Diamonds in the Buff

by Megapone

Rating: mature
Tags: Slice of Life, Anthro
Length: 5533

Rainbow Dash takes Rarity to the gym. Unknown to her, Rarity puts on muscle mass and size a bit more quickly than most other gym-goers. Rainbow Dash is about to find this out.

Rainbow Dash takes Rarity to the gym. Unknown to her, Rarity puts on muscle mass and size a bit more quickly than most other gym-goers. Rainbow Dash is about to find this out.

Contains: Muscle growth, regular growth, mini-macro/giantess/amazon, size difference, size shaming/comparison, clothesbursting

A commission for Unideal

Published 1970-01-01 00:00:00 UTC
Last updated 2015-07-16 02:40:02 UTC

Diamonds in the Buff

"C'mon, Rares! They're about to open!"

"Are you sure about this, Rainbow Dash?" Rarity blinked up at the large, imposing Ponyville Gym with more than a hint of skepticism in her eyes. "It's rather early for a, ah, workout, did you call it?"

"Come on," Dash said. She tugged on Rarity's arm, her wings fluttering impatiently behind her. "I wanna be first on the treadmills. And it's not early at all. Everypony's waiting for them to open!"

Rarity eyed the assembly of large, sweaty, musclebound stallions with an equal mixture of apprehension and interest. Apprehension because—well, they were sweaty, and more often than not far too hairy. But she had to admit that the bulging biceps and chest she noted on one particular tall green-furred stallion were quite appealing.

"Oh, very well," she huffed. "I don't want to try anything too rough, though. I might break a nail."

Rainbow Dash scoffed. "Please. You gotta get rough at the gym, Rarity. Or at least work hard at it." She grinned and flexed her  right arm, her left hand squeezing her bicep. "How else are you gonna get buff like me?"

'I don't want to get 'buff'," Rarity said. "I just want to be a little more in-shape, is all."

"Fine, whatever." Rainbow Dash rolled her eyes. "You've gotta take this at least a little bit seriously. Who spends two hours straightening their hair before going to the gym?"

"A mare who takes pride in her appearance," Rarity said, "and I'll not have you forget it. I refuse to get it all sweaty and messy and dirty, unlike some of these"—she shuddered—"unkempt ruffians."

"Sure, sure." Dash waved a hand noncommittally. "Now c'mon! It's seven—they're opening the doors!"

Sure enough, they were. Rarity only offered a token protest this time as Dash dragged her to the front of the line and then right through the double glass doors. Once inside, Rarity took a deep breath, and wrinkled her nose when she caught a whiff of plastic and cheap air freshener. Then again, it was better than the horrid stench of musk and sweat she'd been expecting. An artificial atmosphere was simply marvelous compared to that swill.

She followed Rainbow Dash down to the lockers, where the two mares stowed their jackets and bags away in a shared locker. Rarity accepted a hand-towel with a skeptical look—she doubted that she'd need it, and vowed to leave immediately for a shower if she did—but didn't otherwise comment. After that, she followed Rainbow Dash up the stairs to the main area of the gym.

"I'll be over there at the treadmills." Rainbow Dash jabbed a finger toward a long line of large black machines, where one or two ponies were already jogging along at a moderate pace. "You should probably start over there as well to get your heart rate going, but you can try out any of the machines first, just to give it a try."

"Hm." Rarity scanned the line of exercise machines around her with a questioning eye. "What's that one?" she asked, pointing in the direction of a long, flat, black-leather machine.

"That's the rowing machine," Rainbow Dash said. "Good for tightening up your core and burning fat around your glutes." She slapped her tight rear with an open palm, then grinned when a light blush rose beneath Rarity's cheeks. "Should be just what you're looking for, really. Not much of a bulk-up machine."

"Tightening," Rarity mused. "Hm. I was on a rowing team briefly in school." That'd been for all of a single practice, of course, and she'd stormed off after a teammate's oar had splashed a strand of seaweed into her hair, but that wasn't relevant at the moment. "Yes; I think I'll try that."

"Cool." Dash took a gulp of water from her bottle, then screwed the top back on and jabbed a thumb toward the treadmills. "Like I said, you know where to find me. And the machine should have directions on it, but if you need any help with form, feel free to ask."

