“Wait a minute,” Twilight blurted out. “Um. Sorry. Could we back up a second?”

Celestia leaned back in her throne. She eyed Twilight calmly. Her ethereal mane floated gently beside her. “Of course.”

“Testing,” Twilight said. “As in, testing me? For what?”

“I thought it obvious. To see how big you can get.”

Twilight whirled. “Princess Luna!”

Luna smiled, and let the door swing shut behind her. “A fine goal, don’t you think? Especially given your new...stature.”

Twilight hadn’t expected this. She felt a stirring at her crotch and glanced down hurriedly. Why Luna was sashaying her hips, she didn’t exactly want to know. “But I thought the whole point was to get me smaller.”

“Now what might have given you that idea?” Twilight felt a weight on her shoulder and looked up. With some amount of surprise, she found that she was looking straight into Luna’s eyes. The other alicorn smirked. “I confess, I haven’t had to look up to a pony other than my sister in...millenia. I must confess, I’m rather savoring the opportunity.”

“No, no.” Twilight stepped back. “I thought—that is, I wanted the two of you to help me get control of...well…” She turned back to Celestia and waved a hand awkwardly over her body. “This!”

“And we will,” Celestia said. She stood up.

Twilight swallowed as Celestia’s dress cascaded around her, the hem swishing softly around her ankles as she made her way down the steps. The Princess’ long legs cut wide strides across the marble throne room floor.

Twilight had always known that her mentor cut a shapely figure—many ponies considered her the most beautiful mare in Equestria. Yet, aside from a healthy respect for her beauty, Twilight had never before really considered Celestia in...that way. Now, she found herself eyeing the twin mounds at Celestia’s chest with newfound interest. Her heart nearly stopped when her eyes drifted a bit lower and saw a smaller, yet no less impressive bulge, centered right at Celestia’s crotch.

Of course she had one too. How could she not have realized?

“I’ll be happy to help you, my student,” Celestia said. She swept across the floor and laid a hand on Twilight’s shoulder. Though she was now, nearly, of a height with the eight-foot-six Luna, Twilight was grateful to still be shorter than her lifelong teacher. It felt...proper. “But you must understand that there is much you do not know of your…” She gave Luna a glance. “...predicament.”

“I’ll listen,” Twilight said. “Really. Just...please, help me.”

A smile touched Celestia’s lips, and, like a foal, Twilight instantly felt that everything would be fine. “Of course,” Celestia murmured. Then she stepped away.

“The size of an alicorn,” she began, “is not strictly a biological phenomenon. Each of us has a base form, a group of certain ‘normal’ attributes. Upon ascension, though, we...grow.”

“How much depends on the source of our power,” Luna cut in. “The Moon, for me; the Sun for my sister. Princess Cadance, for example, draws power from love.”

“A more powerful energy than either of ours,” Celestia added. “She’ll be larger than us before long.”

Twilight blinked, thinking back. It was true...she did remember Cadance being smaller when she’d been her foalsitter. But she’d just written it off. “So that’s why I’m growing?” she asked. “Because I’m now the princess of…”

“Friendship,” Celestia said. “Or magic, if you like. They’re roughly synonymous.”

“Such power,” Luna said, “is equivalent to that of the Elements of Harmony themselves. Even Cadance is still six inches shorter than I. She has time to grow—as do you.”

“With such a potent source of energy,” Celestia said, offering Twilight a smile, “it’s little wonder that your size has increased so dramatically, and in such a short period of time.”

“That...makes sense,” Twilight mumbled. “But what about the...sexual stuff?” She blushed. “I shouldn’t be getting this, well, turned on at everything. And the, erm, genitalia.”

Celestia and Luna exchanged glances. “As a Princess,” Luna began, “you are now a representative of all of Equestria—thus, your body has shifted sexually to fit. I’m sure you’ve noticed that you’ve retained your marehood as well.”

Twilight nodded meekly.

“As for the libido…” Celestia shrugged. “It’s a part of our mantles that we be encouraged to be highly fertile and driven, especially during the early years of our ascension. To intermingle one’s power with the populace provides for a stronger, more united Equestria in the future.”

Twilight’s ears burned. “Wait. You mean that I’m expected to—”

“Yes,” Luna said cheerily. “As frequently and as widely as possible.”

