The Story
“Do you think anypony saw us?” asked Dash as she peaked out around the corner. Her gaze went back and forth sharply, looking for anypony or anyone at all who was looking her way too long. Luckily, nopony seemed to have noticed the pair of ponies walking along the streets. But why should they? After all, both of them had been living in Ponyville for years, so it wasn't unusual for them to be seen walking the streets.
“Dashie, Dashie, Dashie. You should stop worrying too much before you turn into a pseudo Twilight. This is just a little OoC stuff we're going to do. I mean, it’s not like this is going to affect the canon,” said Pinkie, smiling at her friend.
Rainbow Dash, looking at the pink earth pony like she was nuts, just shook her head and followed, ducking quickly into Sugar Cube Corner. The two of them were alone, with the Cakes, all four of them heading towards Canterlot to make a special delivery and Pinkie had, at Dash's request, let the store close early. As Celestia's sun waned in the sky, they found the place empty, and the pegasus quickly shot up the stairs to the living quarters, followed closely by a bouncing Pinkie.
“So, you're sure this is gonna work?” asked Dash as she settled back down onto the wood floor.
The earth pony soon bounced to a stop next to her and opened her room, pushing on a special place next to her, which in turn caused the thing to flip upward, revealing a flat blank wall. She then hopped up and pushed on the door knob, which caused the door to swing open, revealing a room that appeared normal as long as you didn’t think too much about how the furniture was just kind of stuck to one wall, with the bed in the upper left corner. Dash, used to Pinkie's ability to warp reality sometimes, just rolled with it, flying up into the room and nearly flopping as down became sideways and sideways became down, all while Pinkie gently walked up the wall.
“Of course I'm sure silly. You pegasi are lighter than air, otherwise you couldn't fly, so all we have to do is put more air in you, and then you'll be even lighter. Plus, bigger wings mean bigger power behind them,” she said with a giggle as she walked to a wall in her room that should be the ceiling before she started to dig inside a chest. Out of said chest came a green watch thing, a green ring and then a golden thing that looked like those 'hands' Lyra was always going on about, but this one was set with several gems.
Pinkie Pie listed each item as she took them out of the chest. “Omnitrix, Green Lantern Ring, Infinity Gauntlet, AHA! Here we go. One good old fashioned bicycle pump!” declared the pony as she finally pulled out something normal.
“Um, I just thought about this, but where are you planning on sticking that?” asked Dash, a bit worried, not for the first time, since Pinkie suggested this was a way to make her faster. Without thinking about it, her wings folded in such a way that completely covered her plot as Pinkie walked right up to her.
“Heh, well, I think we should probably stick it in your mouth. This is going to be a kinky story, but at least this way everypony can read it.” And with that, she stuffed the end of the air hose into Rainbow Dash's mouth. Dash tried to speak through the rubber and metal between her lips, but before she could voice any objections, Pinkie started pumping.
Little bulges quickly appeared in the hose before being pushed upwards, and they soon found their way towards Rainbow Dash’s mouth. She had expected, of course, that the process would feel like she was gulping down lumps, but instead it felt... weirder. Like they were somehow being absorbed into her body, but that couldn’t be possible. Rather than being swallowed, the things just spread all over her body, making her fur, mane and skin tingle a little before they started to grow. Each lump pushed her farther apart from where she had been, expanding her body as she found herself unable to move. Her hooves slid across the floor, making a scraping noise so loud that made her wish she could cover her ears.
The growth was gradual at first. Every lump of air was a centimeter or two at a time, but every one of them seemed to go up, exponentially increasing the next. Soon, what had been centimeters was instead decimeters, making each growth bigger than the last one. Oddly enough, she didn't feel any pain or anything like that. She'd expected it to feel like she was pulling on her skin or something similar to expanding like rubber; instead, it was just like everything else was shrinking. Of course, she soon ran into a little problem with her growth spurts.