"Thank you," Rarity said placidly. "But I believe I'll manage quite well on my own." It was just a silly little machine, after all, she reflected. These muscleheads managed to use it regularly, and they didn't seem to have any problem with it. Goodness! Even Rainbow Dash could use it with ease. How hard could it be?

Rainbow Dash wiped the sweat off her forehead. “Whew.” She let her hands rest on her hips as she straightened up. Alright. Now that her stretch routine was over, it was time to -

“Yoo-hoo! Rainbow Dash! Am I doing this right?”

Dash took a second to swig down a gulp of water before jogging over. “What’s up, Rares?”

Rarity was at the rowing machine. She had her legs delicately crossed over one another, and her fingers perfectly positioned with her nails clearly away from the pull-bar. “I’ve been rowing for a full minute, but it just feels odd.”

“That’s cuz your technique’s all off,” Dash said, bending over. “See? You’ve gotta hold out your legs like this and then push off, hard. And you can’t hold your fingers away like that; you’ve got to grip the bar hard and hold it to your chest.”

“But—my manicure!”

“No buts.” Dash shook her head. “You wanted to get buff, right?”

“Get buff! I—nothing of the sort!” Rarity said. “I merely wanted to get more in-shape. But…you say these techniques will improve my form?”

“Gotta do it right if you want to get in shape.”

“Very well,” Rarity said, cautiously. “Thank you, Rainbow Dash.”

As Dash walked away, she failed entirely to notice the small bulges on Rarity’s arms and legs where previously slender limbs had been. It wasn’t a notable gain—two or three pounds of muscle at most—but it was a change. Rarity, for her part, failed to notice them entirely.

As she resumed her workout, though, some part of her mind registered that when she let her muscles relax, they stayed the same size as when they’d been curled. She just kept curling, the sweat on her forehead coming down less and less as her muscles grew and grew.

Soon, the training bra across her chest had grown much tighter, her chest having swelled with muscle as much as her abs had tightened and her hips firmed. Rarity nearly moaned as she made another pull—no proper lady would have done such a thing in public, of course, but it just felt so incredible to have that tightness stretching across what felt like her entire body. She imagined that this was what after-workout soreness felt like, but failed to realize that her workout wasn’t getting harder.

If anything, that same corner of her mind realized as she stood up from the bicep curling machine, it was getting easier—and she was getting bigger.

Just under an hour later, Dash was at the front desk, doing a final towel-off to wipe away any sweat still on her face. She was panting, but just barely. She’d had a good workout. She wondered how Rarity had done.

“Rainbow Dash?” Something thudded on the ground behind her, and she turned around with a smirk, tossing the towel over her shoulder.

“So,” Dash said, “how was your first day at—“

Then she saw Rarity’s straining shirt, saw the muscles rippling beneath the stretched, nearly-ripping sleeves. She saw the thick, corded muscle running down Rarity’s legs, the bulging spheres of Rarity’s tight flank pushing through her track pants. She saw Rarity’s bust, bulging almost to Fluttershy’s size…and then she realized that she was looking Rarity directly in the eye, when she normally should’ve been two or three inches taller.

“What the hay?” Dash nearly jumped. As it was, it felt like every hair on her body had stood on end. Rarity, the prissy little dressmaker who had been barely willing to risk breaking a nail now had Dash’s own physique—if not a little thicker, something deep in her gut noted enviously. “Rares, don’t tell me you took some bodybuilder’s potion off ‘em in the locker room!”

“What, this?” Rarity glanced down at her body, at the straining clothes, at the lean, hard muscle.

“I thought that this was what one did when working out.”

“Not like that!” Dash said, sputtering. “Not that quickly! Holy crud, Rares. I—I…”

“Lookin’ real good, sweetheart!” A wolf-whistle made the two of them turn around. A stallion, his well-rounded pecs bulging through his tight t-shirt, gave the two of them a lazy salute.

“Fuck off, Thunderlane!” Rainbow Dash called. “Don’t you have some corner to jerk off in?”

Thunderlane scoffed. “Not you,” he said. “You couldn’t grow an ounce of muscle if your life depended on it. She’s the one who wears it well.”

