Estrus among us

Rainbow saw her opportunity as the other townsponies were being overcome with orgasms, and Twilight was distracted. It took every ounce of her willpower not to join into the pile, as she'd only experienced a little taste of Alex's magic from his hands at the party the day before, but as she zipped behind the house she could still hear Big Mac pounding Fluttershy into the bed upstairs, and her maddening cries of pleasure!

That mental image made up her pegasus mind!

Contrary to most residents' opinions of her (and possibly, a few of her friends) Dash wasn't stupid. She was simply...single-minded. Once she fixated on a goal, she poured every ounce of her strength and will into achieving said goal, and sometimes obstacles like "common sense", "safety", or "careful-thought-beforehoof" be damned! Those things would just slow her down, and she could be slow when she was old!

And probably, not even then.

In the midst of her envy of Fluttershy, she had not failed to notice the size of her new wings, and how big her Human breasts were, indicating much larger chest muscles. Guessing her friend's new weight to be around ninety-five to ninety-eight pounds and her new wingspan to be at least six feet, she did the quick calculations of mass/wing ratio in her head to determine her wing lift was now significantly greater. Throw in her pegasus magic which Dash assumed she still had, and the results were...frustrating, to say the least.

In short, Fluttershy could now fly rings around her. FLUTTERSHY!

This? Was intolerable!!

So, besides the great sex she was missing out on, there was the possibility she could have wings like that! Sure, she remembered Applejack's warning, but she'd always been a gambler, and 50/50 odds were good in her book! Also, there were at least four other mares about to fuck Alex, and Celestia only knows how long that would take! She knew from personal experience the Human stud had phenomenal sexual stamina, but even he must have to rest after satisfying four horny mares! And who's to say it wouldn't be days before she had her turn, especially if that greedy slut Rarity caught wind of what was going on?! And don't get her started on Pinkie "Balls Drainer" Pie...she'd seen that slut take on five stallions at a party once, sucking each of them dry one after the other until they'd passed out! And she still kept going! Over the years, she'd come to dearly love Pinkie, but Sweet Celestia that mare was insatiable! Even Derpy couldn't keep up with her!

Derpy!

So, her mind was made up. Peeking her head around the corner once more to make sure the coast was clear, she flew up to the window and looked inside. They were both lying in each others' arms, seemingly passed out in post-coital bliss. The bed looked like it was off its frame, and she could see a huge dent in the far wall. "Good lord...what kind of sex were they having up here?" Slowly, she eaaased the window open and crawled inside. Mac was on his back, with Fluttershy snuggled up alongside him, both of them looking like they had just passed out. Dash licked her lips as she focused on the prize: that tasty-looking, huge log of stallion meat! His scent filled the air, even with the window open, and it was all she could do not to jump him right then and there! But even in her aroused state, she knew he might not be quite...open...to her advances, so she slowly crawled up on his other side and licked his ear.

Mac smiled, took a deep breath, and stretched. "Mmm...Fluttershy...I need a minute, gal...y'all done almost worn me out..."

Dash whispered, "I'm not Fluttershy, stud..." then kissed his ear again. Mac's eyes flew wide open, and he shifted his head over to her.

"R...Rainbow?! Whut...whut are you doin' here?!" he said back quietly, so as not to wake the ponygirl.

She stared at him with bedroom eyes. "...take a wild guess, farmboy..." while caressing his chest. He spared a glance over at Fluttershy to make sure she was still asleep, then turned back to the horny mare.

"I...I cain't! Y'all heard whut AJ said; y'all could end up a monster, or sumthin'!" But she trailed a hoof slowly down his chest, over his stomach, then finally over his cock, and began lightly stroking it.

"Why don't you let me worry about that, honey..." Under her gentle attentions, and despite his protests, he began to stiffen. Still, he wasn't quite ready to give up just yet.

"Rainbow, I---" but she cut him off with a sultry kiss, as he grew to full mast, hard and throbbing.

