"It is Christmas, the most wonderful time of the year!" The speaker in the mall blares. Antony, a young Anthelope, grimaces at the declaration. He never really liked Christmas, especially since he was bullied by other kids for being a "faulty reindeer".

He's currently shopping with his mom and sister, he's adopted to the family which stands out and forms yet another point of bullying on the list. His stepsister Nadaline is a Leopard just like her mother; she has modest B cup breasts and a tight butt. Unfortunately, her personality sucks as she's one of the biggest bullies at school, at least when it comes to bullying him. 

It's not just that they have to see each other but live together, even sleep together! She always kicks at the top bunk bed when he's nearly fallen asleep, and always locks the bathroom when brushing her teeth so he gets late for school. Her friend, Penelopy, a Panther, is rather kind to him; she's always trying to shift Nadaline's attention or interfere on his behalf when she deems it 'enough'.  

He's rather fond of her but there is no shot she's actually interested in him, he isn't tall, doesn't have much in terms of muscle and is a herbifore of all things! Even if he was her same age his sister would still find a way to ruin it all for him by telling lies or using blackmail against him if he dared to flirt, a thing she already claims he's doing as there; "Would be no way for a Cub Herby to date an adolescent Feline."

Antony sighed as he shuffled behind his mom and stepsister, his hooves scuffing against the polished mall floor. The scent of cinnamon and pine needles from the holiday displays mixed with the waft of Nadaline’s expensive perfume, making his nose itch and stirring up a sneeze. She was ahead of him, hips swaying with that infuriating confidence, teasing almost, her tail flicking dismissively every time he accidentally got too close, this time tutting him on the nose.  

*Bump!*

A careless shopper bumped into both Nadaline and Antony from the side, sending her stumbling into Antony. She whirled around, lips curling into a sneer, ready to snap at him when suddenly, her leopard spots shimmered. Antony blinked, but nothing.. it all happened so fast, and he was wondering if he was seeing things.

"Watch your step doofus!" She whispered, pushing him off her. The stranger apologized but she wasn't even paying him attention instead focused on Antony and turned to smile innocently at the stranger "It's okay, I'm fine!"

They moved on without further incident, entering one shop after another, mostly things that interested his mother or sister, especially since he didn't want to be here in the first place tough something caught his attention as they entered a toy shop. There where a bunch of wooden carved figures and symbols and one rather intrigued him, it had an Egyptian aesthetic wich he was rather curious about, a special interest of his. He asked if he could have it but his mother declined, grumpily he walked away but noticed she secretly purchased it a few minutes later.

They left the store to eat a small meal, he had a nice warm hotdog and hot chocolate, his sister nothing as she was on a diet but she did steal a few of his mothers fries from her burger and fries.

Another agonizingly long hour passed in the shopping mall before they entered a clothing store, here he mostly sat on a bench untill his mother called him over to try on some things; his sister was already doing so on her own. Since it was rather busy, he had to share the same stall with her.

The cramped fitting room smelled of synthetic pine and Nadaline’s cloying vanilla body spray. Antony pressed himself against the wall, careful not to brush against her as she shimmied out of her sweater, her tail flicking irritably close to his face.  

“Ugh, Mom got the wrong size again,” she muttered, tossing the rejected top at him. It landed over his antlers, draping him in floral fabric. He peeled it off just in time to see her yank a sequined dress over her head—then freeze.  

A strange, golden shimmer rippled across her fur. Her spots blurred, her tail shortened, and her feline ears… twitched upward, reshaping.

"S-sis, you're—" Antony stammered, his voice cracking as he watched Nadaline’s feline features ripple unnaturally. Her ears twitched again, elongating slightly as the black fur at their tips faded into a softer, tawny hue. Her tail, once sleek and leopard-spotted, flickered like a faulty hologram before shortening into a stubby, deer-like tuft.. no.. anthelope!

Nadaline gasped, her manicured claws no longer.. hooves! They clacked against the fitting room floor as she stumbled back. "What the hell is going on, you brat?" Her voice hitched mid-sentence, the usual sharpness dulled by confusion.

Nadaline’s breath came in short, panicked bursts as she stared down at her own body, now undeniably mirroring Antony’s. Her once-sleek leopard fur had lightened to a sandy tan, her spots dissolving into faint dapples along her spine. Even her breasts felt… smaller, her curves less pronounced. She clutched at her chest letting out a soft squeel, her new hooves clumsy against the fabric of the sequined dress still bunched around her waist.