Rarity glanced at Dash. “Is...is he talking about me?”

“Better not be,” Dash said, her jaw set. “Lay off, jerkwad.”

Thunderlane just chuckled. With a shrug and a wink, he gave Rarity the silent “call-me” sign, flung a towel over his shoulder, and turned to jog back into the gym.

Rainbow Dash fumed. Dammit. She was the athlete here. She was the one with the muscle, the speed, the power. But as she eyed Rarity’s new size, she couldn’t help but feel a flame of jealousy flare up in her chest. “Fucker,” she growled.

“Dear, are you alright?”

“Fine,” she bit out. Rarity looked vaguely concerned.

“Because I don’t really mind what he said. They’re just words.” Rarity looked thoughtful. “In fact, I rather enjoyed the compliment.” She gave her arm a light flex, and watched the sizable bicep there bulk up before relaxing it. Neither noticed that when she let the flex go, her arm stayed slightly larger than when she’d started. “I wasn’t so sure about the gym at first, but I think I’m rather enjoying the effects. How long did you say you’ve been coming here, again?”

How long—oh, hell, she was not going to answer that. She wasn’t about to let Rarity show her up. No prissy, stuck-up unicorn was going to get more attention than her at the gym. Friend or not, she wasn’t about to let somepony who’d rather stay home than break a nail come off as bigger than her. The first workout must have been a fluke. She eyed Rarity’s biceps, tried to make them seem smaller than the bulging slabs of muscle they were in her mind. She mentally pushed Rarity’s height back down to eye level. She’d been looking down at her for too long to admit that they were of even height now.

Rainbow Dash was on the warpath, and she was going to show how much stronger she was than that prissy little unicorn. She yanked Rarity by the arm and made toward the gym. “C’mon, Rares. Let’s have another go.” Thunderlane would see who wore it better. Fuck endurance training. If he wanted muscles, he’d get muscle. And Rarity would see, compliments or not, who the real strongpony was.

Rarity stared bemusedly down at the pair of weights lying on the mat before her. “Are you sure, Rainbow Dash? They seem a bit...larger than what some of these other ponies are using.”

“They’re fine,” Dash said. She hefted her own pair of dumbbells up to her chest and smirked. If Rarity wanted a workout, she’d get a workout—Rainbow Dash style. There was no way Rarity could handle two twenty-pounders, no matter how many steroids she’d stuck in her water bottle that morning. She did a few curls, grinning when she felt that pump going in her upper arm. Oh, yeah. Now that was why she worked out. “They’ll probably be a bit too heavy for you, so don’t feel too bad if you have to move down to fifteen pounds. Or even ten. Just—”

But Rarity was already bending over to pick up her new weights. Her firm, muscular glutes pushed against the seat of her shorts, two spherical cheeks flexing with her core as she leaned down. She grabbed the dumbbells, then, with a short huff of breath, pulled herself back into a standing position, the weights curled against her chest much like Dash’s. While she didn’t seem to be having an easy time holding them, they certainly didn’t seem too heavy in her grip.

Dash scowled. When she’d first started, it’d taken her two weeks to work up to these! She had to play it cool, though, she told herself. Maybe Rarity’s were off-balance, or too light. And with a beginner’s form, there was no way she’d have an easy time of it after a set or three.

She was soon proved wrong. As Dash finished her fourth set of reps, she turned her head slightly to find that Rarity was close behind. If anything, Rarity was pumping iron a fraction of a second faster than she was. In most cases, she’d be able to dismiss that bad form. But as they started up a sixth set, Dash was forced to admit that Rarity barely looked winded at all, and was only speeding up.

Rarity was enjoying herself. She’d lost count of the number of “sets” they’d done, but she made sure to count every “rep” she did. She held her weights out in front of her, palms up, with her elbows tight to her chest. Her bust, a bit larger than it had been that morning, squished a bit beneath their weight. Rarity took a deep breath, closed her eyes, and resumed her reps.

Up and down the weights went, her thick arms steadily pumping them up and down. Breathe in, breathe out. Rarity’s arms flexed, her biceps and triceps bulging a little bigger, and staying a little bigger, with each rep. She could almost feel her muscles growing firmer, her chest pushing against her thickening arms, her bust swelling and rising with every breath.

