“Okay, so, important stuff first. She ain't gonna die, right, doc?”

Doctor Horse nodded, and Carrot Top continued; “And it's not, like, anything serious. No terrible magical disease or disorder or some other weird unicorn thing that's going to make Dinky's life miserable forever?”

“No, she'll be fine. Just have to deal with an extra appendage for a while.”

“How long is a while? Because Derpy'll fuckin' kill me if it's anything important.”

“It isn't, I assure you, Mrs Hooves.”

Top frowned while Dinky awkwardly twiddled her thumbs, sitting on the exam table. She was currently only wearing a hospital smock, naturally one size too small, with a conspicuous tent in the groin area. She looked down, blushing. “You're absolutely sure, then? It's going to go away eventually?” He nodded again. “Okay, then, when? Gimme a fuckin' timeframe to work with.”

“Ah, yes. Unfortunately that isn't something I can do.”

“Why the fuck not?”

“That would have to do with the nature of what exactly happened to Dinky.” He handed Carrot Top some papers. “The short answer is that it's a 'weird unicorn thing.' The long answer is that it has to do with puberty. As you know, ponies of different tribes have different things happen to them in addition to the standard growth and development of secondary sexual characteristics. Mostly to do with their particular tribe's magic. What's happening is... somewhat complex. Far too complex to really warrant going into detail, especially since you've almost certainly learned this yourself.”

Top shrugged. “Back in, like, middle school. I don't see what this has to do with Dinky growing a cock all of a sudden.”

“Well, a simplified version is that every pony has his or her own reservoir of magic, that's channelled in different ways depending on the tribe. Earth Ponies get enhanced physical strength and endurance, Pegasi get flight and weather manipulation, Unicorns get magic. Here, take a look at this diagram.” He put a finger on the paper he'd handed to Top. “As they go through puberty, a Unicorn's magic channels develop and grow. Think of it like baby teeth versus adult teeth. And, much like teeth growing in, it can result in some... growing pains.”

“Like the cock?”

“Yes, actually. In infancy, and then later near the end of puberty, Unicorn magical channels expand, which leaves the young Unicorn with sudden access to a much greater flow of magic, which can result in them randomly casting very powerful spells with or without meaning to, often more powerful than they will ever be capable of casting for a very long time or even ever again. It isn't entirely random, but triggers can be unpredictable. In Dinky's case, having her first real sexual experience was an intense enough experience that it triggered a miscast that resulted in, well.” He coughed, pointedly not looking at the dark spot that was spreading on Dinky's smock. “Anyway, the point is that unfortunately, without running further tests, we can't determine exactly what it was that Dinky's magic did. Tests that Ponyville General Hospital doesn't actually have the equipment to conduct. Short of sending her to a specialist in Canterlot, which would be... not cheap at all, there's not much we can do for her for now.”

“You're sure? There's nothing y'all can do?”

“We could forcibly terminate the spell, but doing so without knowing what it actually is could lead to serious negative developmental effects for Dinky.”

“How negative are we talking?”

“Completely burning out her magic channels leaving her incapable of Unicorn Magic short of getting a prosthetic horn. Which would be even more expensive than sending her to a specialist.”

Carrot Top winced. “Okay, yeah, let's not do that.”

Doctor Horse nodded. “Fortunately, there is one thing I can say for certain. Whatever spell Dinky subconsciously cast on herself, it very likely isn't permanent. The penis isn't illusory, and is fully functional. Physically, she is functionally both male and female. That kind of transformational spell would already be fairly advanced. For it to be permanent would require either her to have a special talent conductive to permanent physical alteration magic, or an alicorn magical reservoir capacity – in layman's terms, Dinky would either need to specialize in alteration magic or have access to nearly twenty billion times the magical energy that she does now in order to brute force it.”

“Okay.” Carrot Top nodded. “So all we can do is wait, then?”

“Yes, unfortunately. I'll see what I can do, but there's a very real chance it will go away on its own in the meantime. For now I'd recommend having her take some time off of school. She needs to get used to having a penis, and there's the very real possibility that another misfire could occur. Limiting her exposure to other ponies will hopefully help lower that risk.”

Dinky frowned downwards. “Come on, you stupid thing. Go down so I can get dressed.” Her cock, achingly hard, merely twitched in response, a bead of precum forming on the urethra. “Fuck.” She flopped backwards onto her bed, trying very hard not to cry. “I'm not gonna give you the satisfaction of jerking off you stupid... fuck.” Her mother had lent her some of her underwear – enchanted to hide her own extra appendage – to wear so she could be around other ponies without sporting an obvious bulge that hadn't been there before.

