Thick, virile musk filled Nathan's lungs as the stallion unzipped his jeans. They were a custom job, with two zippers either side of a central flap for the crotch; once opened up, the full bulk of Russ's sheath and sack flopped out into the open. It dwarfed the human's own package, but that was how Nathan liked it. He pressed his face against the smooth, leathery surface of that scrotum, kissed at the bulk of Russ's cannonball nuts. As the black-furred stallion's meat slid out, it sagged under its own weight and slid over the young man's left shoulder. He groaned, lingering for a while to bask in the heat, the scent and the gentle churn of his date's balls.

Nathan managed to pull himself away from the horse's crotch, sitting back on his knees to watch the full bulk of Russ's endowment make itself known. At nearly eight feet tall, the equine had thirty inches on the human, and that size difference was reflected in the enormity of his length. To Nathan, it was downright mesmerising: the length of the human's arm, as big around as his thigh. The top half of it was a fleshy pink, darkening to almost black around the swell of Russ's medial ring. It swayed heavily before him, and he watched its every movement as if in a trance. He could even see it pulsing with each heavy heartbeat, his face drawn towards it inexorably, to kiss, to taste...

"I told you I was big." The stallion's voice woke Nathan from his trance. He nodded vigorously, hands tracing over the contours of Russ's shaft. It was already stiffening from his touch, rising towards the boy's face. A thick bead of precome was already oozing down the broad surface of his equine flare, dripping onto Nathan's T-shirt. The heat was intense.

"I'm, er, not really sure this is going to fit, well, anywhere." Nathan was blushing, unable to take his eyes off that cock. His hands kept stroking, in a worshipful motion. 

"Oh, that's not a problem, cutie," Russ said. "I just wanted to give you a good taste." He reached one big hand down to lift that shaft, nudging the damp flare against the human's face. Nathan let out an involuntary groan of pleasure, pursing his lips to the man's slit and taking a first hungry mouthful of his juices. The salty flavours swirled over his tongue, enhanced by the animal scent; the boy swallowed hungrily.

Eager for more, Nathan began to lick and slurp over the huge width of Russ's cockhead. As the pre kept flowing, it drizzled over his face, smearing over his nose, his mouth, his chin, soaking into the fabric of his shirt. His hands moved more zealously, gripping firmly onto the sweat-damp meat of the horse's shaft, pumping along its length. Peeking up over the crown of that flare, he saw Russ's eyes closed, the stallion breathing heavily, even grunting from the build-up of pleasure. In his Nathan's small hands, that beast of a cock looked even bigger.

"Ngh, damn, kid, you really know how to treat a stallion!" Russ grunted now, and Nathan could feel that shaft pulsing hotter, stiffer, teetering on the brink. "You had a lot of experience with cocks like this?"

Nathan mumbled out a "no" as he worshipped the equine's flare.

"Well, let's see if we can't - nnh - fix that," the stallion panted through clenched teeth, before crying out in a loud whinny. His shaft twitched, and in a split second Nathan's mouth was flooded with a hot, salty gush of Russ's seed. The boy managed to gulp down the first few enormous, heavy ropes, but it was soon far too much for him to handle. He pulled his mouth away, coughing, squeezing his eyes shut as the rest of the horse's orgasm splattered and poured over his face. He tried catching a few more splashes in his mouth, swallowing them with a hungry groan. Every gulp warmed Nathan's throat as it oozed down, and even after Russ's climax had peaked, the human found himself still kissing, licking up the last potent dribbles of spunk.

"That was just delicious." Nathan said, licking his lips. He pulled his T-shirt off, exposing the skinny pale torso underneath as he used the bundle of fabric to clean Russ's come off his face. The human was still achingly hard inside his jeans, the boy having focused all his attention on his partner.

"Oh, just you wait." Russ's smirk caught Nathan off guard. "I promised you a life-changing experience, didn't I cutie?"

The human opened his mouth to reply, only for a semen-flavoured burp to come out instead. He mumbled a self-conscious "'scuse me", clapping a hand over his mouth. Except his hand was bigger than it had been a minute earlier. And much hairier, too. He looked up at Russ in shock, but the horse just grinned down at him. Then, he took a step back, folding his arms across his chest and leaving Nathan in the middle of the room.