About halfway through her seventh set of ten, Rarity realized that she couldn’t quite feel the weights anymore. It felt like she was just lifting her arms up and down. A slight frown on her face, she opened her eyes and glanced down at the weights in her hands. They were still there—she hadn’t dropped them or anything—but they felt lighter. They looked different, too. Smaller perhaps.

Now that was odd. Rarity shrugged her shoulders, causing her impressive lats and traps to bulge out behind her. Her biceps and chest flexed, straining against a suddenly tight training bra. She tugged at her shorts; for some reason, they looked smaller than they had this morning. Were those her knees poking out from underneath the legs? They’d gone halfway down to her shins earlier.

She actually had to loosen the front string to get some breathing room. When she pulled her hand back up her stomach, she was rather pleased to find three pairs of smooth, firm ab muscles rippling beneath her touch. Her hand hovered for a moment, then darted downward to give the space between her legs a short, heated stroke. Rarity shivered with pleasure, her every muscle momentarily flexing and swelling in size. When she pulled her hand away, her tighter panties felt more than a little bit damp.

She glanced to her left. “Rainbow Dash,” she said. “What should I do if my weights are feeling a bit too, ah, light?”

Dash froze mid-rep, turned, and stared at her. Or, more accurately, stared up at her. For Rarity’s eyes now came up to just above the tips of Rainbow’s ears. The rest of her body now bulged even bigger: her arms had to be three or four more inches around than Dash’s, and her already-impressive bust now put Rainbow’s flat chest to absolute shame.

Rainbow Dash flushed angrily. “You can’t mean—”

She cut herself off. “I mean,” she said, after taking a deep breath, “there’s no way those’re too light.” She tried to force a cocky grin onto her face. “Maybe you’re just fatigued from working too much.”

Rarity caught the blush on Dash’s face, noticed their difference in height. On a whim, she gave her larger arm a bit of a flex—and then grinned internally when she saw that blush deepen. Oho. So that was how it was, hm? She could enjoy this.

“I don’t think so.” Rarity set her weights down and frowned. She took only a moment to refind the dumbbell rack. She inspected a few before a particular pair caught her eye. “Ah! These look much better.”

“You’ve gotta be kidding,” Dash said as Rarity made to pick up a pair of fifty-pounders. “There’s no way you can lift those.”

But lift them Rarity did, and with just as much ease as she had her first pair. Rainbow Dash’s eyes bulged, and she almost threw her own weights down right then and there. What the hell? She could barely curl thirty-pound weights, let alone fifty!

Rarity gave her new weights a few experimental lifts. Much better. She could feel her biceps curling against a proper amount of resistance again. “These should do,” she said.

Scowling, Rainbow stalked over to Rarity and glared up at her. “Gimme those,” she said. “They must be badly made or something.”

With a shrug, Rarity placed the two weights on the ground. When Rainbow Dash tried to lift them, though, she felt a huge resistance pulling her arms down. She managed to get them to waist level, but the second she tried to heft them to her chest, the weight pulled her arms right back down. She nearly crashed to the floor before Rarity caught her.

“Get off me,” Dash spat, dropping the weights and pushing Rarity away. She picked up her own twenty-pound weights, eyed them, and then dropped them back onto the floor. “Y’know what? That’s enough for these arm workouts. Let’s try some benching.”

“I’ve been working on these for a while,” she said as she settled herself down onto the weight bench. She pushed underneath the barbell, readied her grip on the iron bar. “I got up to two hundred pounds just last week. Not many mares can say that, huh?”

“I suppose not,” Rarity said mildly. She observed the weight that Dash was about to lift and couldn’t help adding, “Though from here, it doesn’t seem like quite a lot.”

Dash flushed. “That’s because you’ve never done this before.” With a low grunt, she began her reps.

Rarity watched her go with a mild disinterest, her arms crossed underneath her impressive bosom. When Rainbow finished—with a smirk and a “Ha! Top that.”—she couldn’t help but go over to the barbell herself and lift it a few inches into the air.

She shook her head sadly and let it fall back down. “Far too light, I’m afraid.” She began to search for more weights.

