“Alright, Colin, preparing for the injection. Last chance to back out now. Are you ready?” Came the familiar voice of his commander over the speaker. Colin nodded, giving a thumbs up toward the small camera in the corner of the chamber. It felt a little like he was being kept in a cell, and in some ways, he was. It was hardly a disagreeable circumstance to be in. He needed to be in a cell in case something went wrong for his own protection or for others. After all, while the serum about to flow into his veins was ‘safe’, or at least as safe as it could be, every precaution was warranted to make sure that nothing ill-fated happened. 

Having been in the military for as long as he was allowed to enlist, Colin naturally had the motivation to work out frequently. Modern military work required less in the way of physical activity and more in the way of technology as humanity moved to explore the galaxy. Still, there was a push towards increasing one’s physical physique to its apex to make up for all of the possible challenges an alien environment might hold. After all, in a life-and-death circumstance, only one’s body could be relied on when technology failed, and the chips were down.

And so, with that in mind, Colin had trained all his life to reach the peak physical ideal for his body. Yet, even with diets, rigorous exercise regiments, and special training, there was nothing Colin could undergo that would bring his body further physical perfection than what he already achieved. To his dismay, his best efforts could not result in a man as fit for the service’s ideal as he always wanted to be. Worst of all, his scrawny stature led to him being passed up for promotion on many occasions, though it was never expressed explicitly as such. Colin knew better, further lamenting his genetics.

So, when the opportunity to join a program that offered direct physical enhancement as part of an experiment, Colin jumped at the chance to sign up even though the warnings for the program were potentially dire. To his delight, he was the first of the volunteers to be selected. Not that such risk turned him off the chance to get the body of his dreams, mind. His lack of hesitation was simply seen as dedicated to the service, thankfully. His true reason for signing up to gain the body of his dreams was more personal in nature. The idea of rapid muscle growth was powerfully arousing, and he would surely experience the orgasm of a lifetime to undergo it in real life. Though it would have been powerfully embarrassing to be seen doing that in front of a lab crew, Colin was sure he wouldn’t be able to hold back and could always blame it on a side effect of the serum in the worst case! And, besides, his personal fixation wouldn’t affect the program’s results, right?

Naturally, he had inquired about the source of the serum, wondering how they came up with the idea and technology for a literal super-solider serum. It was a closely guarded secret, of course, one that only the handful of scientists in the lab had been privy to. Colin didn’t question it too much in the end, however, not caring how they came up with it as long as it had the expected results. Besides, it had to be safe if they were ready to start with human testing. Right?

Still, even if there were risks, Colin was all in and couldn’t imagine backing out now. Sitting in the chamber, he awaited the injection into his skin like a child waiting for Christmas morning. In full hazmat suit, a doctor came in to inject him, and the needle went in and out effortlessly. It was done. Come hell or high water Colin would have to live with the consequences of his choice. And at the moment, he thought any risk was worth it. 

“Alright, Colin, monitoring your systems. Everything looks normal. Might take a while to-wait. Something’s happening. Already?” Came the voice on the speaker, and Colin felt a shiver running through him. Was it really to happen already? It was too exciting!

The tingling that started in his upper arms was all the proof he needed to know that the process was working. It began around the injection site, ripples running through his chest and down his hand. It was numb, though not painfully so, not indicative he was having a heart attack or the like. Rather, he felt equally powerful and delighted, not just from the beginnings of the changes themselves but from the implications of what they would do to him. 

Burning into his muscles now, Colin was shocked to feel the tissues twitching, writhing almost irritatingly against the skin as they soon outgrew its contours. It felt as though his skin would tear from the force of growth, though his dermis soon stretched to keep up, the stretch marks spreading across the skin only long enough to allow the muscle to settle. Within moments, the muscle had bulked up beyond anything his years of working out could manage, tone starting to show under the skin looking just like he had always imagined. It was really working!

Soon, the dips and peaks of his muscles were obvious, both arms growing in tandem now so as not to look out of place. His biceps, triceps, deltoids, and all the muscles were being stretched and pulled and torn apart painlessly. Only a mild ache proceeded the changes, not at all like the tearing and pains of gym gains he had been used to. It soon came to the point that the meat was appearing to bubble and writhe under the skin, forming the definition of firm-packed muscle he always craved to see on his frame. Rubbing their contours in elation, Colin felt himself almost pound erect, the outset of the change more than he could have ever hoped for. And he was sure it was only the beginning!