Antony’s own shock paralyzed him for a second before he instinctively backed up, his antlers scraping against the fitting room wall. "I-I didn’t do anything!" he stammered, voice cracking..

"Liar! .. mom!" she yelled but no response. "What are you standing there for go get mom!" She said pushing him out but their mom was not in sight, to make things worse.. changes started happening inside his pants.

Antony gasped as a tingling heat surged through his lower body, his pants tightening uncomfortably. He fumbled with his belt, hooves trembling, just as Nadaline’s shrill voice cut through the muffled chatter of the store. "Ew, stop! Stop moving like that, you freak!" She recoiled, her own hips jerking awkwardly as her tailbone wich by now was just a stub, twitched beneath the sequined dress.  

A knock rattled the fitting room door. "Everything alright in there?" A bored employee’s voice.  

Nadaline’s breath hitched. "F-Fine!" she squeaked, but her voice wavered, higher-pitched than usual.. similar to that of her little brother!

Antony’s breath caught in his throat as the tingling between his legs intensified, his hips shifting involuntarily. The seam of his jeans strained as something pressed against it—something that hadn’t been there before. His hooves fumbled at his waistband again, but Nadaline’s panicked glare froze him mid-motion.  

"Don’t you dare—" she hissed, but her own protest cut off with a gasp as her sequined dress suddenly sagged around her waist. Her hooves flew to her hips, where the fabric now hung loose.

Nadaline’s breath hitched as the dress slipped further, pooling at her hooves. She scrambled to catch it, but her unfamiliar limbs betrayed her—her movements jerky, uncoordinated. The sequins scraped against the fitting room floor as she stumbled back into the mirror, her reflection wide-eyed and trembling.  

Antony’s pulse roared in his ears as the pressure in his jeans became unbearable. A sharp pop echoed as the top button gave way, and he barely stifled a whimper. His hands still half hooved, half fingers froze over the zipper, torn between horror and desperate curiosity.

Antony’s breath came in shallow gasps as the zipper of his jeans strained further, the fabric pulling taut against the unfamiliar weight between his legs. His hooves now fully formed trembled as he pressed them against the fitting room wall, his antlers scraping the cheap drywall.  

Nadaline let out a choked whimper as her own body shifted again, the last remnants of her leopard spots dissolving into smooth, tawny fur. Her hips narrowed further, the sequined dress slipping past her waist entirely, leaving her exposed. She scrambled to cover herself, but her movements were clumsy.. her new anthelopine limbs refusing to obey.

*Schhrrrrp!* Antonys pants tore as his throbing erection started to strain the seams.. Antony’s breath hitched as the torn fabric of his jeans finally gave way to a big trobing red-hot dog cock! He could feel each individual nerve and vein pulsing with power.

The seam split with another sharp rrrip. His new cock sprang free, thick, flushed, and twitching with every frantic heartbeat. The heat of it pulsed against his belly fur, the tapered tip already glistening with beads of pre.

Nadaline’s gasp turned into a strangled yelp as her own body betrayed her further. Between her thighs, where smooth fur had been moments ago, her cunt bloomed.. a soft, pink, and damp cooch. Her hooves slipped on the sequined dress as she tried to clamp her legs shut, but the unfamiliar sensitivity made her shudder. "N-no, NO!"

Nadaline’s knees buckled as the slick heat between her thighs throbbed in time with her racing pulse. The fitting room air clung thick with the musky scent of their transformations, their fur, sweat, and something sharper like the musk of an alpha.

Her stubby tail flicked uselessly against the mirror as she squeezed her thighs together, but the pressure only made her new slit clench around nothing, making her legs tremble in desperation and concentration.

Antony’s cock twitched violently at the sound, a wet, sticky noise as Nadaline’s body adjusted. Pre-beaded at his tip, dripping onto the shredded denim around his ankles. His breath came in ragged pants, antlers scraping the ceiling as he tried to steady himself.

"W..we'll have to swap clothes, before someone notices!" he said thinking on the spot.

Nadaline’s ears flattened against her skull as she stared at Antony’s exposed cock, her new doe-like instincts screaming at her to flee—or worse, present. Her nostrils flared at the thick musk rolling off him, her own damp slit betraying her with another traitorous pulse.