“No way,” Rainbow Dash said incredulously. She could almost swear that Rarity looked a few inches taller than she had just minutes previously. At five-foot eleven, Dash was no short mare, but Rarity looked to be pushing six feet, four inches easily.

“You can’t lift that much,” Rainbow said as Rarity finished sliding her last weight onto the bar. Four hundred pounds—twice as much as Rainbow has been able to lift. “I don’t know anypony who can.”

Rarity slid underneath the bar. “Perhaps you do,” she said teasingly.

 Her fingers clenched around the cold steel, her muscular forearm bulging out even further. And she began to lift. It was a wonderful feeling. With every half-dozen reps, it seemed, she could see her muscles bulging out a little bigger, her limbs growing a bit longer, her bra feeling a little tighter around her chest. Rainbow Dash watched with awe as Rarity’s massive frame grew even huger, her arms swelling out thicker, her legs growing to the size of tree trunks, and her waist expanding until it overflowed the bench.

“Mm,” Rarity moaned lightly. “This feels so good.”

Up and down the barbell went—at first, with some difficulty, and then more and more easily as Rarity grew more than big enough to compensate. She grunted with pleasure every time she finished a pump, really savoring the feeling. She loved feeling that weight dwindle to nothingness as she grew larger and stronger, as she could feel throughout her whole body. She loved knowing that nopony could even hope to lift this much weight, and that even this was beginning to feel light to her.

Finally, when she felt there was no point in continuing to lift, she let the bar drop back down into place. Her erect nipples were actually squished against it; her massive breasts were overflowing both the bra and the bar. Rarity smirked, then merely picked up the dumbbell in a single hand, and let it drop off to the side to make room for her to sit up.

It hit the ground with a magnificent clang. Inhaling deeply, Rarity pulled herself up and gazed pleasantly at Rainbow Dash. Instantly, Rainbow realized that Rarity was looking her in the eyes—and she was still sitting down.

“A wonderful workout,” Rarity said, fluttering her eyelashes. “I must admit, I’m truly beginning to see why you enjoy this so much.” She felt a sudden urge to show off her new size, and heaved herself to her feet, her magnificent breasts bouncing lightly against her chest as she did so.

Rainbow actually stepped back as Rarity drew herself up to her full height. Dash felt her heart thudding in her chest. She felt lightheaded.

At least seven feet tall if she was an inch, Rarity was a true marvel now. Her training bra had been stretched to a spaghetti string, and now covered up little more than her straining, erect nipples. Her workout shorts looked about ready to burst off of her, and came just halfway down her calves. She grinned down at Rainbow Dash.

“Goodness,” Rarity said. She flexed an arm, admiring the way it bulged out nearly as large as her head. She absolutely towered over the other mare now, and she absolutely knew it. She gave her arm a few more flexes, as if curling an imaginary weight, and was rewarded when that familiar flush grew on Rainbow Dash’s face once more. “What a body! Rainbow, why don’t you have a body like this if you work out so much?”

“I don’t know, Rarity,” Rainbow Dash growled. The shock was over; barely restrained rage had set back in. “Why don’t you tell me?”

“Perhaps some ponies are just more gifted than others,” Rarity said, after a moment’s thought. She reached down and picked up the four-hundred-pound barbell, hefted it thoughtfully in her right hand. “I thought you said that this would be heavy, darling. It hardly feels that way.”

Her eyes drifted down to her massive, straining bust. “And goodness! I never dreamed that exercise could help one’s figure in this way.” Almost unconsciously, her hands drifted toward the underside of her enormous boobs, massaging the taut, supply flesh. “I do wonder why it never brought you more than those small peaches. But I certainly appreciate all that it’s done for me.”

She was rubbing her nipples now, massaging through her bra’s thin, overstretched fabric. Her thimble-sized nipples throbbed in response, dampening the cloth. “Ooh,” Rarity moaned under her breath. “They feel so good…”

“Rarity!” Dash snapped. She was breathing heavily. She noticed a trickle of clear liquid dripping down the inside of Rarity’s muscular thigh, and nearly snarled. “That’s enough.”

The amazon paused. “Enough of what?” she asked innocently. Her hands didn’t leave her breasts.