She had not just heard that. The stiffening pressure down her leg, though, was proving otherwise. Her mind was suddenly assaulted with images: Fluttershy’s big, bouncy chest; Rarity’s smooth, lithe curves; Applejack’s muscles; Rainbow Dash’s tight rump—

She shook her head clear. “I—I don’t really want to think about that right now,” Twilight said. “If you don’t mind. I just want to get this under control.”

“Of course, Twilight,” Celestia said kindly.

“Especially my growth spurts,” Twilight said. “One minute, I’ll be my normal height—” whatever that meant anymore “—and the next I’ll be twice that. Or even bigger!”

“Ah,” Celestia said. She pursed her lips. “That is indeed another part of your magic. Watch.” Luna lightly nudged Twilight aside and walked over to join her sister. Staring, and still blushing faintly, Twilight waited for Celestia to continue.

Then, Twilight gasping in the background, Celestia took her sister in her arms and kissed her on the lips.

It wasn’t a chaste kiss, either—definitely nothing one could expect to see between siblings. No; Celestia was kissing her hard, and Luna was pushing back into it with just as much force. The two siblings’ muzzles dueled, their busts squishing outward as they forced their mouths closer and closer together. There was undoubtedly tongue involved.

Twilight’s cheeks burned as Luna moaned into her sister’s lips, her hands roaming down to Celestia’s thighs and squeezing. Oh, yes. There was definitely tongue.

Celestia was getting into it too. She was swaying back and forth, her crotch grinding gently against Luna’s. As Twilight watched, her mouth agape, two large shapes pushed up between the Princess’ cleavage—two very phallic shapes. Celestia suckled on Luna’s mouth, her fingers grasping hungrily for her sister’s fat, supple ass.

Their shafts stiffened between them, the constant jerking of both sisters’ hips frotting them against one another. Twilight’s ears felt like they were on fire, and some innocent part of her yearned to look away. But she felt powerless to keep her own hand from drifting down toward her hardening crotch.

And then, just as a particularly throaty moan slipped from Luna’s lips, they began to grow.

Celestia was the first, if only by a few seconds. One moment, she was “simply” a larger-than-life alicorn, a foot taller than her sister—and then the next, she was looking down at a mare who had to be nearly two feet shorter.

Twilight gaped as Celestia pulled her mouth away and groaned, stretching her long legs to their full length as her growth began. A tear appeared down the side of her dress, then another, and then a third; in what seemed like no time at all, the entire front of her dress had ri-i-i-iped right down the middle, exposing her burgeoning cleavage. Celestia moaned again, her hips jerking against Luna’s. The motion pushed her waist forward and her chest back, causing the top of her dress to tear even further. Her “girls,” now hanging down past the top of her torso, wobbled happily, straining against the tight fabric to a maximum.

But she wasn’t the only one growing. Luna had started too, and was fast catching up. The popping of fibers filled the air as Luna’s big, growing rump forced its way out of its cloth prison. Her pants all but exploded off of her frame as her body climbed higher and higher, her big, jiggly ass cheeks wobbling crazily. Luna was panting, her cheeks burning a bright leg as she thrust her shaft between her and her sister’s jugs again and again, a steady geyser of pre spurting from her erection. As Celestia reached thirteen feet, Luna had just passed twelve—and both sisters looked ready to more than continue growing.

Twilight bit her lip and groaned. All of the heat in her body seemed to be rushing to her crotch. Her shaft pushed mightily against her pant leg, swelling with approval at the sight of the two growing princesses. It still wasn’t sure what it was seeing, but whatever it was, it liked it.

She didn’t even come up to Luna’s shoulders anymore; the top of her head would have just barely brushed against the bottoms of Celestia’s magnificent breasts. She struggled to close her eyes, but she just couldn’t look away. She could already feel her blood pounding in her ears, her breasts straining against her shirt as her own body yearned to join in the princess’ dance of growth.

No, she would’ve told herself a day ago. I can’t. But today… She watched her growing mentor with barely concealed lust and fascination. Today, she couldn’t help but feel as though her entire world had been turned on its head.

Celestia and Luna’s growth was slowing now; both were tapering out at a size that Twilight’s rational mind could estimate at around eighteen feet. Both were just over twice as large as she was, with genitals and bust sizes grown to match. Twilight doubted she’d even come up to Celestia’s waist anymore.