The human looked down at himself to realise his torso, once smooth and skinny, was sprouting a thick, soft layer of hair. Not only that, but the boy's chest and shoulders seemed broader, thickening along with the rest of his body. "What...what's going on?" He sounded panicked, though the tone was offset by the sudden realisation that Nathan's voice had pitched significantly lower. His neck felt thicker, longer.  Muscles swelled and bulged against the surface of his skin: Nathan's body swelled from skinny to athletic, and then to downright ripped. Thick biceps bloated in his arms as he sagged back against the foot of Russ's bed, and when he gripped onto the bed frame for support his newfound strength caused him to snap a chunk out of the wood. When he looked down at his legs, enormous thigh and calf muscles swelled and strained against the denim of his jeans. He was aware of his feet bursting out of his shoes and socks, the joints and muscles in his legs rearranging to accommodate his new hooves. As he felt the seams of his trousers start to give, tearing open to reveal thick white hair, his legs seemed to be growing away from him. The entire room felt smaller - Nathan realised he was growing bigger in height as well as bulk.

There was an uncanny shift and tension in Nathan's jaws. His tongue felt fatter, too big for his mouth. Reaching up a (thick, strong) hand, he groaned as he felt his face stretching out into a long muzzle. His nose merged with his upper lip, his teeth thickening; he was dully aware that his ears had migrated north. Nathan couldn't see himself, but as the growth started to ebb, as he clacked his jaws together and his new tongue slid around his lips, he knew what he was becoming. That broad, long muzzle, the pointed ears, the strong jaws, could only be the features of a stallion.

His new taste buds brought with them a renewed surge of flavour from the aftertaste of Russ's equine seed. Nathan nickered in pleasure, glancing over at his new lover - though Russ seemed a lot less imposing than he had before.

"How do I," Nathan paused, the new shapes of his mouth distracting him. "How do I, uh, look?"


Russ was watching with a mixture of lust, pride and wonder. His eyes grew wider as they moved over Nathan's form, from his thick mane to his bulky muscles, and down to... "Fuckin' colossal."

The new horse followed his friend's gaze, and almost cried out in surprise. He had felt a growing tightness in his crotch, but now his jeans were positively bloated with Nathan's package. He reached down to try and unzip himself, but before his fingers came close there was a loud noise of shredding fabric. Combined with the final swelling of his leg muscles, his junk pulsed hard enough to rip through the few remaining seams of his trousers. They practically exploded off him, scraps of blue denim all that remained. Finally free of their confines, Nathan's balls flopped out, inflated almost to the size of pumpkins in a scrotum that was now thick and dark. They sagged pendulously against the bedroom carpet, their sheer size forcing his thighs apart. Sat atop them, where Nathan's penis had been was now a wide, fleshy mound of equine sheath. It was almost as big as his entire head had been as a human. Looking down at it, he was overcome with a sense of power, of virility, of potency.

"I think you're about done, handsome." Russ's voice was dripping with desire. "See if you can stand up okay."

Nathan had a little trouble at first, given the weight of his new body and the awkwardness of hooves. But soon he was stood up in the middle of the room, swaying a little to keep his balance, and found his ears brushing the ceiling. Russ was right: he was a colossus, a stallion three metres tall, towering over the other stallion by a full two feet. He was wide, too, broad shoulders and heavy muscles nearly akin to a bodybuilder. His body was covered in soft fur, a deep chestnut brown that dappled into white at his biceps and thighs. His hooves were tough and black; his lower legs covered with a thick shag of hair the same bright colour as his mane. Nathan tossed his head, letting the long hair fall over his face and posing for Russ.

The now-smaller stallion grinned. His cock had stiffened up again, overwhelmed by the sight of his new stable-mate's enormity. Nathan saw it and felt a deep throb inside his sheath.

"Yeah, I'm pretty sure I can take that now," he said, and parked himself on the end of Russ's bed. The frame creaked under his weight. With surprising grace, Nathan lay back and swung his legs up to expose himself to the man. "How's it looking back there?"