Unfortunately, the magic didn't work unless you first got the panties on. Which was proving difficult, between the raging erection that refused to go down no matter how hard she thought unsexy thoughts, and the fact that her mother's hips were significantly wider than her own. “Come on, school's already over and Miss Cheerilee would have sent someone over with my homework and notes and shit. I need to get dressed before they get here, which I can't do if you don't fucking go soft already for fuck's sake.”

It twitched again. Dinky grunted, partially out of frustration, but mostly because it felt so damn good. She buried her face in her hands (mostly to give them something to do other than slowly drifting to her crotch) and groaned. “They'll be here any minute! Just go down you've been hard all day and I haven't seen anything sexy at all!” Strictly speaking, the last time she'd seen anything she'd consider sexy, she'd grown a cock.

“Fuck it, I don't have time for this.” Even if she were to masturbate, it was doubtful she'd even cum before whoever Cheerilee sent arrived. She pushed herself upright, slumping over and blearily scanning the floor of her room. Usually it was much neater than this, but she'd been getting lazy about using the laundry hamper. And the thing had been keeping her awake at night, the painful arousal too much for her mind to be able to relax. There, in the far corner, was the only pair of pants she'd worn for the past few days – grey, tatty sweatpants that had once belonged to Carrot Top. They had been slightly baggy on Top, but on Dinky it was like wearing a circus tent. There was no way that her cock was big enough to produce a noticeable bulge while she was wearing those. Dinky put a hand on either side of her body, lowering her torso slightly before pushing...

“Hey, Dinky! Mith Cheerilee thent me with todayth noteth and homework!”

... but before she could so much as get off of her bed, the third worst possible pony Cheerilee could have chosen barged into her room.

“Oh, hey, you're a futa? You should have thaid thomething thooner, maybe we could have had thome fun!”

“Graaaaagh!” Dinky flopped backwards onto her bed again, not even bothering to scramble to hide her new stallionhood. It was too late. Twist had already seen it. Of course the pony who brought her her classwork for the day would be the biggest slut in school. “I don't suppose I could convince you to just put it on my desk and leave?”

“Dependth on how contagiouth you are.”

“Ugh.”

Twist smiled warmly, sitting down on Dinky's bed next to her. “I'll take that ath a 'not contagiouth at all.' It'th been almotht a week thinth we've talked, Dinky! I wanna know how you're doing!”

It wasn't that Dinky disliked Twist. Parsing her lisp could be a pain, but it just took a few moments to get used to before you started to mentally filter it out. And aside from that, there was very little about her not to like. In fact, Dinky mused as she pushed herself into a sitting position once again, Twist was probably one of her closest friends. Normally she wouldn't have any problems with getting to quickly catch up on the latest gossip, but in this situation, Twist was decidedly not someone she wanted to see for several obvious reasons. She glanced sideways, taking in the reasons. They were large, half again the size of her head, perfectly firm. Twist claimed they were the result of a glandular condition combined with a very generous puberty, but Dinky wasn't entirely sure they weren't the result of cosmetic surgery. Or possibly cosmetic sorcery. Either way, the only reason that Twist's enormous breasts were credible to Dinky was that Top's were bigger, and she knew they were natural.

Throughout elementary school and into high school, Twist had been short and scrawny. The only attention she ever really got, aside from her two or three friends, was from Diamond Tiara and Silver Spoon making the occasional snide comment. And then one September she showed up on the first day of school completely transformed. She wore the same outfit she always wore – a plain white t-shirt coupled with denim overalls – but suddenly she was a good two feet taller, and the shirt barely covered the top third of her gigantic tits, let alone her nipples. Combined with the also-much-too-small-for-her overalls, and she might as well have not been wearing anything. She had been sent home, of course, and had come back the next day with slightly less revealing clothing, but the damage had been done. Twist had gotten a taste of the positive attention that her new assets brought and discovered it to be to her liking. She didn't own a single outfit that didn't show off a good amount of fur, as far as Dinky was aware. And she had absolutely revelled in the attention her breasts brought to her. In all of its forms.

She took pride in having sucked every single cock, male or female, that she was aware of in Ponyville High within the first month of tenth grade.

