A human, bit of a pudge, waking up strapped to a rack in a smallish and otherwise empty room, maybe a story and a half tall, but the cieling is dark and shadowy, there's one door, but some cameras facing the table from different directions

Try to struggle, but the restraints allow only a limited amount of motion. Looking around, you see a door, sized for large cargo, with a soft red light above it. There'd be a click, then a soft whrring hum as the cameras seem to activate, then orient themselves on the human, although one camera is pointed at the door, now a pulsing red before suddeny switching to green, the mechanism of the doors grinding and the two halves of the door sliding out and open. 

The light brightens, then  reveals an overly muscled and oversexed red husky carrying a very large drum cannister, effortlessly holding what would have to be a heavy weight when it's just empty, before placing it gently next to the rack - but even then, a loud thud ressonates in the mostly quiet room, revealing the mass of the mysterious cannister. 

After the clanging noise does down, there is only the the faint soft hum of some electronics and the lights, and the breathy panting of the husky, his simple-minded gaze on the human, staring in intense and desperate focused lust.

"Master said I was a Good Boy, and that if I do a," he pauses, his crystal blue eyes staring off to the side a moment as he sounds out the difficult words, "si and tiffic ex spear mint, I can cum." The humans gaze drifts downwards - the husky's cock was a red and veiny 12 inches long and nearly six around, the bulbous knot already fully inflated, with a faintly glowing ring underneath the knot, then his sack, slowly swinging as two basketball sized nuts fought for space with each other and the husky's massive thighs, nesseccating the canine to take a very wide stance.

The husky tilts his head to the side a moment, as if listening to something the human can't hear, before his tail starts to wag rapidly, "Master says it's time to start!" he shouds excitedly, before literally ripping the top of the cannister off with a loud pop and shreak of metal, a bit of milky viscous goo sloshing out and splattering on the ground. The big canine scoops up a big doublepawful of the slimey goop from the canister, then quickly splatters it all over the human's chest, eliciting a gasp from the naked man.

The liquid felt slightly cool at first, but then rapidly warmed up and then seemingly evaporated. A slight tingling sensation grew on the skin where the goop had spread. The human barely had time to process before the husky splattered more goop, this time on his stomach, the warmth and tingling spreading down there as well. The husky repeated the process, now using his paws to spread goop up and down the human's arms and legs, then reaching behind to rub it into the bare skin of the back and sides. He paused for a moment, letting out a soft moan as he rubbed it into the man's buttocks, but eventually moved onward to rub it deeply into the human's feet and toes, leaving only the human's head and crotch untouched by the fluid.

The tingling sensation grew to feeling almost electric, but in a pleasant way, the warmth being relaxing but also somehow tensing. The husky once again took a double handful of the goop - now reaching further and further into the cannister, and instead of splattering it, started gently applying it to the humans shoulders and neck, sliding upwards around the back of the skull. The tingling sensation quickly spread there as well, then following the husky's paws as he trailed over the humans jaw, forehead. 

The canine wiped it over the human's lips, then growled as the man made to bite down on the husky's big blunt finger as it intruded into his mouth, "You be good boy for me or else". The growl sent a shock through the pleasured warmth the human was feeling and he let the husky rub the fluid inside his mouth, having a surprisingly tart flavor before also evaporating and leaving the warm and tingly sensation.

Taking another handful, the husky just placed a big splatter on the human's nose, then forced the human to breath it in. Coughing and sputtering, the human gasped as the tingling sensation invaded his sinuses, the overpowering scent temporarily stunning his mind, then recovered as the scent slowly faded, the liquid again disappeared, leaving only the warmth and tingling. The human's eyes stung sharply as the husky applied it to his eyes, but the human was still dazed from the smell and inhaling the liquid to notice.

Head still spinning, the human didn't noticed the husky taking the largest amount of goop yet, but he certainly felt the impact of the cool gel on his crotch, the husky's broad paws rubbing it in, one meaty paw on the man's balls, the other on the man's cock, both dwarfing the human's average sized equipment. The liquid evaporated again, leaving the warm tingling sensation that was building up like a static charge inside the bound human's body.

While the human was dealing with the building sensations inside him, the husky waited patiently. Three hoses dropped from the shadows in the cieling, and the soft whrring sound of a pump activated from above. The husky took the thicker of the three tubes and dipped the open end into the cannister, then took both of the other smaller tubes in paw. With ease, the husky flipped - rotated, really - the rack, temporarily leaving the dazzed human upsidedown. A small spurt of fluid hits the human's rump, the only warning before the rubbery nozzle of the hose was slid in, the shock of entry eliciting a cry of violation, followed swiftly by a confused moan of pleasure as the tip pressed against his prostate, a small pressure growing as the nozzle both spewed liquid into the human's rump, and inflated slightly to act as a plug.