That problem was that she was in a house, or rather a bakery. Whatever it was, she was inside, and as she grew larger and larger, soon doubling in size and still going up from there, she found the ceiling... wall... whatever it was, banging against her head as she continued to expand. But Pinkie seemed oblivious to this, and just continued pumping. Rainbow tried to spit the end of the hose out at this point, figuring she was big enough, but Pinkie had done something to it, or maybe it was a special hose, because she found it impossible to do anything other than hold it between her clenched teeth as she grew larger, and bigger, and giant.
Soon she was cramped into a near fetal position, as her body had to curl together to keep from breaking the walls apart, the floor creaking, and the whole building shuddering as her growth continued unabated. Rainbow felt like she was in a vice, and mentally begged Pinkie to stop. The earth pony seemed to pause for a moment, looking her in the eye before giving Rainbow Dash a rather mischievous smile as she redoubled her pumping, making Dash's expansions come even quicker.
All at once, something gave in. Luckily for Dash, it was the house rather than her body. First, the floor under her finally snapped, unable to hold her weight as she crashed against the bottom floor. Unfortunately, her problems of space didn’t stop, as Pinkie Pie continued to pump her full of air. It didn’t take long before her body covered the entire building, with little lumps trying to escape through the door, windows and any other holes of Sugarcube Corner. Rainbow Dash was worried of being crushed to death, when suddenly, the wall her left rear hoof was pressed against blasted outwards, sending splinters and debris flying everywhere, now feeling less cramped.
Better than that, the roof was the next one to break, her head bursting out slowly with each growth spurt before the walls started to creak, her body pressing against them. In the blink of an eye, the building gave up and Rainbow Dash was freed, at last able to stand up again as a titan looking down at Ponyville standing on all of her hooves. The room and the whole bakery were trashed of course, but as she stood there, looking down, she realized she was going to have worse problems. Her hooves were now larger than the ponies around her, and she had to sheepishly set one down gently to avoid crushing some gray mare and her brown earth pony companion.
Yet Pinkie didn't stop, even as Rainbow Dash's hooves grew larger than houses, pushing them aside as everypony tried to run away, scared of the giant rainbow pegasus. The cyan mare, panicking, started to flap her wings quickly, trying to launch herself high into the sky. Unfortunately, she was so big now that while she was probably covering the entire town, yet Pinkie still didn't stop, her pumping becoming even more frantic.
Dash realized after a few minutes that she was even taller than Canterlot, and yet her head kept going higher, even as she tried to beat her wings as gently as possible to avoid a hurricane at those tiny specks on the ground. She saw, out of the corner of her eye, several such specks buzzing around her, like very tiny bugs that had a distinct blue hue to them, and she realized with shock they were the Wonderbolts. They seemed to not want to hurt her either, because instead of blasting her or hammering into her with their hooves, like she expected, Rainbow Dash found them pushing her body upwards, their combined wing power helping her ascend higher, and higher and higher.
When at last they stopped, her head was at the same level with Cloudsdale, and yet, nothing seemed to slow Pinkie, who was now standing on her lip as a single pink crumb that kept pumping. Rainbow Dash had to go higher still, her legs about to crush the entirety of Ponyville beneath her mighty hoof. So she raised again, her legs growing so long that even if she had been standing on ground, her eyes would have probably surpassed Cloudsdale.
And then, all at once, Pinkie stopped. Dash felt the growth end, and she was able to take everything it. She suddenly realized that she was floating above a small sphere. Well, small compared to what she knew it was supposed to be. It was still as large as Canterlot palace, but Rainbow Dash realized that this sphere was her planet, her whole world. Her wings blotted out the sun, and she knew that by stretching her hoof, she could be able to touch the moon. Such was her power that if she had landed, she didn't doubt that the impact would have been felt on the other side. That’s when she felt a little tickle in her ear.
“Sorry Sayer, the pump broke, so this is as big as she's getting. Still, I hope you enjoy this,” she heard Pinkie say. Rainbow Dash wondered just who she was talking to, and more importantly what was she going to do about this whole situation. Fortunately for her, down below, three Alicorns got together to find some magical solution to the problem.