.

Sweetie inhaled deeply, feeling her monstrous orbs groaning and pushing against her hooves. They filled her grasp so well, if not too well; any more, and they'd be too large to even cup. Her mind flitted from thought to thought, her physical form occupied with pleasuring her mountainous shaft.

What would it be like to have Scootaloo sucking her off like this? Sweetie trembled with delight, her fur standing on end as she imagined stuffing this monstrous pillar of meat down her slender friend's throat. Such cute moans she'd make—and how good it'd feel.

Or little Pipsqueak, perhaps. A happy shudder went down Sweetie Belle's spine, lewd, dirty thoughts assaulting her mind as she pictured him, balanced so precariously with his hooves perched against her shaft as he suckled at it like a small foal. Goodness, but he'd scarcely be larger than her shaft was...

Sweetie's breaths began to grow labored. Her nostrils flared, her eyes squeezing shut as she continued to bob her head up and down her swelling endowment. She could feel her balls growing tighter, their stores of cum reaching a peak as her hooves stroked harder, faster at the sides of her cock. Her soft thighs pressed against her nuts, trapping them, forcing their tremendous volumes toward the base of her shaft. Rivulets of precum began to ooze past her lips, the simple rate of flow outpacing her ability to swallow it all down.

Her cock swelled, throbbing to the the rhythm of her beating heart. Sweetie Belle grunted as her jaw was pushed even further apart, each pulse of blood through her mammoth member leaving it thicker, fuller, harder. Up and down her head bobbed, her hooves roaming up and down the sides of her shaft as precum oozed past her lips.

Images, fantasies, continued to flit through her mind as the pleasure mounted. She'd pinch a filly's rump—Applebloom's, perhaps, feeling the farmer's tight, muscular flank. Another splurt of pre burst against the back of her throat, Sweetie's thoughts filling with potential sensations. She'd hold Applebloom's head tenderly in place, shoving her length down the other filly's throat as her load exploded down Bloom's throat. On and on she'd cum, her orgasm leaving the both of them panting, moaning, groaning for more.

Sweat dripped down Sweetie's cheeks and forehead, her filly-pitched grunts of pleasure reaching a fevered crescendo. She twisted her head, vainly, helplessly trying to swallow even more of her cock. She wasn't sure what it was, but she was getting closer to...something. It was an alien feeling, a tightness lodged deep into her groin, completely different from the powerful ebb and flow of the orgasms she'd experienced before. She could feel her whole body, her mind, her entire sense of self tightening and focusing at the base of her shaft, her mind blanking as she came ever-closer to falling off the edge.

Her hips bucked, and Sweetie's eyes rolled back in her head. She was so close now. Her thighs flexed, her cock throbbing as it swelled another inch, lodging itself even further back in her throat. She could nearly choke on that length, so hot, so wet, so thick. The pressure was undeniable now, a swelling, mounting tide that even the strongest of dams couldn't possibly hold back—

There was a knock on the door. A voice, musical, sweet, and undeniably Rarity, slipped through the crack. "Sweetie Belle?" Rarity called, rapping again at her bedroom door. "May I come in?"

Sweetie's eyes opened wide. Rarity—but—

There was no time! Her cock was too firmly stuck in her throat—and then she was past the point of no return, her cock pulsing and throbbing as she felt herself go over the edge.

The door clicked open, Rarity's form becoming visible just as Sweetie's eyes squeezed shut. "It's time for dinner—" Rarity began.

And then Sweetie's orgasm began.

A huge load of cum—monstrous, thick, gooey, and hot—flooded down her throat. Sweetie choked around it, gargling with a mixture of pleasure and fullness as she felt it rush down to fill her stomach. Her overfilled balls churned, outputting more and more jizz by the second as she felt an absolute sense of release pulse in her veins. As her nuts seized up, their enormous volumes groaning with density, she could actually feel them pushing her load up the shaft as it bulged even wider, her jaw creaking audibly as she struggled to swallow it all.

On and on it came, Sweetie losing herself in the throes of orgasm as the neverending tide of seed filled her with every pulse of her organ. She gulped down her seed greedily, eagerly swallowing mouthful after mouthful of her own warm, fertile load. There was just so much of it—and it tasted even better than her pre had! She moaned, happily guzzling each fresh volley of seed as she launched cupful after cupful of jizz down into her stomach.