"Y-you idiot!" she hissed, but her voice cracked into a whine as her hips jerked forward without permission, her hooves skidding on the sequined dress now tangled around her ankles. The cold mirror pressed against her back as Antony fumbled with his torn jeans, his swollen length bobbing obscenely with every frantic movement.

"Just do it, w-we'll figure it out later.. I-I mean, you are starting to look like me..a-and I'm.." Antony meanwhile started taking on more feline traits to that of Nadalines former self.. aside the dog cock but his racing mind started puzzling it together after the bump with that person... it had been a canine.

Nadaline’s hooves scrabbled against the fitting room floor, her body trembling as another wave of heat pulsed through her this time settling low in her belly, making her thighs press together instinctively.  

"F-fine," she spat, but the venom in her voice wavered as her tail stub flicked nervously. She reached for the discarded dress with clumsy hooves and tossed it at him, her movements jerky and uncoordinated while he was figuring out how the hell she was going to pass as him..

"My jeans are torn, just wear these and refuse to take them off no matter what!" Antony said.

Nadaline breathed heavily as she snatched the new jeans from Antony, her hooves fumbling with the denim. The fabric scraped against her sensitive new fur as she yanked them up, the rough seams catching on her damp slit. She bit back a whimper, her stubby tail flicking in agitation.  "They are tight!" she complained.

"You wear skinny jeans all the time shut up!"
Antony’s claws.. claws now, dug into the sequined dress as he struggled to pull it over his broadening feline shoulders. The stretchy fabric clinging to his changing frame, the neckline straining against his thickening throat. His cock, still heavy and leaking, pressed obscenely against the glittering fabric, leaving a dark smear. "Damn it..l-let's hope no one notices!"

The fitting room door rattled as their mother’s muffled voice cut through the musk-thick air. "Nadaline? Antony? Are you decent? I’ve got your sister’s cardigan and-oh, and Antony, I found those gloves you wanted!"  

Nadaline’s new hooves slipped on the polished floor as she jerked upright, the jeans straining against her swollen slit with every panicked breath. She barely recognized her own voice. It was higher, trembling as she squeaked, "J-just a second, Mom!"  

Antony’s feline pupils dilated, his claws snagging the sequined dress as he yanked it down over his throbbing cock. "J-just grab them off her!"

She did only opening the door partially as she accepted the new clothes, they wasted a few more minutes before comming out saying some didn't fit and others they 'liked' pretending that the new 'Antony' liked the jeans so much 'he' didn't want to take them off, with some efford their mother agreed and the cashier coöperated. They could finally head home and figure this out..


The car ride home was suffocating. Nadaline's new jeans chafed against her damp slit with every bump in the road, the denim growing slicker as her traitorous body kept pulsing. She clutched the seatbelt like a lifeline, her blunt hooves leaving crescent indents in the leather. Across from her, Antony's sequined dress strained against his broadening chest, the glittered fabric stretched taut over his twitching feline thighs with a dark weth spot forming on the shimmering material where his cock still hadn't settled, the musky scent of their transformations clinging to the heated air of the car.


The car door slammed shut as Nadaline stumbled out, her hooves slipping on the icy driveway. The denim from her jeans clung heavily to her damp fur with every shift, making her shudder as she bolted for the front door. Antony scrambled after her, sequins catching the porch light as his thickening tail lashed beneath the stretched fabric. Before their mother could even ask for help unloading the car they where already at the door with their excuse being they desperatly had to pee.

Mother gave "her daughter" Anthony the keys while the real one was standing with her legs squezed together at the door, something wasn't right..

Nadaline’s back thumped against the wall as her thighs squeezed involuntarily. The jeans were soaked now, the seam rubbing raw against her swollen slit with every frantic heartbeat but then a new heat started to bloom the moment she made eye contact with her brother.

Nadaline’s breath hitched as a sharp, electric jolt shot through her core—her slit clenched around nothing, the sensation shifting unlike anything she'd felt before. Across from her, Antony gasped, his feline thighs trembling as his cock twitched violently beneath the sequined dress. A slick pop sounded between them, muffled by fabric, as their bodies completed an obscene and sudden exchange.

Nadaline’s blunt hooves scrabbled against the hardwood floor as she doubled over, her jeans now stretched tight around an unfamiliar weight—his weight—thick and heavy between her thighs. Her hands trying to feel and cover up the sudden swollen weight with a schocked expresion in her eyes like she'd just peed her pants, luckily their mother was too busy to notice any of this as Antony rushed to open the door, his glittered pants now digging into his newly grown feminine slit.
They both stumbled towards the bathroom and slammed it shut behind themselves, putting the lock on the latch.