Russ had already positioned himself between the behemoth's legs, and used both hands to heft that enormous sack out of the way. His jaw dropped at the sight of Nathan's rear, his buttocks now two thick, round globes. Between them, where there once was a small, almost dainty-looking human anus, Nathan now sported a thick, dark-fleshed pucker, an equine mound that (like the rest of his herculean body) put Russ's to shame. Wordlessly, he rubbed his fingers over it, feeling the cushy, almost leathery texture and the otherworldly heat. "It's beautiful, Nathan."

At even the slightest touch, that new horse hole send shockwaves of pleasure through Nathan's body. He grunted, shivered as Russ's fingers teased around the fleshy rim; when the other stallion brought the sticky flare of his shaft up against it, he practically whinnied with delight.

"Go ahead, little guy." Nathan grinned, taking pride in the blush that blossomed on Russ's face. 

The smaller equine moved his hands to take hold of those chunky thighs, pressing his cock against that mound. He paused for a moment, and then bucked, sinking the flare and a good few meaty inches into Nathan's newly-inflated hole. The huge stallion neighed out in pleasure, his powerful inner muscles stretching around that flare and the thick flesh behind it. He grunted at Russ to keep going, and it only took a few more thrusts before he had taken him up to the medial ring. Nathan gave a firm flex, and was rewarded with a hot gush of preseed into his bowels.

During this time, the new horse had been watching his own sheath. It was pulsing, twitching with each powerful heartbeat. Nathan felt a build-up of pressure, too, something straining inside its confines. He knew it was his own cock growing inside, but what he didn't expect was the sheer size of the thing. It finally erupted forth from his sheath, and the flare alone was as big across as a dinner plate, juicy pink flesh glistening with musk and preseed. Nathan had no idea how it had even fit inside his sheath, not least because of the titanic pillar of fuckmeat that followed it. By the time he felt Russ's schlong hilt inside his arse, its own bulk causing a thick bulge behind his abdominal muscles, that horsecock was already long enough to reach his ribs. And it kept growing, the pink flesh mottling into dark brown past the medial ring. When it was fully grown, Nathan's muzzle was squashed against his own drooling flare.

Russ paused for a few moments to take in the sight of his lover. The behemoth of a stallion was nuzzling and kissing at his own flared cockhead, thick white hands stroking over the shaft. It was so thick that Nathan couldn't even get both hands around it - he might not even be able to with three. Russ bucked his hips a couple of times, his own weighty sack bouncing off the other man's rear.  The noise of it was delectable, a meaty smack that made the bed frame shake.

Nathan meanwhile had started to suck and kiss at his flared meat, pumping it with both hands the same way he had pleasured Russ's - except this time, he had the means to do it justice. He opened his mouth wider, lips teasing over the broad flare, and let his tongue slather over the surface of his cockhead. It was thick and slimy, long enough to wrap around the colossal girth of Nathan's shaft twice and bask in the intoxicating flavours of his musk. He squeezed firmly, suckling at his flare and guzzling preseed by the pint. Next, he pulled his tongue back, teasing it around the edge of his drooling slit; as he plunged the fat muscle into his urethra, he felt a shudder of pleasure.

That was when Russ picked up his pace, starting to pull his hips back before driving his equine meat deep into Nathan's rear. The plump pucker of the stallion's hole squashed luxuriously against Russ's crotch each time he buried his meat. The extra power to his bucks had a secondary effect, driving Nathan's cock harder against his face until the entirety of the stallion's hypertrophic flare was crammed into his mouth. Nathan groaned and gurgled around his cockhead as it lodged between his lips, the overwhelming surge of lust, musk and pleasure sending him over the edge. As Russ's schlong pounded mercilessly into his guts, Nathan's orgasm hit with the force of a meteor hit. Spunk cascaded through his enormous shaft, hitting the back of his throat and coursing down into his stomach with the force of a tidal wave. Its potent, musky flavours washed over his tongue in a syrupy flood, intoxicating him enough that he only barely registered Russ's own climax pouring into him. 

When Nathan finally collapsed, his stomach had bloated with seed, his own much more than Russ's. He looked down over his new body, fingers tracing over the contour and swell of his bulk. It was everything he had ever dreamed of being, of tasting. He was a stallion, he was huge...and he was ready for round two.