Hot Swap

“Okay students! Pull out your geometry textbooks because we’re having one heck of a fun lecture today! Be sure to copy everything I write on the board and you’ll be math masters in no time!”

Rumble groaned in sync with half the class and pulled his textbook out. Miss Cheerilee’s class wasn’t terrible but it was painful to sit thru on subjects that weren’t interesting. Math was one of those subjects and Rumble was already wishing the day was over. He had woken up in a pool of sweat and had felt very uncomfortable all morning. Even a cold shower hadn’t helped. All he wanted was to go for a dip in the lake after class. Or sit inside a rain cloud.

Rumble was also down to his last pieces of clean clothes before laundry day: a thin, slightly undersized short sleeved buttoned down dress shirt he typically wore on nice family outings and a pair of jeans that had ripped just above the knee. Nice clothes and fashion weren’t alien to Rumble but this is what he had to work with. Rumble unbuttoned the top button to help vent how uncomfortably warm he was. It didn’t feel like a fever. It was as if he’d just done a marathon in the hot sun.

“-once the Pythagorean Theorem is correctly utilized it leads you to a greater understanding of working out the formula for these shapes.” continued Cheerilee with gusto. It only took five minutes of math lecture before Rumble officially zoned out. Even in the back left of the room he wasn’t THAT far away… but today was different. The warm creeping feeling under his coat was making him glassy eyed and his mind started to wander.

Cheerilee was wearing a warm blue collared polo that was juuust tantalizingly too small for her. It hugged the contours of her generously sized breasts in a way that couldn’t be ignored. The hem of the shirt just barely reached the black skirt she was wearing, which meant every twist and turn flashed a subtle line of purple belly for all to see. Said black skirt was tight and hugged her hips perfectly. It ended about mid-thigh on her and displayed her thick, shapely legs.

“Mmm,” Rumble almost moaned out loud. He glanced down at his lap and noticed his very hard erection had snaked halfway down his pants leg. Cheerilee was usually boner inducing but not typically like this. Or this fast. His breathing was shallow and he could feel his heart-rate spike.

Luckily none of the other students had noticed. They were busily scribbling away or also staring off into space. Rumble tried to focus on writing down numbers but in his incredibly aroused and flustered state he realized it was futile.

He needed some attention.

Rumble shakily crept his left hand to his leg and gently massaged his aching rod.

“Ng,” Rumble bit his lip. That felt really good for just a touch! It was so sensitive and the pang of arousal was so strong he had to do it again. Nobody could see what he was doing anyway and he was pretty confident about his self control to play with himself just enough to tire out his demanding cock.

Rumble kept stroking and his cock just kept feeling better. The pleasure undulating in waves of pleasure. He imagined Cheerilee bent over her desk after class, her skirt hiked up and revealing her shapely, round ass. His teacher cooing his name and demanding a rough fuck before the day starts for school. Smacking the smiling sunflowers on her ass over and over again while she cries his name.

The erotic fantasy was so powerfully arousing he had to stop stroking and clench his fist to keep himself under control. His cock was throbbing powerfully in his jeans, and the minute sensations of the fabric just touching his erection were fanning the flames. He didn’t HAVE to touch his dick anymore. Rumble shifted in his seat and he swore it was almost enough to make him cum! Instead, he just felt on edge. After ignoring the building arousal and teetering on the precipice of orgasm for ten seconds Rumble gave up. Mess be damned he was going to cum.

Rumble placed his hand on his thigh to finish himself off and…

Felt nothing there.

Confused, Rumble scooted back in his seat a bit and looked at his pants leg. His previously strained jeans were now looser, and his formerly erect cock was much closer to his groin now. The small bulge in his pants looked like how it was flaccid. Yet when Rumble touched it the stiff organ twitched firmly and sent a wave of pleasure thru his entire body. His penis twitched, and then shrank another inch before his eyes.

It was like watching something die. Rumble felt a cold sweat break on his overheated body. This wasn’t normal. It had to be the potion doing this somehow! But why now? Why in class? Why was it making his junk smaller instead of bigger? Rumble scratched his itching chest while his mind raced for answers.

He tried to gingerly shift into a different seating position but instead only served to further stimulate his tiny cock. Another wave of pleasure shot thru his body and Rumble could only brace himself against the desk as what felt like some sort of mini-orgasm overtook his body. In slow pulses he watched as the bulge in his pants dissapeared completely with each orgasmic flex of his groin until…

Nothing. His penis was gone.

Rumble gulped heavily. That was the last time he ever took a potion.