Keeping her half-lidded gaze on him, she then licked the baby-soft part under her hoof, then kept stroking him as she throatily whispered, "I'm gonna put your long...hard...delicious cock into my hawwt, wet mouth...and then I'm gonna suuuuck it...until you cummmm down my throat...and then..." as she gave him another hot kiss, "I'm gonna swallow every...last...drop...of your," she leaned forward to whisper in his ear, "...cum..." She smiled as she felt his dick pulse under her hoof, then licked behind his ear, trailed kisses down his throat and chest, making him moan, then finally reached her huge, meaty prize. Giving him a half-lidded stare to watch his reaction, she grasped his schlong in both hooves and took her sweet...ass...time bringing her hot mouth over it...then engulfed him in one quick motion. He jerked and bucked his hips, sending a quarter of his length into her wet, tight throat, which almost made her cum right then and there! She then closed her eyes and fell into a rhythm of bobbing her head up and down, savoring every mouthful of cock as it plunged deeper and deeper into her mouth and willing throat.

He never stood a chance.

Soon, her spit coated and flowed down his cock, as she took in more and more of it, determined to enjoy as much of this beast as she could! Her eyes rolled up in her head as his dick kept hitting the erogenous zone in the back of her throat, and her first climax hit her without warning! She moaned around his meat but kept going as she bucked and spasmed her hips, now able to swallow half his length into her throat and back...up and down...in and out...wings unfurled and her breath heaving in waves!

Mac's eyes grew even wider as he watched her reaction, which cranked his libido up to the breaking point! He took his left hand and grabbed her head, then growled, "So...you want dick?! Then," he grunted as he thrust his hips upward, "here it comes!!" He closed his eyes and opened his mouth as he unleashed a torrent of hot, creamy spunk into Rainbow's mouth and throat, grunting each time he thrust again and again, over and over, giving her no time to recover from each deluge! It was all she could do to swallow frantically as her stomach quickly filled with his hot cum. She mewled helplessly but couldn't escape, not with his powerful hand holding her head down over his cock, and it buried in her throat! All the while she was also cumming herself again, as her vision flashed and she waned in and out of consciousness.

Finally spent, he sighed and released her, flopping his hand down onto what was left of the destroyed mattress. With his cock still in her throat, she blinked, then set her hooves on his thigh and slowly pulled upwards, sliding him out of her throat with a wet >shrlop!< then fell panting onto his thigh with her face on his still erect cock.

As she caught her breath, she looked over at Fluttershy and said, "I...I...thought for...sure we...woke her up!"

Mac looked over at the still-sleeping girl, smiled, and turned back to Rainbow. "I think I done worn her out. She ain't gonna wake up anytime soon!"

Weary, but still determined, Dash dragged herself up, crawled on top of his dick, and positioned her pussy over it. "Good..." she panted, "...because I'm not even halfway done with you!"

But just as she'd closed her eyes and eaaased herself down on his cock with a smile and a sigh, he reached up and grabbed her by the hips. Her eyes flew open in surprise as he climbed to his feet and off the bed, with her still impaled on his dick. He stood to his full height, spread his legs, and leered down at her still gripping her tightly, while she stared back up at him with shrunken pupils. "N...now...hang on...Mac..." she began, as she looked down between her spread legs and the...intimidating length of cock that awaited her, "...let's take it easy..."

Mac started to slooowly thrust into her, going deeper every time. "Isn't...uhhh...this...what...uhhh...yer so tight!...you...wanted?"

But the single-minded mare was rapidly losing control of that mind. "Buh...buh...buh...but...I...I...wan...wanted...to...so deep!...ri...ride...you!" Her eyes rolled back in her head once more as he sped up his thrusts. "Bi...big...DICK...BIG...DICK...!"

Mac grit his teeth and began to unleash the full power of his cock on the diminutive mare. "That's RIGHT! An'...now...huh...huh..huh...yer...gonna...GIT IT ALL!!" His hips became a blur as he fucked her with complete abandon, as she in turn bucked her hips and squirted, having LONG lost count of how many times she'd climaxed! All she could do now was endure her sexy punishment, being held in place only by his hands on her hips and his dick in her hot, slick cunt.

