Somewhere on Mobius...

Tucked deep away in a hidden remote corner of the world, was a small and private little place... Unassuming from the outside, with a view of a beautiful beach, and surrounded by tall trees of the most luscious emerald green. Parked outside was an impressive red bi-plane, unused for a time since its usual passangers were all busy with their own adventures, but its construction and maintenance told that its owner was a highly advanced type who was eager to explore the unknown...
Inside the small hut, past the front door and the quaint living area that had stacks of documents or half deconstructed mechanical pieces on every surface, was a metal door. And beyond that door, and the sophisticated security system that guarded it, was a stairway down to a series of rooms larger all together than the living quarters above... Metal walls polished to an iron glimmer, tile floor, and a cascade of machines and workbenches; a somewhat disorganized pile of metal golden rings... A half deconstructed robotic ladybird... And at the last table, a frothing canister of luminous liquid, swirling and seemingly attempting to collesce into a pointed gemstone shape, but was too chaotic to fully come together...
Miles stood in front of it, his hand cupping his chin as he took a moment from his intense research to merely contemplate; it had been months since anyone had gotten up to anything that put the world in danger. Without needing to go about saving, the heroes who usually kept order were first relaxed... then bored... then restless. Now, even the grounded and intelligent 'Tails' was pushing on boundries he shouldn't. A certain other hedgehog was desperate for a kid with her husband, (though whether he truly was her husband or she was simply making future plans...), and Tails had been unstimulated enough to take her request in earnest. He was, however, an engineer, and was much less of a doctor. Unfortunately for him, the only doctor he knew was... not an ideal option, to put it simply. So he had tinkered and experimented himself, until...
He really wasn't supposed to be using such immense energy for such mundane tasks. These ancient gemstones were too powerful to futz about with for anything less than world changing implications. But here he was, trying to stir the pot in just such a way as to get a fertility potion, as if he was some ancient alchemist instead of one of the best scientists on Mobius...
He reached forward and tapped the glass. He could swear for a moment that the cloudy liquid formed the image of a baby bottle in it before again, its contents swirled and thumped against the side of the glass, almost violently dispersing from their center point...
"Well..." he muttered to himself, still rubbing the furry tufts about his somewhat childish face... Despite growing much older than when he first began his adventures long ago, he was still 'the baby' of the group. It weighed on him, that he wasn't often taken seriously. One could say that he was feeling a bit emasculated too, given this experiment was a request from a girl to get closer to HIS best friend... The two tailed fox put his hands firmly on his hips and sighed... "It isn't really doing much... It's reacting, but Chaos Energy always reacts to the environment around it. If only there was a way to understand how the ancient people kept this force contained, compressed into gemstones even...."
He didn't have access to the Emeralds at the moment. He knew their keeper... Hell, he even knew the guy who kept the MASTER Emerald. But for this experiment, a shard of one's power would do. Indeed, the small canister had nothing but a sliver of material to decant, and yet...
The cloudly liquid compressed, and then slammed against the walls of its prison again. Tails jumped a little as hazy, natal themed imagery was formed and dispersed repeatedly...
"If I didn't know better, I'd say this liquid was..."
The milky white fluid compressed tightly into a point so small that even Tails had a moment of confusion, thinking it had disappeared. Then it expanded rapidly and smashed through the glass, bursting as if there had been a bomb within it. Tails let out a startled yell as the liquid splattered on the walls behind him, around him, but mostly ON him...
"Ahh... Geez." he huffed to himself, once he'd patted along his fur to make sure he hadn't gotten injured at all. He didn't notice the liquid seeping inside and disappearing until he was halfway across the lab in a slightly panicked jog... He worked with some strong chemicals even as an engineer, so luckily he had built a small decontamination room nearby. His tension and need to rush had him hop up, his tails spinning like a high powered fan to propel  him foward faster than his little legs could carry...
Only... His shoes dragged along the floor. He was flying low. He wasn't sure why, but landed with a wobble near the door and pulled it open. Stepping inside, it seemed almost like a normal shower, albeit hooked into a water supply that was full of cleansing soaps and chemicals... He took the time to remove what meager clothing he wore, which was typical for a Mobian like him... But for some reason, stripping down 'naked' was making him feel... funny. Physically, he noticed that bending and twisting his body to pull his shoes off was putting odd pressure on his back... his hips...
"That Chaos energy shouldn't have done anything to me..." he said, looking at his hands, then his body. He was lying to himself, and he knew it... Especially with the ingredients and modifications he had made, he knew that such potent energy would indeed have effects... But given it was meant for females who wanted to have kids... and the fact that it was CHAOS energy... Well, he was left damningly unaware...
He heard his stomach gurgle in an almost pleasant way. He rubbed his finger on the nipple hidden below his fur, and winced hard... Why were they so sensitive...? Perhaps he was just stressed, or so he nervously told himself... And he realized he'd delayed turning the water on. In a moment, it became too late to matter...
Like a lightning bolt in reverse, a wave of sensation started low in his body and then rushed up his spine, twisting through his brain and making him see stars. It started when another pain in his hips spread upwards, causing immense heat in his stomach and immense pressure behind his pecs. His attempts to swallow were blocked as his throat tightened, and the soft squeak he made was higher pitched even than his regular voice... And then it hit his mind, and he swore that as his nose twitched, he could smell baby powder and hear a soft crinkling...
He thumped his head against the tile, his back flat to it and his hands splayed on it near his hips. He trembled and slid down to a sit. Strangely, he knew he wasn't going to be hurt by this accident... Perhaps that was the energy itself in his brain, relaxing and reassuring him. Or perhaps it was the fact that everywhere the energy seemed to curl, it was sparking the most intense sensations of pleasure instead of worrying pain... Oh, there was still pain underneath, but it was mild... And almost made things better...