The clock on the wall read that only 11 minutes had passed and Rumble stilll had 50 minutes to go to not somehow get caught that he’d just switched his sex in class. Rumble breathed deeply. He still looked like himself going by the plastic reflection of his notebook cover. All he had to do was relax. Relax and not worry about getting caught.

Unfortunately the potion he drank was working overtime.

Rumble idly scratched at his chest again and recoiled when he brushed across his nipple. The stab of pleasure was more pronounced than he’d ever felt there before. Making sure that nobody was looking, he pulled the front of his shirt forward as little as he could to peek down. Sure enough, his once unnoticable nipples had fattened and rounded to little dark grey nubs. Both of them stood erect on the dark hills of his newly spread areola; which were wider than silver dollars. He quickly stopped looking as to not draw attention to himself but the fabric rubbed against his nipples and he felt the twin peaks of pleasure pulse through him again.

He was growing breasts.

Small ones, sure, but for how long would they stay small? He still had a brand new sopping wet vagina tucked between his legs and that burning arousal was still there. Instead of feeling hard and powerful now he felt slippery… and receptive. Briefly the thought of a hard cock slipping between his new pussy invaded his mind.

“Nngh,” Rumble actually moaned. By Celestia’s grace the chalk in Cheerilee’s hand screeched at the exact moment and nopony heard. But the arousing thought caused his pussy to flex and his chest to throb. Rumble shook his head. All he needed was to sit to the bell.

But his mind was elsewhere. It was in Cheerilee’s bosom, writing around while she sensually made out with him on the school desk in front of the class discussing the proper ways to give relief to a horny mare in need and-

Rumble shook his head to snap out of it and felt something even more worrying: his hair. Reaching his hand up behind his head he felt his normally short head of slate grey hair extending down to mid-neck level. It also felt different. Fuller. Weightier even. He twisted his torso in his seat and saw not only his tail having grown longer, but his ass… it looked STUFFED into his normally well fitting jeans, and Rumble slid his hand down to it to confirm it was real. His ass and hips were slowly widening.

He was turning full on female.

The sensual thoughts made him twist back to attention and he became aware of another brand new sensation of his chest jiggling. His breast buds had graduated into an A cup and his nipples were poking up against his shirt already. It felt really, really nice and Rumble stiffened up. He undid his belt and quietly pinned his wings to his back to prevent any random wing boners. Last thing he wanted was to be on full display for every boy in the class to ogle at.

A sharp pain flashed thru his head and Rumble winced for a split-second. Then it was gone, and Rumble could breathe again.

Rumble sniffed the air and he felt his pussy throb even harder.

Because there were many more ponies enrolled than the classroom could fit, Cheerilee had split the classes into two and taught them on alternate days on and off. One class was mostly boys, the other mostly girls. Rumble was in the boys group and now he could feel it in the air. Was the room always this permeated with such strong musk? The aroma of masculinity drifted thru the air and Rumble sniffed the air again. It was almost intoxicating. Rumble didn’t even realize he’d planted one hand down to his soaked pussy.

Cr-e-e-e-ak

His once roomy jean shorts groaned as his legs packed on supple layers of fat in his thighs and ass. Now there were no hints of wrinkles except around his crotch as the space inside was greedily sucked up by his expanding assets. The sensation of massaging his needy pussy brought a silent gasp to his plumping lips. It was so good! His chest heaved and fell, the small breasts encased inside swelling larger with each breath. In minutes his buttoned up shirt was straining against a 34-C cup pair of tits, the dark nipples having lengthened another inch and seriously tenting the fabric.

Rumble had to stop. If he got caught he’d never live it down. He removed his hand and his pussy winked hard, demanding attention.

The damage done playing with himself for just a minute was enormous. In the semi-transparent reflection of his desk Rumble could really note the differences. His eyes had seemingly grown bigger on his face. Or maybe that was just a result of his longer, thicker lashes? His nose had shrunk and was slightly upturned. Gone was his squared off jaw: now his vaguely pointed chin and widows peak gave his face a vague heart shape. His hair had grown to his shoulders and had a subtle sheen to it now. And his breasts...

In his slim boys shirt they looked as if two melons were stuffed down into his chest. The erect nipples tented unmistakable peaks that would arouse any male. He traced his finger down the front and noted the already slightly strained buttons. Down at his waist the previous subtle traces of 6-pack abs were gone, replaced by a soft belly, his bellybutton deepset. His thighs were packed into his jeans now, the flesh bulging at the cutoffs, and then his ass.