Extra cum, too much for a little filly to swallow on her own, dribbled past her lips. It matted her chest fur, making her coat sticky and wet, as strands of spunk oozed across her belly. Sweetie felt her eyes roll back even further as an ambrosia of pure pleasure filled her. She continued to milk her own cock, using both hooves and grunting loudly as cupfuls of sperm came cascading down her throat.

She could feel her belly tightening, swelling, rounding out with each new load of spunk that she swallowed. Sweetie gurgled, groans and grunts mixing with simple, childish moans of delight as she felt her belly grow larger, almost looking pregnant from the sheer volume of her load. Her hoof found her gut and began to stroke it, even as her other foreleg wrapped hungrily around her spasming cock in an attempt to spill even more of its delicious seed.

Finally, her output slowed to a trickle. The production of even her balls couldn't last forever, and so Sweetie found herself panting, her chest heaving, as her cock popped wetly out of her mouth. She groaned, rubbing her swollen gut with both hooves as her softening cock dragged against her chest, leaving fat smears of precum in its wake.

She felt so exhausted—and yet so satisfied. The afterglow was like nothing she'd ever felt with her marehood. It filled her completely, a bone-deep sense of oneness that set her mind drifting across a peaceful sea of warmth and pleasure.

At the sight of the shadow in the door, though, she struggled past it. Sweetie gaped at her sister, noting Rarity's wide eyes. "Rarity!" she blurted. Sweetie faltered, then tried to hug her member to her chest. "I—I can explain!" She did her best to hide her new genitalia, and only afterwards realized how remarkably ineffectual it was for a tiny filly to attempt to conceal a foot-long stallion, especially after coating herself with cum. She tensed up, paling as she prepared for what was to come. Would Rarity explode? Scold her? Gasp—or faint?

And then Rarity laughed.

Sweetie's eyes widened to the size of saucers, but Rarity had already stepped inside, giggling like a schoolfilly.

"Well," Rarity said dryly, smirking down at her. "That certainly doesn't look like homework."

"Um," Sweetie said. There was something here that she wasn't quite getting, and the thought made her head hurt. She felt a long strand of cum drip down her cheek, and quickly slurped it back up.

Rarity's eyes darted down to the package between her little sister's legs. "That's quite a well-formed stallionhood you have there," she said, an unmistakable note of amusement in her voice. "Quite a bit nicer than my own, I'd say. You always were the better with magic."

Sweetie's train of thought came to a screeching, squealing halt.

"You—you what?" She had to make an effort not to babble. "But you—how—"

"Oh, Sweetie." Rarity looked about ready to burst into laughter. "Every unicorn experiments with this manner of magic eventually. The mares want one, the stallions want a bigger one." She shrugged, her horn sparking with magic as her smile twitched. "Honestly, it's quite understandable."

Sweetie just nodded along. She felt it was the safest response. Something in her mind wasn't quite willing to work.

"You did a fine job, too," Rarity said. Sweetie wasn't entirely sure how to feel about that compliment. Rarity turned to smile at her, her eyes half-lidded. "Though mine was bigger. Thunderlane certainly wouldn't stop blushing at it."

Sweetie had a huge blush of her own on. "Rarity!" she squeaked. "You shouldn't—I mean, you shouldn't be telling me this!"

"Nonsense." Rarity smirked. "Now, as I said, dinner is ready." She eyed Sweetie's pregnant-looking belly for a moment, her smile twitching. "I saw the size of that orgasm, though. I'm not mad at you for using that spell, but if you've spoiled your appetite, I shall be quite upset. I made lasagna."

"Lasagna," Sweetie mumbled. "Right." She glanced down at the space between her legs, and noticed with a flush that she was already starting to get hard again. She looked back up, and met Rarity's gaze. Her older sister smiled, raising an eyebrow.

"It looked like you were quite enjoying the taste," she said. She turned to go, and twisted back to say, over her shoulder, "If it's that good, I might have to sample it myself."

Sweetie gaped after her, her jaw hanging open wide as Rarity trotted off downstairs, laughing all the way. Red-faced, her cheeks hot, she felt at a complete loss for words—save for one.

"Rarity!"