Just as everything was going black, he stopped and pulled out of her. She wearily raised her head and whispered, "Is...is it...over?" But instead of answering, he turned back to the bed, threw her face down on it, fell to his knees behind her, and pulled her tail up. It took a moment for her sex-fogged brain to register what was going on, but when it did her eyes flew open wide again. He held her with her face in the mattress and her ass in the air, so she struggled to look back at him. "Big Mac! No! You'll never fit...not in...there!"

But he easily held her still with one hand while he used the other to line his cock up with her ponut. "I gots a confession to make, Rainbow," he said as he slowly began to push forward, "I...uhhh...always...wanted...to...uhhh...fuck you...in...yer...ass!" She gasped as the head, still slick with her own juices, penetrated her asshole and just...kept...going! This time though, the stallion remained gentle, knowing he could seriously hurt her if he lost control. So he maintained a steady rhythm and didn't give her more than half his dick...at least...that was the plan.

Until Dash screamed, "MORE!!" Mac paused in shock, and she looked back at him in fury! "I said MORE, damn you!!"

"Bu...but...I don't wanna hur---" and that's when Fluttershy gave an exasperated sigh, sat up, and glared at the two of them.

"Would. You. PLEASE fuck her in the ass as hard as she wants?! She can take it!"

Mac and Dash stared at her. "How...long have you been---" he began, but she cut him off again.

"Oh, for Celestia's sake! Here, let me help!" She got up, went behind Mac, grabbed his ass, and began shoving him into her friend's ass! Dash shrieked and stuck her tongue out as she arched her back and spread her legs even further.

"That's what I'm tal...talkin'...Ah! Ah! Ah!...about! Woo HOO!!" while her ass rippled and bounced with each mighty thrust. Mac soon took over as the pleasure of fucking her tight ass radiated all over his dick and reached his brain, so Fluttershy took his face and turned it to hers, then locked her mouth on his and began to wrestle his tongue.

Mac's eyes became lidded as his climax approached, which did not go unnoticed by the horny ponygirl. In his ear, she whispered, "Fill her ass for me, Mac...then, it's MY turn again...!"

Mac stuck his tongue out and nodded, never slowing his jackhammering of his fantasy lay's ass. He looked down at her, watching his cock slide in and out of her ponut, and growled, "Yeah! Yeah! I'm...gonna...GIVE...it...to...YOU!" He grunted a few more times, then buried his cock as far as it could go! "I...I'm...cummmmin'...!"

Rainbow shut her eyes and grit her teeth. "Yes! Sweet Celestia, YES! FILL ME!!" She threw her head back and shrieked again as she felt his hot, thick spunk UNLOAD inside her ass, over and over and over...until it overflowed and spilled down her legs and onto the already ruined bed. She fell forward, panting, as he took a few moments to catch his breath, then sloooowly pull his cock free from her tight ass.

She was just raising her head to look back and thank him for a job well fucked when she stopped.

And looked down at herself.

And realized she was glowing.

She had just enough time to ask them, "Hey...what's going---" before she was surrounded by a cloud of bright light! Mac and Fluttershy stood back and shielded their eyes. They could no longer see her, but they could hear her writhing, convulsing, and crying out, "Why?! Why does it HURRRT?!"

Then there was another puff of smoke, and the bright light dissipated. The other two brought their hands away from their eyes and cautiously stepped forward, waving away the smoke so they could see. "Rainbow...are you alright?" asked Fluttershy. When they finally saw what she'd become, they both gasped.

Rainbow was lying on her side, so she slowly pulled herself up and looked at them. She now had Human breasts, which were also now gigantic, and she raised her Human arms to look at her Human hands. But she had grown no larger, she was still the same size she was before, and she still had pony hooves instead of feet and her pony tail.

She'd been turned into a half-pony, half-Human.