Celestia hungrily dug her fingers into Luna’s rear, her sister’s assflesh spilling through her grasp as she pushed her to the floor. Luna eagerly suckled on the side of Celestia’s neck, the latter gasping and moaning as Luna’s shaft, now towering above both of their heads, continued to erupt with precum. Twilight watched Luna’s crotch with awe, the lunar princess’ titanic balls swelling up with incalculable volumes of seed as they pushed her legs apart. Celestia’s own plump, round nuts sat on top of them, slightly smaller, but no less virile. The two princess’ moaned, grinding against one another, their stallionhoods slapping madly against one another as they grew and grew and grew. Twilight was nearly at her breaking point.

And then Celestia glanced back at her and winked. Twilight’s tentative control shattered.

As the first tendrils of growth snaked through her limbs, Twilight realized that she wasn’t feeling entirely out of control. No: she wanted this. Wanted to feel what Celestia and Luna were feeling. And her body responded to that desire in spades.

In the blink of an eye, she’d increased her size by nearly half. Her clothes snapped and popped around her big, growing body. Her shirt and pants gave out together, her jigs breaking free at the same time that her ass split her pants right down the seams. Twilight let out a cry of pleasure as her shaft, now nearly the length of her leg and still growing, ripped its way out of her pants. It bobbed up to rest between her cleavage, irregular globs of pre as wide around as her fist spurting out with her every breath.

Twilight grunted, her arms thickening, muscles tightening, legs widening. Her thighs pushed together as her balls weighed lower and lower. She felt the seed building up inside of them, the pressure building until she felt like a dam ready to burst.

Her body continued to grow, adding on another few feet in height. She was just barely shorter than Celestia now; her head would have just barely reached the giant Princess’ chin. As her growth tapered off with a few extra inches of size, Twilight groaned, feeling the pressure in her balls mounting even higher. She could feel them sloshing between her legs, gallons and gallons of seed building within them until there was nowhere to go but out.

She cried out, her whole body jerking madly as she hit her peak. Twilight’s back arched over her rear, thrusting her breasts forward around her shaft. It stretched above her by a good foot and a half now, her beanbag chair-sized balls plump and heavy between her legs, dropping down nearly to her shins. Huffing, moaning, and twisting, Twilight came a flood.

An ocean of white burst from her tip: thick, creamy baby batter that erupted from a bulge just beneath her flare. Wave after wave of her musky seed splattered against the walls, the floor, the ceiling—even the other princesses—as Twilight collapsed to the floor, her cum-bloated nutsack squishing gently between her knees. Her hips jerked wildly as she came, her every load easily dozens of gallons in volume. Thick globs of her seed soon covered every inch of the blast zone, rolling down the walls and collecting in huge pools on the tiles.

When Twilight emerged from her post-orgasm haze, the first thing she heard was clapping.

Princess Celestia was smiling. “Very nice, Twilight,” she said. “You look wonderful.”

“Indeed,” Luna said. Her eyes were glittering mischievously. “It has been a long while since I have seen another mare as well-proportioned as you.”

Twilight flushed and glanced down at herself. The first thing she noticed was that her orgasm hadn’t caused her size to go down—if anything, her big body seemed bigger and more solid than any other time before. As her eyes roved hungrily over her figure, she took truly took it in for the first time.

She was big everywhere. Her thick, chunky thighs rubbed against one another, forming a soft, curved surface for her massive, plump balls. Even now, after that explosive orgasm, they still felt fat and heavy on her thighs. Twilight bit her lip, her fingers and palm carefully cupping around the side of one of her testicles. She could scarcely believe how big they were.

Her shaft, a monstrous slab of meat longer than she was tall, protruded far in front of her. It was incredibly, impossibly thick, and rested comfortably atop her swollen nutsack. It was drooling a steady mix of precum and jizz, more and more pooling on the marble floor by the second.

Her breasts were enormous; Twilight was comfortably an S-cup, with each massive tit over half as wide as an average pony was tall. They went down nearly to her waist, their sheer weight nearly pulling her back forward. Each of her nipples was larger than a normal pony’s fist, and were achingly, quiveringly stiff in the cool Palace air.