Nadaline’s hooves skidded on the tile as she collapsed against the sink, her breath coming in ragged gasps. The denim of her jeans strained obscenely around the thick, unfamiliar bulge now pressing against the seam—every shift sending a jolt of heat up her spine.

Antony’s sequined dress hitched up as his thighs.. now 'her' thighs as they rubbed together, the fabric damp where his new slit pulsed beneath the glittering fabric. His claws dug into the countertop, tail lashing as he stared at their reflections: her muzzle twisted in shock, his feline ears flattened against his skull. "Wh..what's going on?" (S)he gasped.

Nadaline’s trembling fingers fumbled with the button of her jeans, the denim straining against the swollen heat now pressing insistently against the fabric. A choked whimper escaped her as the seam caught—every tug sending a fresh wave of wetness seeping into the already soaked material.

"L-let me help" antony said, unhooking the button and sliding the zipper down for his sister or.. .. brother?!

Antony’s claws shredded the hem of the sequined dress as (s)he arched against the sink, the unfamiliar slickness between (her) thighs pulsing in time with Nadaline’s ragged breaths. The glittered fabric clung obscenely, outlining every twitch of (her) new slit as (her) tail lashed behind (her).

Nadaline’s breath hitched as the denim peeled away, revealing the flushed, swollen length now jutting from (his) fur..(his) cock! A thick and twitching piece of meat, the tip glistening where pre beaded against fur. Her blunt hooves scrabbled against the tile as she instinctively tried to cover it, but the unfamiliar weight made her movements clumsy, her thighs trembling as she ajusted to her new stance to accomidate the mass between her/his legs.

Antony’s claws dug deeper into the counter as (s)he shuddered, the sequined dress riding up further, exposing the damp, puffy slit now pulsing beneath (her) tail. "Ffh..huuck...is..is this how you fheel all the t-t-time?!" (S)he whimpered.

Nadaline’s breath stuttered as her blunt fingers brushed against the throbbing heat between (his) thighs. (His) cock twitched violently in response, smearing pre across her trembling knuckles. The sensation was overwhelming, with every pulse sending liquid fire racing up her spine, her new muscles clenching instinctively around nothing.

Antony’s sequined dress tore further as (s)he arched, a guttural sound ripping from (her) throat when (her) claws caught the edge of the sink. The scent of their mingled arousal hung thick in the steamy bathroom, (her) slit dripping slickness down (her) trembling thighs.

"Y-oU~.. ah..are... in heat!" Nadaline panted. "C-can..sm-m-mell it!"
Nadaline’s breath hitched as (his) blunt hooves scraped against the tile, the swollen weight between (his) thighs pulsing in time with her frantic heartbeat. She barely registered the arousal spreading down her inner thighs (his) body responding instinctively to the musky scent thickening the air, her balls jumping with excitement and pre release..  

Antony’s sequined dress strained as (s)he arched against the sink, the fabric riding up to expose the glistening slit beneath (her) twitching tail.

Meanwhile at school... (Another storyline)

Her quill snapped under pressure as another wave of unnatural heat rolled through her lean mare body. She was in her early teens, and her curves had just started their development, right now she was the only one sitting in detention, aside from the Janitor, a big old rat. It had all been due to a false accusation, she was a grade A student and friendly to all but she'd been blackmailed and set-up for this.

The janitor’s beady eyes flicked toward her when her hoof scraped nervously against the wooden desk. A drop of sweat rolled down her temple, her mare ears twitching at the sound of his shuffling footsteps. The rat’s tail dragged across the floor as he moved closer, the sharp scent of cleaning chemicals and something muskier thickening the air between them.

Her nostrils flared as another wave of heat pulsed low in her belly, her tail flicking against the chair. The detention slip crumpled under her trembling fingers.. something was off..

The janitor’s whiskers twitched, his gaze lingering too long on the way her uniform stretched across her newly sensitive curves.

"E-excuse me sir.. I-i... Can I use the bathroom I think it's my.." A deep blush flared up underneath her fur.