“Hm.” She reached down and gave Dinky's cock a firm squeeze, eliciting a shocked gasp. “Decent girth. Decent length. For a stallion. I don't wanna be mean, but you're really small for a futa.” She strengthened her grip and gave the cock a good, solid pump. “I mean, Silver's got the smallest futa cock I've sucked and even she's just under two feet hard.” She reached over with her free hand and scooped up some of the copious flow of pre Dinky was leaking. “Production's nice, at least. Nowhere near as much as Miss Cheerilee, but her cock's as big as I am so that's not really a fair comparison. Still, let's see about taste.” She brought the precum to her face and gave it a lick. Her eyes widened slightly behind the thick, purple rims of her glasses, and she dove in, greedily lapping up the small pool of cum before licking her hand entirely clean. “Holy shit, that's good! I've never tasted futa cum so fuckin' manly, and that's just pre!” With the practised motions of an expert, Twist moved from beside Dinky to on the floor in front of her, not once pausing her handjob. She brought her face in close, her hot breath sending aches of arousal through Dinky's body. Pale golden sparks shot out of her horn in time with the pulses of heat travelling up and down her spine. “Mmmm, hurry up'n cum so I can get a taste of the real thing.” Without another word, Twist took the cock into her mouth, up to the hilt in one motion.

Dinky's body tensed, and she came. Hard. Harder than the first time she had came, her hips thrusting powerfully into Twist's mouth on their own, like she was attempting to force more of her cock into the hot embrace of Twist's tight throat. Instinctively, she reached down and grabbed two handfuls of curly red mane, to more effectively fuck Twist's face. Gout after gout of hot seed spurted from her cock, far more than her walnut sized balls really should have been capable of producing.

After what felt like hours but was more like half a minute, Dinky felt her orgasm begin to lose momentum. Slowly, inch after agonizing inch, Twist pulled her head back, the sensation drawing Dinky's climax out and out, along with Dinky's cock. All ten inches of it, and then more. Twist reached up, giving her now plum-sized balls a squeeze with one hand, and grasping the base of her cock with the other, gently pumping it as a grin spread across her face – she could no longer fully close her hand around its girth. Eventually, the head popped out of Twist's mouth, splattering two last gouts of cum across Twist's face. She let go of it, and its now fifteen inch length, still rock hard, slapped against Dinky's chest, staining her fur with the dregs of orgasm.

“Delicious.”

“Holy shit!” Dinky shouted between the heavy pants of afterglow. “What the fuck?!”

“Your cock grew,” Twist replied matter-of-factly. “About five inches, I'd say.” She rolled her eyes at Dinky's panic. “You're acting like that's weird. Most stallions I've done do the same thing. Hell, Pip's cock goes from five inches to three feet when he cums.” She licked her lips wistfully, catching a bit of Dinky's cumshot. “Mmmm, he's a bit of an extreme example though. Five inches is much more normal.”

“So... it's supposed to do this?”

“Prolly. And hey, now you're big enough for a proper titfuck!”

Dinky blushed. “Twist, I don't know. This feels weird.”

“Hey, relax. It's all good fun. Hey, wanna see something cool?”

Before Dinky could either object or consent to seeing something cool, whatever that might be, Twist leaned back, spreading her legs. She rested on one hand, the other moving forward and gently rubbing the soft swell of her pussy, clearly visible under her thong. “See, a lotta folks don't know a lot about Earth Pony magic. You get strong, you get tough, that's about it. But, see, waaay back in tenth grade when these babies happened, I looked it up and there's more to it. And it turns out that yeah, there's more to it. Like, you know how all of the Apples are built to hell and back? That's an Earth Pony magic thing, too. And, like, Earth Pony families are always huge? Same thing. Turns out Earth Pony magic is all about fertility. That's why we're so good at farming and shit. Which basically means that, once you know what you're doing, you can do stuff like this!”

There was a creaking sound, and then a snapping sound. “There goes the bra. Normally I don't do this with a shirt on, but it's more impressive this way. You might wanna duck, by the way.”

“Wha-” Dinky quickly dove to the floor, leaving her face-to-barely-covered-by-her-thong-pussy with Twist as the buttons on her top, a sleeveless midriff-baring affair popped its first button. One by one, the already straining buttons snapped, until her shirt burst open, unleashing her breasts from their cloth prison onto the world and Dinky.

“I mean, it's not much growth. Just about enough to bust a bra and a shirt. But once I get good at it, I'll be able to make these puppies bigger than me!”

“What.”

Twist grinned. “The point is that you're not the only one with weird stuff going on, Dinky. Just relax and lemme give you a nice titfuck.”