But the rest of her body was more than big—and more than strong—enough to handle her bust. Twilight flexed an arm in awe, watching her biceps bulge out larger than her own head. She was massive—and, she noted, running her fingers over a belly so sculpted that it felt like a row of steel ribbing, built like a tank.

Well, she amended, glancing back over her shoulder. Not quite. Her massive butt jutted out a good four feet behind her tapered waist. Her hips were more than just foalbearing: they stuck out around her with a radius that even Applejack would have been awestruck to so. She bit her lip, lightly tapped one of her globular ass cheeks. A wave of pleasure swept through her, and she nearly lost herself in sensation as her rump jiggled and wobbled madly, her globes of fat assflesh rippling with hundreds of tiny waves.

She glanced up at the ceiling. Even when she was down on her knees like this, she was still a few feet taller than she’d been that morning. Her breath caught in her chest as her proportions really sunk in. She was huge.

That was when she felt a warm pressure on her back, soft fingers trailing their way down her shoulders and down her shoulder blades. Twilight shivered as she felt a rush of hot air against her ear. “It seems so much smaller,” Celestia’s voice murmured, “doesn’t it?”

Twilight’s hands mindlessly moved to massage her balls as Celestia’s snaked their way beneath her armpits. Twilight moaned, her balls throbbing with sudden fullness as Celestia pressed against her back, her arms curving beneath Twilight’s massive bust.

Celestia’s teeth nipped against Twilight’s ear. Twilight groaned as Celestia pinched her nipples playfully, setting her incredible bust jiggling as hard as her ass. “Doesn’t it feel amazing?” Celestia whispered playfully.

“Ooh,” Twilight groaned. “Yessss…”

Her pleasure was only intensified when she felt somepony else suckling on the tip of her shaft. Twilight’s eyes fluttered open. Luna’s lips had latched lightly onto Twilight’s massive flare, her mouth just barely wide enough to cover her massive cockslit. A moan slipped from Twilight’s lips as Luna gulped down the steady stream of her precum, Luna’s own soft, massive tits rubbing against the sides of Twilight’s shaft.

Luna’s own member bobbed gently beside Twilight’s, their thick, veiny surfaces frotting as Twilight’s hips twitched and jerked. Luna may have been a few inches taller, but Twilight’s stallionhood was still a bit larger than hers, her balls bigger and plumper.

Meanwhile, she could also feel the base of Celestia’s shaft against her rump, the solar princess’ jugs surrounding her own shaft and squishing into the curve of Twilight’s back, their radius running all the way from her shoulders down to the curve of her hips. Twilight’s erection was throbbing madly now, more and more precum leaking from her drooling tip. Luna lapped it all up, gulping it down eagerly, her eyes never flickering away from Twilight’s.

“I’ve waited quite a long time for you to join me at this size, my dear student,” Celestia murmured. Twilight gave a muffled whimper, her shaft flaring as Celestia continued to molest her tits, even as she lightly humped Twilight’s flabby rear. “I must admit, it’s certainly made you…”

Her breath was hot and moist on Twilight’s ear. Twilight felt the hairs on the back of her neck sticking straight up.

“...irresistible.” Celestia was all but purring now. “Do you think that you’re ready for your new role?” Her voice sounded playful. “I can promise you, my dear student, that it will be quite—“

Her hand slipped down to Twilight’s crotch. Twilight moaned.

“—quite enjoyable.”

At a soft push on the side of her neck, Twilight turned her head. Her lips met Celestia’s before she’d even turned halfway.

Celestia was a surprisingly good kisser. Then again, Twilight admonished herself, perhaps it wasn’t so surprising—she’d had millenia to practice. She let Celestia take control, melting into the kiss as her former mentor’s fingers roved hungrily across her chest. Celestia’s tongue was warm against her own, her lips wet, her touch hot and electric.

Twilight could feel it again now: a stirring, a heat in her chest. She knew what it meant. The sensation, the pressure of growth continued to build in her gut, swelling up inside of her until—

Didn’t this feel good?

—on impulse, her mind clouded by lust—

Didn’t she want more?

—she gave into it once more.

Instantly, her body surged upward. In a second, she was as big as the other princesses—in another, bigger. Limbs lengthened, muscle fibers swelling and thickening as Twilight’s body pushed upward and outward in every way possible.