The janitor’s yellowed teeth glinted as his grin widened, his clawed fingers tightening around the mop handle. "Detention means detention, little filly," he rasped, his whiskers quivering with each ragged breath. Her own breath hitched as another wave of heat rolled through her, her tail flicking up instinctively to expose the damp patch spreading through her skirt. The rat’s nostrils flared, his beady pupils dilating as the musky scent of her unwanted arousal thickened the air.  

Her hooves scraped against the linoleum flooring as she shoved her chair back, but the sudden movement sent a jolt through her swollen pussylips, making her knees buckle. "Please sir.. I.. I really need to check if.."

The janitor’s ragged breath hitched as her trembling thighs squeezed together, the wet fabric of her skirt clinging to her flushed marehood. A bead of sweat rolled down her muzzle when his calloused paw suddenly gripped the back of her chair, his other hand sliding the mop handle between her quivering legs with a creak of worn wood.  

"Check what, sweet thing?" he rasped, his whiskers brushing her twitching ear as his tail coiled possessively around the chair leg. The musky stench of his breath and rut thickened when his hips pressed against the chairback, trapping her between the splintered desk and his heaving belly. She didn't dare to look back at him.

"I-it's private..g-girl stuff, please excuse me sir!" She begged, a quiver in her voice.

"Alright las.. since you asked so nicely, but be sure to get back within 3 minutes or you'll get to spend another extra hour in here got it?"

She didn't hesitate to get up rushing out of the room towards the toilets across the hall. {That damn pervert!} She tought to herself. 

The flickering lights buzzed overhead as she staggered toward the mirrors, her breath coming in ragged gasps. The reflection staring back at her made her ears flatten. Her pupils were blown wide, her nostrils flared, and her usually sleek chestnut fur was damp with sweat along her collarbone.  

A fresh wave of heat coiled low in her belly as she fumbled with the stall latch, her hooves slipping on the porcelain when she finally collapsed onto the toilet seat.

Her trembling fingers fumbled beneath her skirt, feeling an unfamiliar weight between her thighs causing her breath catch. The moment her hoof brushed against something thick and twitching, her ears pinned back in shock. There—where her marehood should have been—swung a plump ratcock, its pinkish length already half-hard against her thigh, twin balls snug beneath.  

A whimper escaped her as she experimentally squeezed, the foreign sensation sending sparks up her spine. The shaft pulsed in her grip, leaking a bead of precum that smeared across her fur. Her reflection in the stall door’s metal showed her muzzle slack with disbelief, her tail curling instinctively around this new, wrong anatomy. Wait.. she had a rat-tail!

She stared down at the foreign appendage twitching against her thigh. It was a warm, pink, hairless length stark against her chestnut fur. A drop of precum pearled at the tip, glistening under the harsh white lights. Her breath hitched as she experimentally ran a finger along the shaft, the unfamiliar ridges sending a jolt through her core. The scent of musk and salt filled the stall. Her tail which no longer resembled that of a mare brushed against the toilet paper dispenser.

The janitor's claws scraped against the mop handle as he felt another surge of bliss wreck his body. His ragged coveralls strained against sudden, unfamiliar curves, heat blooming in his chest, tingles in his ass. His once flat chest now pressing heavily against the coarse fabric with each panting breath. A twitch ran through his new, swishing mare-tail when the scent of the filly's distress still lingered in the air, mingling with his own rising musk.  

His beady eyes widened in shock when he felt electrical shocks running through his cock. Just as his body betrayed him with another surge of bliss his ratty maleness started receding, replaced by a slick, throbbing heat between his hindquarters and a now trobing clit in its place. The mop clattered to the floor as his claws started to soften. He started fumbling with his waistband to see for himself only to squeek like a newborn rat at the lack of his once proud dangling testicles feeling them retract into his body.

The mare's breath came in ragged gasps as her trembling fingers traced the unfamiliar swell beneath her new testies. A sharp, electric jolt shot through her when she pressed too hard, her once-smooth marehood now cradling the heavy weight of shifting flesh. The twin orbs beneath her sheath pulsed unnaturally, their surface rippling like water disturbed by a stone.  She was now an hybrid of her former self and that of the janitor.

The janitors pupils shrank to pinpricks as the transformation deepened with each testicle twisting inward, reshaping with an audible slick that echoed in the empty classroom. A whimper escaped (her) as her insides rearranged, the heat between her thighs flaring white-hot.