The dull ache felt from his pecs pulling against the skin prompted his hands to move to them, the bare skin tugging against the force of it before remolding for the muscle underneath. They were pulled taut and beyond, the tears and reformations so fast that Colin was barely aware of it. Already flat, their width and length soon stretched almost off his frame, though he was still deftly able to move arms that were objectively beefier than some of the largest jocks in the service. Soon his clothes started to tighten from either side, his uniform not made for something the size he was becoming. Did the designers of the formula know how large he was projected to get? Would he rip out of his clothes? Colin sure hoped so!

His chest, too, started to swell, thickening steadily all the way down toward his flat belly, which itself was bubbling from the formation of what had to be well-defined abs. Exploratory hands were rubbing all over it as his stretched stomach pulled upward, likely adding an inch and then two to his overall height. It was easy for him to see in real-time as his shirt was pulled slightly upward, allowing an accurate way to measure his progress. It was exciting to think of all the changes to his life now, like an entirely new wardrobe to fit his larger stature!

By this point, both of his arms were more or less uniform in their new state, and with his larger upper body looked almost cartoonishly oversized compared to his legs, making him sure if he tried to stand, such would be painful. Though it was soon to change, the tingling soreness of transformation and heat working into his thighs and hips, expanding them to impossible proportions within his pants and bringing them almost painfully against the skin. The actual growth was comfortable, though the ache against his clothing caused by the sudden expansion was not. He would surely have to rip out of them in order to free himself, though that realization left him more excited than anything. In fact, his clothing felt tight all over, making it hard for him to breathe as they tautened further, calves and thighs the latest muscles to press against his work uniform.

It was more than mere muscle growth that was changing in his frame. Hands were getting larger as he flexed the fingers, digits fattened into that of a man far beyond his stature. Feet were tight in his boots, Colin resisting the urges to twitch the digits since he lacked the space to do so. He wanted to kick them off, but with the tightness in his clothing, it was harder to bend down in his chair. With some effort, Colin tried to get up, dizzy from the change in stature and the smaller contours of the room. Had he grown so much already? It was already beyond anything he could have imagined. And the tingling seemed not to be done with him yet!

The alterations to his form should have been much slower, and the distant sounds of his coworkers discussing such over the coms were confirmation of that. He wasn’t sure exactly how large the endgame of the serum would make him. He was already the man of his dreams, so to speak, with the size he had obtained. Flexing his muscles caused tears to run up the sleeves, back muscles bulging from the effort and bringing the clothing precariously toward the breaking point. Trying to bend down to take off his boots sent tearing through the pants covering his ass, and for a moment, Colin felt self-conscious. Given that, he opted to stand with his front to the camera while he played with his changing body.  

Rubbing the enlarged muscles of his arms and chest, Colin couldn’t help but get a boner, his rod nearly painfully taut in his pants. The divots and ripples across his skin were amazing, Colin never able to touch such muscle in his life. His abs, exposed under a shirt several sizes too small for himself, were rock hard, hardly the false idols he had been concerned about gaining. It was all genuine muscle, beyond what most bodybuilders could achieve in their wildest imaginations. His building thighs, tight ass, and massive back were all chiseled perfection, almost unnaturally so. Though Colin was remiss to care in the moment of having literally everything he had dreamed about and more. 

With the ache in his cock and the pain of entrapment he was feeling, there was little ability for Colin to resist touching himself, though his larger hands could hardly get the zipper down without tearing off the uniform. A moan escaped his lips, realizing there was no way to get to himself in his current state. Though he was a little ashamed of it, Colin was left rubbing his cock through his pants, the stimulation hardly enough to satisfy his needs but better than nothing. Even the embarrassment of doing so in front of dozens of fellow military officers was hard-pressed to make him care with his needs as high as they were. 

By now, his clothes had reached the breaking point, and it was clear from the persistent tingling it was not stopping. Colin was already so massive, yet it seemed he had not reached his final size. How big was he going to get? The seams on the back of his shirt were starting to tear, popping down the back and exposing his skin and muscles. Pecs were pulling at the fringes of his shirt, and with the pressure of upper arms within taut cuffs, the shirt was not to last on his frame. His belt was near the breaking point, the leather pulled tautly, stretched into fragments due to pull apart with further growth. Pant cuffs were pulled up toward his upper calves, the bottoms tearing as rips ran up towards his thickened thighs. His ass had already broken through the back of his army pants, leaving little doubt his underwear would follow suit. 