Soon, Celestia found her arms being pushed apart by the widening breadth of Twilight’s shoulders, her former student’s butt widening and pushing against her own crotch. On her other side, Luna found herself nearly gagging as a wad of precum the size of her head suddenly burst from Twilight’s tip, her shaft growing by the second.

Twilight moaned, the sensations of growth filling her body. Her stallionhood rose up, stiffening, lengthening, thickening. It managed to wedge itself between her breasts, her monumental tits adding on more and more padding by the second; soon, her bust had swallowed up even her pillar of meat, covering the bottom half entirely and leaving the top half to tower above her chest and head.

Another spurt of pre bubbled from her tip, a steady river flowing down Twilight’s shaft. She squirmed in delight, squeezing her massive tits and letting lakes of titflesh ooze through space between her fingers. Her self-fondling only increased as she pushed past twenty-five feet, her nipples now horribly, achingly stiff. She found herself jerking her hips forward, titfucking herself madly as more and more pre shot up into the air.

Her balls grew fuller and plumper, fat with untold gallons of spooge. Her massive ass continued to grow as well, folding over the tops of her thighs and coming to rest on her quads. Twilight grunted as she pounded her own tits; they already reached below her navel, and were already beginning to brush against the tops of her truly massive nuts. As another growth spurt hit her, sending her shooting up in height until she was at least twice the size of Celestia, she could actually feel her enormous breasts resting on the top of her nuts, the soft, pillowy flesh parting over the base of her shaft and sagging atop her overfilled cum-buckets.

Thrust rudely back by Twilight’s growing ass, Celestia’s let out a choked cry and tumbled backwards. Her own shaft slapped against the floor with a meaty smack, inducing a messy, oversized load from Celestia’s own balls. Part of Twilight’s mind ached for that same release, but somehow, she knew that she was nowhere near finished.

The throne room was an absolutely enormous piece of architecture; yet, Twilight’s growing form seemed to be bringing that into question. On her knees, her head reached up over a third of the way to the ceiling; she had to be nearing forty feet now, and seemed to have no intention of stopping. She squeezed her breasts to her chest, the sudden pressure around her shaft sending a rush of endorphins to her brain. Twilight groaned out in pleasure, huge spurts of precum erupting from her shaft and splattering against the walls and ceiling.

By now, Luna had managed to clamber to her feet, her eyes wide as she stared up at Twilight’s magnificent form. Peeking just over the top of her bust, Twilight managed to make out the other princess’ increasingly tiny form—she only came up to Twilight’s waist now, and if she’d been standing up, it was clear that Twilight’s thigh alone would have towered above the diminutive lunar princess’ head.

A huge spurt of pre burst from Twilight’s tip, splattering against and utterly ruining a tapestry on the far wall. Twilight’s chest heaved, her mind awash in size and power. She thought she’d been big before, but this—this was unlike anything she could have ever imagined. It was like a drug: the bigger she grew, the bigger she wanted to get. And she wasn’t sure how big she could get, but there was no doubt that she wanted to find out.

It was a rush unlike anything she’d ever experienced, a combination of lust, power, and pleasure that mixed into a perfect cocktail of size and arousal. And Twilight loved it, adored it, savored it, drawing it out as far as she could and then letting it flood through her again.

Passing seventy feet in height, she was fast approaching the throne room’s ceiling. Both Celestia and Luna would wouldn’t have been even twice the size of one of her feet. A sudden growth spurt settled that, Twilight’s size nearly doubling, passing one hundred feet, her massive, wriggling feet now each as big as a fully grown alicorn.

The throne room was getting very, very cramped. Even on her knees and pressed against one side of the room, Twilight was still managing to fill most of it. Her cock, almost twice her height, was brushing against the opposite wall, a steady flood of precum drooling from the tip and pooling into a milky-white lake below it. Her huge ass folded over her thighs, smushing against the back wall. It had to be at least three times wider than her waist, her hips widening until “foalbearing” almost seemed an insult. She not only filled up most of the room lengthwise; she filled up most of it breadthwiseas well.