"Ah...?!" he gasped, as he had caught a glimpse of himself. His fur was puffed on end, but even that couldn't prevent him from seeing that his chest was swelling... It seemed with each heartbeat, they stretched out a little more, swelling like waterballoons as he watched. They weren't the only things either; his hips pushed outwards, muscling their way past the will of the muscles and flesh to force a new shape; one wider and rounder than it had been before. Even the puffy fur seemed smoother, silkier, and in places like around his head, longer...
"Oh no...!" he whimpered, feeling along himself... which quickly turned into feeling along his growing assets and moaning in such a lewd way that he was caught off guard that it had come from his own muzzle... His white furry cheeks were flushed, and his dexterious inventor's fingers slipped along his breasts, his fattened thighs, his much heavier backside...
"What... the..." he muttered, as he felt between his legs. He expected that to be smaller, perhaps even receded enough to be a puffy slit instead. But his hand curled almost sheepishly around a fully erect member that had been there before... THAT at least was the same, albeit hard enough that it was almost painful... But that might not have been a side effect so much as...
He blushed deeper and stood on his knees again. He reached up carefully and turned the water valve until pleasantly warm water splattered against his furry body, soaking it and giving it a luxurious sheen. But it did absolutely nothing to reverse the now nearly throbbing sensitivity of his new self...
"But..." he huffed, flabberghasted at all that had happened so quickly. He attempted to stand from his kneel... But doubled over instead, eyes huge...
His insides had just groaned, louder than a ship scraping the dock. He pulled back and settled on his knees, staring downwards...
Why was his belly puffy too...?
"Uh oh."
In the span of a mere minute, he got to watch as his fluffy white belly fur, matted and slick with water, pushed out in all directions. Soon it became obvious that it wasn't just pudge, and instead took on the telltale roundness that his 'client' that had requested the formula in the first place jealously chased after. Stretching, perhaps making sounds like an inflating balloon albeit that was almost certainly just been Tail's imagination, he watched as his body went from masculine, to utterly feminine besides his sex, to utterly feminine besides his sex and swollen pregnant middle, and then to full term...
He felt the urge to call for help. He knew if he was in the field he'd be knelt, surrounded by scattered rings, and begging for a checkpoint to restart. He knew what was coming, after all, and he was panicking enough that he couldn't focus on a way to stop it...
Instead, with a sharp twinge, he knew it was only getting started.
He arched and squealed, gripping his backside. He thought he felt a gush of fluid, but he wasn't sure. Either way, the slick port that was below his twin tails was bulging, puffy, and dribbling. He breathed faster as he thought that he had to stand, get out of the shower, go to his phone, call someone... ANYONE! Even the doctor he had discarded, so long as they were a doctor!!!
But despite the internal pressure, the twinges of pain, the fact that his hips felt like they would split... There was a fire in his newly swelled midsection. He placed his hands tightly on it and breathed, irregularly admittedly, as he felt SOMETHING move inside him... He gripped his ass again and set his jaw, pursing his lips in pain, while ignoring how his own belly was bumping firmly against his visibly throbbing erection...
He couldn't take it anymore... He fell to all fours, intending to stand, but he simply couldn't command his body to move. Instead, IT demanded something of HIM... and he would oblige it or he would sit here in pain...
He pushed. He couldn't believe what he was doing, but he pushed... On all fours, his belly sagging and swaying, his tits soapy and wet, he gritted his fangs and pushed as hard as he could. Just minutes ago, he was Mobius's prime scientist, and now he was reduced to moaning as he felt the pressure stretch his passage... He would be ruined after this... And that thought cascaded out until he realized he was worried about being too ruined to take a male, and have another...
His breath steamed up the glass door near to him. His eyes rolled back, and he reveled in the feeling. It hurt, for certain, but whether because the energy warped his body that far... or the sensations were just genuinly thrilling to the strange fox, who could say? The practical difference was nil; he still wobbled there on all fours, pushing and moaning, reaching back to touch at his tailhole to find it bulging... And then one time, with a burning sensation, he found that there was a furry head peeking just out of his new 'folds'...
"Oh my god...!" he gasped, upon realizing that yes indeed, he was really doing it... He was giving birth. His member still throbbed and threatened to coat the floor below with the proof of his malehood... But the proof of his femalehood was slamming at his backdoor, demanding out, so he could start his maternal journey anew...
He pushed. His paws curled to fists and he lowered his head to push into them as he concentrated. He whimpered as his tails lifted and spun lazily, spattering water everywhere as his firstborn stretched him... Further... Further... He had to reach back with one hand and pull his cheeks apart...
He squealed again. He had to maintain the push to make sure the head didn't slip back. Harder and harder he was pulled apart by the sheer weight of his baby, until it reached a point where...
Pop!
With a gasp, Tails thumped his head back down and took a break. On all fours, not moving, he had his firstborn's head dangling from his backside. He groaned and pushed himself up to a squat on his knees, moving his hands between his thighs to catch as he pushed a few more times, and a furry little fox body slid out and into his arms...
He laid there in the gentle drizzle of warm water, panting hard. His baby clutched to his chest knew better what to do in this situation than he did; latching on to his newly grown ample breast and taking its fill eagerly. Tails shuddered and looked at himself... Slick with water, belly still baby fattened, and his figure 'ruined'... Would he even be able to fly with an ass that thick? He'd have to learn... The changes seemed to show no sign of reversing... And his belly already subtly tingled with desire to fix its emptiness...
He blushed at the very musing and held his kid tighter...
"Guess my formula was a complete success... I'll never hear the end of this from Sonic..."

-The End