Dinky groaned in exasperation. “Twist, look, I'm not... supposed to be doing this kind of thing until the doctors figure out where this thing came from, and now it's bigger and it's still hard and this is clearly not normal, despite whatever you've got to say about Pip and your boobs and whatever.” She pushed herself into a standing position. “Look, just... put my homework on my desk and- I don't know, okay, this feels weird and wrong and-” She found her eyes insistently darting their way back to Twist's bare breasts, each now twice the size of her head. Her nipples, erect and swollen, leaked a steady stream of sweet-smelling translucent fluid. “... Are you sure I'm big enough to, you know? I mean like your, um, your breasts are pretty big and, um.” Dinky blushed.

“You're cute when you're flustered.” Twist got up. “Look, even if you're not quite big enough for a proper titfuck, we can still have a little fun. Just sit down on the bed and we'll get going. Don't worry, I'll take the lead, you just have to sit back and enjoy yourself. If I tell you to do something, do it, otherwise just relax. You're to tense!”

Dinky, awkwardly blushing, sat down on her bed once more. Twist approached her, getting down on her knees. “A titfuck's pretty simple. Hup!” She hefted her breasts and plopped them onto Dinky's lap. Their sheer size meant that they more than filled the available space, spilling onto Dinky's bed. She gasped as suddenly her cock was surrounded by soft, warm titflesh. “Grab my boobs, Dinky.” Awkwardly, Dinky manoeuvred her hands to either side of Twist's tits.

Twist gently took her hands in her own, and pressed them inwards. The sudden increase in pressure drew another gasp from Dinky. “Ohfuck.”

Twist grinned. “Yeah, normally if my tits were smaller or if your cock was bigger, I'd be able to give you oral as well, but honestly? Turning my tits into a makeshift cunt is way fuckin' hotter.” She pressed Dinky's hands into her flesh more forcefully, and began to move them up and down. Slowly at first, but quickly picking up in intensity.

“Ohfuck,” Dinky grunted, her voice strained. Her mind swam with confused arousal. This was wrong. Twist was her friend, and yet here she was, mindlessly fucking her like an animal. Her horn began to sputter again as she groaned. She'd never looked at Twist as anything other than a friend before, but now...

She looked down at Twist. Now she was a pair of giant tits giving her a titfuck and fuck it felt so damn good. “Ohfuckohfuckohfuck gonna get biggerrrrrrrrrrrr!” Her horn sparked, an explosion of golden sparks raining down as she came. And then came again.

And again.

And again.

And with each orgasm, her cock pulsed larger. Cum splattered all over her thrusting hips from the gap where her cock entered the tight embrace of Twist's tits, and all over the ceiling as her cockhead quickly erupted from their embrace, much to the surprise of Twist. Cum erupted in a constant flow as orgasm after orgasm wracked Dinky's body.

“Holy shit.” Twist stared in awe as Dinky's cock reached twenty inches, its growth stopping long before her orgasm showed any signs of slowing down. Just the sight of so much cum was enough to bring her to her own climax, and she instinctively clamped her mouth down over the gusher of semen, swallowing as much as she was physically capable of. Cum spurted from her nose in thick gouts, and her tits let out their own gysers of fluid as the flow of milk redoubled itself. Her belly felt heavy with the sheer amount of spunk getting pumped into her, and there was absolutely no sign of it slowing down. She coughed and sputtered and eventually fell backwards, landing on her back as Dinky continued to cum and cum and cum. Twist stared in awe – the only pony she'd ever encountered who came even close to that level of production was Miss Cheerilee, who was a special case. Dinky's orgasms continued for a further ten minutes before she finally came down, collapsing backwards onto her bed, dripping with cum that had drooled down from the ceiling of her room onto her.

It took a moment for Twist to regain her composure. Slowly, she pulled herself to her feet, her belly sloshing with its load of cum. “Wow. Wish you'd told me you could do this sooner 'cos that was fuckin' hot.” She rubbed her belly, gravid with Dinky's seed. “Fuck, I look pregnant!” A crazed grin slowly spread across her face. “Look, Dinky, I've... I'll be back, but I've gotta go somewhere real quick. Trust me, you're gonna love this!” With that, she turned and ran, still topless, out of Dinky's room and, presumably, her home.

Still in a daze, all Dinky could do was mutter, “Wait. What about my notes?”

And then she passed out again.

Author's Note

Second chapter! This one was fun to write. Even managed to sneak some cumflation in there. Speaking of, headcanon; ponies are stretchier than humans. Better for cumflation, you see.

I am so so very sorry for transcribing Twist's lisp, even if only for a few lines.