The husky rotated the rack again, bringing the human right side up. The humans chest heaved, breathing and panting heavily, his eyelids fluttering as the growing sensations in his body began to overwhelm his concious mind. Taking advantage of this, the red husky rudely shoved the third nozzle into the man's mouth. The intrusion gave the man a temporary moment of lucidity, but the nozzle was already pointing down his throat, the back end inflatining to keep him from being able to spit it out. The man's gag reflex started to kick in, only to seemingly disolve as the hose in his mouth joined the one in his rump, spurting the goo down his throat, the warm tingling sensation overriding the automatic instinct.

With this done, the Husky pulled back, and waited. The human's thoughts were muddled as he observed the husky, distracted by the phallic objects in his mouth and rump, the warmth from his skin meeting the growing warmth from inside his body, the static, electrical feeling growing and building. The scent of the liquid was still all over him, and seemed to grow stronger with every passing breath. He noticed that he was starting to moan with pleasure with every exhale, and confused, looked over at the husky, then looked at what the red canine was intently staring at: his own cock.

Without realizing it, the human's cock had grown to full mast, engorged and pulling with blood, twitching a bit here and there. The human moaned again, this time with his hips bucking as the growing warmth and electrical sensation in his cock turned to pleasure, building up. Stars invaded the human's sight as the pleasure built higher and higher, reaching points he never thought possible, and still not coming.

Panting quickly and heavily, writhing in his restraints, the powerful pleasure from his cock overrode all higher thought. Pressure and tightness filled the human's body, deep grunts and loud moans of pleasure reverbing in the room. The husky never had his gaze leave the pleasure-wracked human, but his big meaty paws began to rub up and down his turgid member, exciting himself for what was to come.

Then the dam broke, and the human nearly screamed in pleasure as his cock spasmed once, then a second time, his balls pulling up, his rump clenching the plug in his ass tightly as he came, a large jet of milky white seed spurting from his tip, then a second, then a third, then even more as a seemingly endless mass of semen ejaculated from the human's cock, dribbling all over his face, chest, and the rest of his body, the fluid spraying all around the rack as well, a particularly strong shot hitting the muscular husky in the arm, who then strained with his limited flexibility to lick it off.

With each shot of jizz, the human's body subtly altered. The pudge on his belly and frame slowly dwindled away. The flab on his arms shrank down, the biceps and triceps showing their definition as the human's orgasm-fueled writhing pulled against the restrains. His slight moobs faded away as his chest flattened, the slight love handles receeded into his sides. The most noticable change was in his belly, which slowly shrank down like a deflating balloon, soon leaving his stomach smooth and flat. The changes in all were minor, but left the former medium-shirt wearing human now more fitted for a small.

But the man kept cumming, and the process continued as his body began to bulk up with muscle, his now flat stomach firming and hardening to be a visible six pack, his once flabby and now flat chest rising as his pectorals bulked up, giving him a noticable rise above his ribcage, which expanded slightly outward, barreling his chest and making the man's moans deeper in pitch. The man's straining arms and legs, already bulging from pulling at the restraints, swelled further, twitching as they grew larger. The muscle building in the human's arms and chest met at his shoulders, the growing fibers forcing his shoulders slightly wider, then rolled down his back as it bubbled with new definition.

As the human continued to come, semen dribbling slower from his cock, the changes continued as his hands and feet twitched and spasmed, then swelled slightly larger to match his new frame, fingers and toes becoming thicker. The rack itself creaked, as the man's legs, arms, and torso grew slightly longer, stretching a bit here and here, adding another six inches of height to the man's body.

As the last jet of seed dribbled from the human's cock, his body became slightly thicker overall, more heavyset, and more of the type to need large shirts to accomodate the width of his shoulders and bulk of his muscluature. Eventually the orgasm rolling through his body died down, leaving a more subdued version of the warmth and electrical feeling in the human's body, limply hanging in the restraints from the force of the orgasm before slowly coming to, a small, low gasp escaping as he looked down on his changed body.

The husky walked forward and removed the nozzle from the man's mouth, who hoarsely asked, exhaustion tinging his voice, "What... what did you do to me..." The husky let out a soft bark of approval as his paws and nose explored the human's changed form, then answered, "Making you better and a good boy for master."