Twilight couldn’t even see Celestia or Luna anymore. Her vision, by now, had become entirely filled up by her own breasts and shaft, not to mention the ceiling that was rapidly rushing down toward her. She felt a sudden weight atop her massive backside, smushed between her wobbling rear and the wall, and wondered if that was Celestia. The thought of crushing her mentor with her bulk, of being so much bigger than not only Celestia, but the room itself—it turned her on more than anything before.

Reaching between her breasts and balls, Twilight began to fervently stroke her massive pole of meat, which by now had to be even more massive than she was. Her moan filled the room. A final surge of growth washed through her body, pushing her up and outward until the top of her head just barely brushed against the ceiling.

Hunched over, eyes closed, and teeth gritted, Twilight felt the floor begin to shake. An ominous rumbling began to spread throughout the room, then through the palace, as her arousal built to an inescapable peak. She was panting, moaning; Celestia and Luna, lost among her huge, magnificent body, were powerless to do anything as Twilight brought herself to the edge—and went over.

With a cry, she went off. An ocean of cum erupted from her shaft, globs of jizz the size of wagoncarts spurting out. Those were the only the heralds of a much larger eruption, though; as Twilight’s cry twisted into a moan of impossible pleasure, a flood of seed bulged upward from Twilight’s balls before releasing directly into the throne room.

It flooded through the door, less a collection of spurts than a single, impossibly large load. Each of Twilight’s “spurts,” barely distinguishable from the others, carried hundreds or even thousands of gallons of cum. Her massive load rose up a good five feet of the throne room before shattering the doors, the pressure of thousands of gallons of her seed too much for them to withstand.

Her enormous balls, each the size of a small house, continued to empty themselves into the palace, flooding first this wing, then the rest of the structure as more and more seed burst from her shaft. Twilight howled, her chest heaving around her tool as more and more of her seed filled the palace, power and heat rippling through her body as she came.

More and more of her seed ripped through the doors, her balls churning, her shaft lurching. An ocean of spooge was filling the palace, Twilight’s monstrous size coming to dominate not only the throne room, but all of Canterlot Palace as well.

Then she felt it: her balls, swelling up to incredible sizes, readying themselves for one final, massive load. Twilight’s breath caught in her chest, her head turning upwards, her horn cracking the ceiling as her stallionhood bulged to twice its width, getting ready to unleash an impossible amount of seed—

With a moan, Twilight passed out.

When she awoke, it was to Celestia’s serene, smiling face.

Twilight groaned. Her head hurt. Wait; scratch that—her everything hurt. She felt sore all over. At the same time, she’d never felt quite so good, either. A warm afterglow had spread throughout her entire body, with warm, fuzzy tingles swirling through her bloodstream.

She groaned again, lifted a hand to her forehead. “Ce..Celestia?”

“Yes, Twilight.” A normal-sized Celestia smiled down at her. She was cradling Twilight’s head in her arms, the other mare’s neck resting in her lap. “Are you alright?”

“I… think.” Twilight grunted, pulling herself up. She blinked around at her surroundings as she slowly returned to lucidity.

“Um,” she said dumbly. “Wow.” The entire room was coated in a thick coat of white. Fat globs of cum rolled down the spooge-covered walls. Though it, too was splattered with seed, the dais of Celestia’s throne was an island refuge above the two-foot sea of Twilight’s cum that still covered the rest of the floor.

“You, ah, left a bit of a mess,” Celestia said.

“I can see that.” Twilight groaned. She could make out the crater-shaped (and -sized) indentations on the walls and ceiling where both her heads—she tiredly snickered at her own pun—had crashed against their surfaces.

Luna came up behind her and set her arms on Twilight’s shoulders. Twilight glanced up and saw that Luna’s face was drenched in her thick, white cream. Luna licked it up with a satisfying slurp. “A most delicious one at that. And,” she added, “an astounding one. I’ve never seen a pony with that much raw power.”

“She unleashed it all,” Celestia said, softly stroking Twilight’s hair. “We should have expected something that big. All in all,” she said, shrugging, “a good start.”

“A good...start?” Twilight blinked, her mind swimming. “Start to what?”

Celestia just smiled. “Well,” she said, “It was very impressive. But—“ she held up a finger, a soft smirk on her face—“You can do better.

“And,” she added, after a moment, “bigger.”

“Oh,” Twilight said. “Good.” She took a deep breath—and then passed out again in Celestia’s arms.

There was a smile on her face.