Rumble didn’t want to look, but he could feel his new fat ass packed into the jeans. He swished his tail and felt the weighty mass of hair pulling it down. He slid down in his seat and realized by doing so he could kind of hide his new breasts. Not only had he grown, but he’d also shrunk in height.

He might have bigger breasts than Silver Spoon now.

The thought of surpassing the bustiest girl in class sent a flash of pleasure thru his body and his breasts surged into D cups breasts, and then DD. He arched his back and winced trying to control his urges, but instead one of the buttons broke off his shirt, revealing inches of light grey cleavage to anyone who was looking.

Rumble slumped forwards, crushing his fattened tits into the desk. Had anyone noticed? All the other students seemed to be focused on the math. Cheerilee was still carving numbers onto the board, her fat ass wiggling left and right.

Another surge of growth rocked his body and his growing breasts demanded space. Rumble leaned back and while adjusting his seat realized he’d shrunk so much that his hooves weren’t even braced flat on the floor. Only the tips of them were touching.

He had to stop himself. But he couldn’t. His big breasts were clearly outlined in his shirt and due to his sweating, the white fabric made it practically see through. Anyone who looked would see his tightly packed tits and fat, dark nipples if they pleased to look.

The musk in the air wasn’t helping either. In fact it only spurred his arousal further. His hair grew out down to his shoulder-blades, tip of his grey tail following suit. His pants tightened so much Rumble reached down to unbutton the clip. And a second later unzipped it too. The brief touch near his crotch spiraled him ever closer to another orgasm.

In his fantasy it was him and Cheerilee on the teachers desk, splayed over, naked, and moaning lewdly. Cheerilee was gripping the desk while being rutted with all her might, tits hanging out of her bra, eyes rolling up her head and drooling. Right next to her was Rumble, being fucked just as roughly and his own tits, bigger and fatter than his teacher pressed against the desks surface and undulating with each powerful thrust.

Rumbles shirt BULGED with the growth of his tits and two buttons popped out in the rapid surge of mass. His hips and thighs swelled. Tears appeared on the jeans legs and his rear where his tail jutted out. By the time his growth spurt ended he had absolutely surpassed Cheerilee’s generous rack. Maybe even then some.

That thought triggered another spurt and Rumble was more than certain. He had gone from losing his junk to fully endowed female in the span of twenty minutes. His face was beautiful, his ass wide and plump, and his tits had to be the envy of the town. Maybe even the royalty too. He could imagine their faces when comparing their willowy statuesque bodies to his sexy new curvaceous look.

Another spurt of growth kicked in and Rumbles shirt quivered. It was on the verge of exploding off his body! So impossibly stuffed to the brink with his huge new EE cup tits. The large melons pulled up enough shirt fabric that his soft midriff was now permanently exposed. Rumbles hooves dangled in the air above the floor, having lost maybe a foot of height. Maybe more? In any case the bell was about to ring and thankfully he had maintained his composure and nopony noticed he-

Rumble glanced and did a double take to his left. Pip was staring right at him.

He froze like a deer in headlights. Was he so engrossed in his own body that he failed to notice he was being watched? Nopony else seemed to have noticed but Pip had. The proximity was just far enough away. Could Pip tell what…

Of course he was. To make matters worse Pip was obviously stroking his own erection thru his gym shorts.

Rumble bit his lip. His mind immediately raced to the gutter. He was back on the desk in his sexy feminie body being railed by Pip, being fucked by his classmate who he formerly towered over, but was now shorter by a few inches. Then being pumped full of cum and screaming his name.

A powerful surge of arousal gripped Rumbles body and his shirt lost two more buttons as pounds of new breast flesh rushed forwards. Several inches of cleavage wobbled dangerously in the air. A few more buttons and Rumbles now enormous chest would pop out into the open for the entire classroom to see, all the boys and girls and Cheerilee ogling the tremendous tits he sported.

DING DING DING DING

The bell rang out right as twin tears erupted on Rumbles jeans, exposing his grey thighs.

“Now remember! Practice questions 1A-20A on page 149 for homework!” Cheerilee said sweetly. “I’ll be checking so do your work!”

Rumble hastily jumped out of his seat and swung himself behind it to try and hide himself, nearly falling over in the process. He had shrunk so much and his center of balance was completely off due to the weighty new mass on his chest. Unbuckling his belt wasn’t even necessary, as his torso had slimmed to give him an hourglass figure; the loop just fell and rested atop his widened hips. Rumble spread his wings and bolted out the door with his bookbag in hand.