“Y’know what?” Dash said. “We still haven’t done a proper back squat. I’m going to show you how it’s really done.” That was it, she told herself. No more Miss Nice Pegasus. That oversized, arrogant prissy little mare needed to be shown how a proper iron-pony did things.

Showing her the squatting barbells, Rainbow Dash did her best to lift a three-hundred-and-fifty-pound weight—fifty pounds heavier than her normal weight, but she barely even cared anymore. She was sweating, but proud, when she managed to make it through a whole set of twelve reps with the thing. She nearly collapsed to the ground when she finished, but show Rarity a victorious grin at the end.

Rarity eyed the weight skeptically. Too late, Rainbow Dash recalled that her much larger friend had easily manhandled four hundred pounds of weight with a single arm not minutes before. Before she could speak, though, Rarity had already made her way over to the weight rack, where all of the barbell components were securely bolted into place, and seized that with both hands.

Rainbow Dash’s eyes bulged as Rarity, grunting and straining and sweating, managed to lift nearly a full ton of weight a foot into the air. Then a few more inches. Then a few more. She could hear clothing stretching; her ears were filled with Rarity’s grunts of strain as her massive friend brought her equally massive weight up to her waist, then to her chest. She could see Rarity growing in real time, now, her head shooting up above her, her arms bulging bigger and bigger by the second as her muscles rippled all across her body, her stance widening with every additional inch.

Rainbow Dash trembled. Her friend had to be over eight feet tall by now, possibly closer to nine. Her muscles bulged all over, from her huge, muscular ass (which was more than overflowing her close-to-ripping shorts), to her humongous chest (which made her training bra look more like a piece of string), or to her massive arms or tree-trunk legs. Rainbow Dash gulped when she realized that the top of her ears just barely passed Rarity’s underboob; those full, throbbing nipples bobbed pleasantly a full foot above her head.

She glanced down, and paled even further. Rarity’s expanding waist and ass had stretched out her shorts into something more resembling a thong. The whole process had left behind a cameltoe that was more than obvious, and which was leaking a steady stream of femjuices into the towering mare’s already damp panties. It was clear that, whether Rarity had consciously recognized the full extent of her size or not, she was certainly enjoying it to the fullest.

Rainbow Dash resisted the urge to let her own fingers stray toward her suddenly burning marehood. No, dammit! She wasn’t going to get turned on by Rarity getting so much bigger than she was! How the hell was this even possible? Nopony bulked up or grew that fast! She would have voiced those questions, but all that came out of her mouth was a vague “bluh, gah, eugh.”

Rarity didn’t even pay her a glance. She was too busy with her herculean task. With a mighty grunt, she hefted her one-ton weight above her head. Her biceps bulged up bigger than either pony’s torso, her massive, beefy forearms bulging with power as she blasted the iron-pony weight past her ZZ-cup bust.

Her massive legs flexed against her straining shorts all the way. Her bra string was quivering as gallons of titflesh overflowed it. Every muscle in Rarity’s massive body was trembling, quivering with untold power. With an equally massive grunt, Rarity squatted back down, her impossible weight on her shoulders—and then pushed herself back up.

One rep. Two reps. Three. Five. Ten. Rarity didn’t stop there, though. She just kept going—and kept growing. Dash watched in stunned amazement as the once-dainty mare added another inch or two in height in a single breath, and another two-dozen pounds in muscle mass.

“Much better,” Rarity moaned. Finally, she could get a proper workout. “Ooh, I’ve been waiting for a weight this good all morning!”

She pumped her incredible weight once, then twice, then three times, each time her massive arms bulging and flexing a little—and soon, a lot—bigger as she hefted her ton-plus weight over her head again and again. Her lats and traps bulged out enormously, and she quickly surged up another half-foot in height.

“Ooh,” Rarity moaned again, looming over them. “I can’t get over how good this feels, Rainbow Dash. I can feel my muscles growing, getting stronger, getting bigger.” She hit nine feet and passed it without breaking a sweat. “You’re starting to look so small down there beneath me.” It was true. Each pump was getting easier, each rep feeling lighter in her massive hands. Rainbow Dash felt the ground drop out from under her and collapsed to her knees, watching helplessly as Rarity grew into a titan.