Though it was growth from the front end, a leaking cock drooling into his underwear and making it likely that his lancing rod would burst forth from its sheer insistence. It was already larger than he’d ever been, and Colin was no slouch in that department despite his smaller frame. The member he possessed seemed to be at least ten inches and still growing if the tingling sensations were any indication. Whatever the serum had done to him gave him a dick to match his new body, one that he was eager to play with as soon as possible. Colin had to marvel at that last bit of knowledge, not sure why it was part of the process but glad of it nonetheless. 

By this point, his torn clothing was hanging off him, his shirt tearing down the back and split in two. Still rubbing the skin with eagerness, Colin was a little shocked to discover a bizarre texture beyond the human tone he was growing. It was as though the skin was becoming coarse, leathery, nothing close to the consistency he would have expected. Looking back as best he could, Colin was shocked to see a patch of off-colored skin, dark and ashen spreading over the muscles of his back and moving toward his torso. Far too fast to be a rash or infection, Colin was left with the conclusion it was part of the change. But then, what did it mean for what his superiors were really doing to him?!

“What the…?” He managed to choke out, though was not expecting a response. Yet, one came, the speakers coming to life with an explanation. 

“The DNA used for the process was… alien in origin. Compatible with human DNA and able to reform it into a hybrid of the two. All tests showed that it would enhance a host’s own physiology. There was nothing to indicate it would take it over!” The voice came back, and Colin felt his blood grow cold from the revelation. Would they really do something so sinister just to improve the quality of their soldiers? What had they been doing, getting it ready for human testing?

Yet, there was little time to reflect on such with the changes growing in intensity, altering him toward a creature of unknown origin. He hadn’t even known evidence of aliens had been discovered, much less their DNA was flowing through his system, making him larger, more powerful. The force of growth soon did away with his belt, popping it away as the zipper, too, tore from his pants and exposed a musky rush of thick fluids. His ass burst fully from his pants as well, the inseam tearing all the way through to his crotch and further down, leaving nothing to the imagination. No longer embarrassed and eager to see what he could, Colin relinquished himself of the human things, watching as they fell to the floor and left him naked, save for his underwear. 

Despite his horror at what was happening, Colin couldn’t quite let go of his arousal, feeling powerfully conflicted over the source of the changes and their eventual result. He didn’t want to be an alien, but its DNA was giving him the body of his dreams, right? And, besides, Colin had no choice in the matter any longer. Without hesitation, he figured there was nothing to be done for it, save sitting back and enjoying the rest of the changes and what they would eventually do to him. 

The patch of blackening skin was spreading all the while, covering his chest and belly and moving down his legs. It seemed the texture would eventually overtake all of his skin, the sight of it rather ugly, all things considered. But as Colin frantically rubbed the newly grown flesh, the texture of muscle underneath left him elated, knowing that he had much growth left to undergo before the changes were done with him. Was such skin a high price to pay for him to finally be undergoing the change of his dreams? Colin was having an almost impossible time deciding!

A series of cracks in his hand broke Colin’s reflection, and looking down, one of his fingers seemed to shorten, his pinkies losing mass as though dissolving. Within a few seconds, he was no longer able to move them, and as he watched, the rest of his former digits retracted into his palms, not needed on the anatomy of the creature he was becoming. Was he to change all the way into some sort of muscled, alien being? Colin was equal parts terrified and curious to see where the changes would go!

Boots getting impossibly tight all the while, Colin was not expecting for the cuticle of his toenail to part and a massive claw to pierce the bindings, tearing the rest of the shoe down the seams as he flexed what was becoming a much larger digit. It felt like the mass of the rest of his toes were stuck together, unable to move from side to side like he was used to. They were soon the size of what had become of his big toe, sporting their own singular claw-like nail as well. With the force of their growth, Colin was able to kick the shoes off to some degree, though not without some difficulty, his heels seeming to have expanded and the base of his food a widening circle. But he managed it, soon learning what had become of his feet.