The janitor's claws scrabbled desperately at his coveralls as his shrinking testicles gave one last violent throb before sliding upward with a wet, organic sound. His knees buckled as the twin orbs reshaped themselves deep inside his reformed pelvis, the searing heat of transformation making his vision swim. A high-pitched squeal tore from his throat when something fluttered inside him - the first twitch of fresh ovaries settling into place, already pulsing with unfamiliar hormones that made his new mare-body shudder as they anounced his readyness to mate to the world when he felt not one but two sharp pinpricks as each released an ovum.

Meanwhile in some other remote location a trio of new individuals find themselves in an atribute swap of their own.

A group of cubs playing together with army men, two boys and a girl with the girl being a bit of a tomboy.They where playing together untill things changed the moment their hands touched.

The trio's laughter died in their throats as their paws met in a circle. A sharp jolt ran through them like Christmas lights plugged into raw voltage.  

Milo the fox yanked his hand back first or at least tried to. His fingers stuck fast to the otter’s slick palm, webbing stretching between them in glistening strands. His muzzle shortened with a wet crunch, whiskers retracting as his russet fur darkened to a sleek, damp brown. A shudder wracking his spine as his tail thickened, his jeans straining against sudden onset of underdeveloped hips.

The webbing between his fingers stretched tighter, skin darkening to match the otter's as his claws retracted into rounded, water-slick nails. His jeans split at the seams with a loud rip as his the denim catches on his thickening otter-tail now pressing insistently against the fabric. A hot, tingling pressure built where his sheath had been moments before—now sealing shut with a wet snick, the flesh beneath already pulsing with the first throbs of a reshaped clit and cunny.

The otter's squeak of surprise pitched higher as her body changed. Her sleek fur prickling with sudden tufts, her lithe frame shrinking inward. Her tail, once thick and rudder-like, now bristled with squirrel-like fluff, the fur standing on end as her bones popped and realigned. Her fingers, still fused with Milo's webbing, grew slender and claw-tipped, the membranes between them dissolving into nothing as her palms roughened with pads perfect for gripping bark.  

A gasp tore from her throat as her hips narrowed sharply, her shorts sagging where her tiny curves had melted away. 

As for the Squirel? Well he too was changing but in his case it was a mix of them both starting with his genitals.

The squirrel’s breath hitched as his cock clung to his perineum and released with a schloppy, tearing sound. No longer the familiar length of his maleness, but into something new. His thighs trembled as twin sensations warred beneath his fur: the hot, insistent throb of a thickening otterhood outward, while higher up, a fluttering, liquid heat bloomed where his squirrel-maleness had once nestled. His claws dug into the floor as his body betrayed him, the tip of his new otter-cock already glistening with pre, even as the slickness between his hindquarters dripped onto his tail fur.  

Milo’s transformation wasn’t finished either. Milo’s breath came in ragged gasps as his new otter-body shuddered, the last remnants of his foxhood sealing away with a final, sickening pop. His jeans, now torn and useless, slid down his thickening thighs, the denim catching on his rudder-like tail before pooling at his ankles. A sharp, electric jolt shot up his spine as his reshaped clit throbbed in time with the otter’s frantic heartbeat still pulsing through their half-fused fingers.  

None of them knew what was going on or why, not the cubs, the janitor and student nor the brother and sister but it had all started the moment they'd made contact with one another all during this christmass. The effects only lasted during the holiday causing some wicked events during that time and the morning they woke up normally in their own body again. It had certainly been a Christmas miracle.

While the physical changes had passed the mental ones lasted leaving each of them wonder if they'd ever be able to experience it again and making them all the more eager for next years holiday.

The end.
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Notes to self


Hyper is okay up to a point.   I don't much care for body parts that are larger than the people they're attached to.   No specific characters in mind, but I do prefer genital swaps between female cubs and adult anthros or something where there's some kind of power dynamic to upset.  Little sister and big brother, student and teacher, or secretary and boss...stuff like that.  Or predator/prey species like a little mouse or bunny girl and a tiger man.

Definitely not into scat or gore.  Vore shouldn't come up in this.  

Absolute No's that are on your liked list:
Buttstuff or anal play of any sort
BDSM or Dungeons
Enemas
Feral transformations
Fellatio

I'd like the focus to be on the swaps, theft, and the changes in character's bodies and how it affects their behavior, psychology and relationships instead of sexual intercourse.

I think I'd rather see a modern setting.  With a Christmas theme I would suggest some Christmas wishes/magic going awry or twisted instead of a laboratory setting.  