“Mm.” Rarity closed her eyes. “Look at my wonderful breasts—so big, so soft, so firm. And yours, barely even pushing up against your bra. Oh, and these arms. Have you seen any of such a size? Goodness, but flexing them feels so good. I understand now why you love coming here so much. Lifting, pumping, growing, getting stronger and stronger with every new weight—

“Ooh, yes.” Rarity tossed her head back, her chest bulging out obscenely in front of her. An ominous creaking had filled the air, the fabric making up her shorts and bra straining in a last-ditch effort to hold in Rarity’s growing mass. By now, she was taller than the lights hanging from the ceiling; soon after that, Dash’s face would have only barely reached Rarity’s belly button. No—her crotch. “Bigger,” Rarity moaned. “Bigger. Bigger.” She’d switched off from pumping with both hands to pumping with one, her right arm doing rep after rep of the one-ton weight as her left roamed down toward her legs. Juices were streaming down her massive thighs, every muscle on her enormous body flexing and growing at once—

“Bigger,” Rarity moaned. “Bigger,” she demanded. “Bigger, bigger, bigger!” Her bra strained, her shorts screamed—and with a final, massive pump, finally gave up. Rainbow Dash winced as she heard clothing fibers popping and shredding audibly, Rarity’s shorts shredding into tattered ribbons as her bra simply burst off of her. It hit Dash in the face and slammed her to the floor.

“Big—augh!” Rarity let out a scream of pure pleasure and delight as her orgasm hit her. She revelled in the size, in the power she felt as she rode it out, every muscle in her massive body flexing, bulging, growing in size with every convulsion of her inner walls around her fingers. She shot up and up and up, leaving behind the tattered rags of her former clothes as her marehood and breasts exploded free, her whole body growing past ten feet, eleven, twelve in a torrent of growth—

Her orgasm finally finished. Rarity let the massive weight drop to the ground, and panted gently. The whole ground shook from the force of her one-ton weight. Rainbow Dash stared up at the hulking titan. If not for the incredibly high ceiling of the gym, Rarity’s ears would be brushing up against the roof right now. As it was, Dash doubted she’d ever be able to fit into a normal-sized house again.

But Rarity didn’t seem to care. She was too busy glorying in her newfound size, her face flushed with pleasure and self-worship as her hungry fingers, dripping with her own juices, roved hungrily over her massive, bulging, rippling body.

Dash just couldn’t take it anymore. She wanted to scream, wanted to rage, wanted to explode—but she just couldn’t take it anymore. Fuck this; fuck Rarity; fuck Thunderlane. Fuck the universe for giving her a pretty little friend who suddenly decided to grow twice as big as gods-damned Celestia—

“Well?” Rarity said, her richer voice ringing out in Rainbow Dash’s ears. Dash winced, then glanced up at her larger friend. “What do you think?”

Every inch of her larger friend’s massive, hulking body filled her vision, and she wasn’t sure if she loved it, hated it, or wanted it. Probably all three. Dash took a deep breath. “You win,” she said in a small voice.

Rarity gave her a little smirk. “Win what?” she asked innocently. She folded her arms beneath her massive chest, apparently ignorant of her complete and utter nakedness before the rest of the gym. The ponies around her, though, were absolutely anything but ignorant. They ogled, babbled, and all in all worshipped the massive muscle titan that had come striding through their gym.

Rainbow Dash held out a hand, then weakly let it drop to her side. “Everything,” she spat. “You’re stronger than me. Bigger than me. Better than me at anything. I wanted to show off, to prove that I was better than you in some dumb competition...but all it did was make you bigger.”

An elegant eyebrow folded on Rarity’s forehead. “Is that so?” she asked pleasantly. “I hardly noticed a competition at all.”

Dash gritted her teeth and forced down a scream.

A smile crossed Rarity’s face. “I did rather enjoy this light workout. Perhaps we could come back tomorrow? I think I’ll accompany you here from now on.” Her two sausage-thick fingers crept back up toward her nipples and began to fondle them lightly.

“Mm,” Rarity purred. “Perhaps I can even give you some tips on getting bigger, as it were. To become such a fine specimen as myself.”

This time, Rainbow Dash didn’t bother to keep herself from screaming.