He was not expecting the sight of two massive, stiff digits sitting upon seemingly rounded soles as his heels continued to stretch towards a digitigrade stance. Reflexively, Colin pitched forward, though his top-heavy body was somehow able to manage the posture he found himself in. Heels were soon the length of his calves and growing still, pillars of muscle and mass, quickly covered over in that greyish-black skin. Below the belt, as best he could tell, Colin was all alien, and though the sight of it was rather perplexing, to say the least, Colin couldn’t help but feel ecstatic at the power his legs possessed. If the changes kept going like this…

Colin was soon taken out of his reverie as the contours of his briefs were pulled away, leaving him functionally naked. With that, his now twelve inches were on full display and growing still. Its size seemed fit for a farm animal, though its shape remained overall human as it continued to grow. It took Colin every ounce of willpower not to touch it, though be it the changes themselves or his perception of them, he stayed painfully erect and leaking his arousal. The persistent tingling made it impossible to know when it would stop!

Curious, Colin reached behind him to touch a massive, muscled ass, pert and perfect as his human equivalent had been. His rectum seemed to be in the same place, at least, though it was of little concern with the overall alteration of the outer package. He was massive, powerful, and still growing, almost eight feet tall now and thankful the ceiling in the chamber was so high. Arms bulged outward, and flexing them curiously, Colin noticed his fat fingers were lengthening beyond the contours of his arm, and the same claw-like protrusions burst forth from under human nails. As he watched the final formation of his hands to their alien form, it seemed they were functional in the human world, keeping the same level of articulation he was used to. He would have to trim the nails, of course…

Not expecting it to change further, Colin was shocked to feel the head of his cock start to taper, darkening toward a reddish inhuman shade. It formed a crown of sorts, the foreskin no longer present as it thickened all the way to the base. Testicles seemed swollen and heavy on his frame, though the fluids leaking from his member seemed largely human, as best as he could tell. Perhaps he was a hybrid of human and alien physiology? It was impossible for him to know. Still, even with strange ridges down the base and its pulsating girth, Colin had never been so turned on by the sight of his member alone. He would have to touch himself and cum soon, the urge growing to maddening levels!

The discolored leathery skin spread up his chest and torso, the proportions of his muscles altering just enough to give him an alien look. Far from looking gaunt, however, his torso was compact, powerful, and just as heavy as it had been in its more human state. His internal organs seemed to shift slightly, making him slightly queasy, though just as soon as the changes started, they stopped, Colin no worse for wear from whatever had happened. He could still breathe, his heart was still beating, and the acids in his stomach had not leaked into his organs to damage them in any way. Whatever had altered inside of him didn’t seem to be life-threatening, removing that fear from his mind, at least for now. 

“Colin? Colin, are you OK?” Came the voice of his commander, though Colin was currently exhilarated by the shape of his body to respond. He was sure his erection was a cause for concern, though he didn’t want to draw attention to it until it was time to touch it. And that time was drawing ever near…

By this point, only his head remained devoid of the alien skin, though the persistent tingling seemed to indicate it was soon to alter in its own right. The first such change was his hair loosening from its sockets, falling to the ground around his massive, alien body. Hair short-cropped as it was, Colin figured it wasn’t too big of an issue for his military service. But it was still a little alarming to lose his blond hair, heaving him bald as he reached up with his alien hands to rub the bare skin. Thankfully, his hands were just as sensitive, and he was aware the ashen skin was spreading over his scalp, taking away his humanity with each passing moment. Yet, with how horny Colin felt at the moment, it was simply too hard for him to care. 

“Colin, are you OK? How is-” A voice came on the intercom, though it seemed to be cutting out from something on the other end. Colin didn’t care one way or the other, more focused on the changes and the pleasure they were providing. 

“Yeah, I’m…ooohhh…” Colin moaned as his lips started to stretch, and his ability to talk was temporarily altered. His breath was coming out in wisps like he was losing the air too soon. Almost as though his lips were…

Of all the changes to come over him, Colin was not expecting for his lower lips to split apart, as though they had been ripped from his jaws. That was not to be the case for long, however, the twin flaps of skin expanding in front of his face, tearing painlessly from his cheeks and splitting into twin protrusions in their own right. Billowing in the air of the room, Colin was reminded of the aliens in the ‘Predator’ franchise, though the thin flaps were unique as much as his eyes could discern. They stuck out in front of his face, and Colin could feel the fleshy substances prickling with the formation of edges of teeth, his own pushed outward for the new dentures of this alien being he was becoming. 

Playing with the surprisingly flexible muscles of his newer jaws, Colin eventually closed them, pulling them over his face and feeling more comfortable having them in their resting state. His own teeth along the top of his human jaw were getting sharper as well, more pointed, likely giving him a menacing visage. He was not likely to get a date with a mouth like that, though Colin found it impossible to care with the power in his body. Mouth opening, his jaws stretched to the point where they made his eyes water, the joints to move them just below his eyes. It was bizarre, to say the least, though was it really that bad if the trade-off was gaining such power in his body? Colin was certainly prepared to say so!

The rest of his head was soon to alter as well if the tingling over his skull was any indication. Nostrils persisted, though the bridge of his nose melted into the skin. His skull expanded around his newer jaws to provide them the proper articulation points for muscle to do so. It seemed to pinch slightly, pushing forward in a humanoid visage, though its length dwarfed his former human equivalent. Ears, too, were swallowed, though Colin noticed no lack of hearing from the minute canals that persisted. Bumps formed along the same plane as his ears had once sat, though their purpose was lost to him for the moment. 

Yet, even with the changes coming to their inevitable climax, Colin’s erection persisted, and it was harder for him to focus on anything else. He couldn’t help but love the shape of it, especially as the base of it started to swell, looking like some sort of canine knot almost twice the circumference of his current maleness. His cock bobbed up and down as though preparing to blow his load without even touching himself. With the size of his hands and the girth of his meat, Colin felt he was up to the task, and he would be remiss for leaving his member alone at the moment of his baptism into his new form. 

Groaning, Colin grabbed his alien girth, the pleasure radiating from his rod more than he could have ever expected. Waves of ecstasy started to play over his body as he stroked, prompting him to close his eyes and give into the form. He was exhilarated by the sight of his extraterrestrial form, something beyond his understanding but something Colin could hardly bring himself to lament. He wasn’t hot by his previous standards, but he was every bit the muscled beast he longed to be for all these years. With that, how could he be dissuaded from loving every moment of his new body?

“Colin, are you-What are you doing?!” Came the voice of his commander on the speaker, obviously shocked at the lewd display. Though Colin could hardly bring himself to care, aroused as he was. His member was leaking copious fluids at that point, and Colin was almost tempted to taste it, though had enough restraint to avoid doing so in front of other eyes. Still, the grip of his massive hands was amazing in its own right, and the remaining modesty Colin possessed figured he could pass it off as par for the course of his change. So, ignoring the summons of his superiors, Colin continued to stroke, eager to feel what it was like to ejaculate from a real alien’s penis!

Rubbing down the rest of his body with his other hand, Colin used his love of the alterations to spur on his arousal. His perfectly defined pecs, massive chest, bulky arms, and deft fingers, Colin played over it all with eagerness and precision. Exploratory hands even moved down to cup his balls, teasing his rectum and gripping his firm buttocks with fervor. Though it was his other hand gripping his cock that really did it for him. Running over the contours, playing over the ridges, and above all teasing, the edges of the knot were almost as good as squeezing his balls directly. With that pressure, he was primed to pop at any moment. And why shouldn’t he, with the powerful and horny body he was given?

“Oohhh…oh fuck…gonna…hhggggg!” Colin called out in his deeper tone as his cock spasmed and its shaft blew a pungent stream of cum, coating his hand and the chair in viscous fluids. His orgasm went on far longer than expected, though Colin was hardly in a position to care, aroused as he was. It was pure bliss to be able to ejaculate from such a member, leaving him shuddering as he reveled in the body of his dreams. Disgusted comments rose from the speaker, but Colin ignored them, pumping his alien shaft for every ounce of pleasure it could provide.

With that, the creature that had been Colin in body looked up into the cameras, jaws parting in an alien semblance of a smile. Though his body was no longer human, his mind was just as much as a good soldier would need it to be. Even as the minutes passed and the tingling of change ceased over his body, no alien mind, no instincts pervaded his awareness. He was very much himself, and much more, a powerful, muscled alien being out of his wildest imaginings. He figured it would take some getting used to in the mirror each day but overall had to admit he was impressed with the end result. He was certainly the most physically powerful man in the military, and in the human race, though such a moniker no longer applied to the being he had become. Still, if this was the only downside to the serum, the military would get everything they wanted and more…

“Looks like the serum is ready for further volunteers,” Colin said in a gruff voice that was still unmistakable for English. He meant it, given his love of the results of the project. And, with his lust at a premium, he was certainly eager for more recruits to join his unit…