"...I think I'll test it." You told her.
"Are you sure? It could be dangerous." She asked me. She seemed really worried about you. "I don't want to lose my boyfriend in my birthday."
"And I don't want to lose you in your birthday." You replied before you gave her a kiss. "It won't be dangerous, I promise."
"Ok." She nodded. "And how do I use it?" You carefully explain all the functions to her and after 20 minutes she seemed ready. "Ok, I got it. Do you want to become something in particular?"
"It's your birthday. I'll let you decide. My body is your." You smiled at her. She smiled back before she pointed at you with the gun and hit your chest with a small laser beam. "What did you choice? Age? Gender? Racial? Size?"
"Species!" She gladly replied. "I've always wished for a pony for my birthday since I was a kid!!"
"So? I'll become a horse?" You was surprised by her choice. "Isn't your apartment a little too small for a horse?"
"Oh damn, I didn't think about it!! Come on! Let's go outside!!" She seemed more happy than worried.
"I didn't plan to be outside. Everyone could see me transforming!" You shouted as your feel your insides already changing.
"You can't stay here!" She insisted. "The park is near! We can hide behind the bushes!"
You tried to protest but you didn't get a chance to do much more than writhe and twist about in protest, your transformation was progressing fast. You opened your mouth to scream in pain when you felt a pulse against your skin.
The vibration ran up the length of your forearms and chased towards your shoulders with an eruption of sensation that left you gasping. It was unlike anything you had ever felt, it was electric and causing you to jerk in place. It hurt, strumming all the way through your chest as you snapped your eyes open wide and saw your girlfriend pushing you out of her apartment stepping back. You tried to resist but you can't, and she managed to take you to the park.
Meanwhile, your fingers began to thicken and your nails were growing heavier and weighing down as the fingers began to swell wider and your wrist thickened as well. The bones were starting to grow heavier as the muscles began to grow in answer to the size of your forearms. Your bones were aching slightly as you cried out raggedly.
"Shhh! Be quiet! Someone could hear you!" Your girlfriend said as she looked around to make sure that nobody is seeing you. You cried out and shuddered as your shirt began to swell around your neck. "I feel so bad for you baby, it seems that you're suffering!"
It's your first test and you knew that something like this could happen. At least, you're glad that it's you who's suffering and not your girlfriend. Your clothing began to tighten over all your body. You stumbled backwards and hit a tree as your chest swelled open wider and your ear tips started to grow longer, lifting up higher in the air to either side of your head. They were tapering towards the tips, jutting up while your short buzzed hair began to grow longer and flopped in front of your eyes.
You were growing by the moment, stumbling as your pants began to grow too tight and your shirt started to tear and rip along the sides of the chest. You choked out raggedly as your neck began to grow heavier and longer and your arms were growing heavier. The tearing clothes were falling from your changing body, ripping to show your bare chest as there was a splash of copper hide covered you and rushed up towards your neck. Your hair flopped over your eyes entirely while your hands were swallowed with thick hooves. There were snowy white splashes of color that ran up the length of your wrist towards your elbow, something that was followed with the flash of copper red hide that ran upwards.
Your nose was growing outwards, bulging and swelling with your nostrils flaring open wider as your lips grew heavier and softer feeling. You were choking back a noise, the sound erupting free with a wild noises not even remotely human as horse shoes began to form on your hooves. Your body was growing heavier and it was harder to stand on two legs, two legs that were rapidly changing.
Your pants were starting to rip along the line of your ass, bulging and causing you to choke out a whinnying cry as your head grew longer and you felt your jeans starting to give. Your body was throbbing in time with your heart as the coppery red hide was covering you and swelling over your chest. You were being covered in the horse hide, your body growing taller, looming way above your girlfriend, your neck thickening by the moment as your nose began to push out into a true muzzle. The nose began to grow larger and softer, the scent of your equine self on the air became stronger and sharper.
Your fingers were forgotten as the thick hooves scrabbled to try and keep yourself upright, your shoes split open wide as your toes began to grow into a hoof, but the tightness of your pants distracted you. The jeans were painfully drawn around your waist, pinching parts of your body that made you flinch and shudder and you couldn't even get them off, no matter how hard you tried.
"Here, I'll help you, that doesn't look comfy." Your girlfriend spoke up. "It's happening quicker than I thought!"
You erupted out a rush of whickering sound, your ears flapping flat down to your head as your pants were grabbed. You were offset, unable to quite brace yourself as you felt her hands tearing your pants open, splitting them right along the seam. You stumbled to the ground, your knees hitting hard as your girlfriend cut away the tight denim and eased the painful pressure that was growing worse by the moment. It split right along your loins and you groaned out as your legs began to grow, your hips popping strangely.
You splayed your arms out, your hooves scraped to the ground while your cock fell out and swung back and forth. It was humiliatingly exposed, flopping this way and that along your inner thigh, hitting against your skin. You choked out a ragged noise, your breathing became shorter and heavier, your chest tightening as your muscles became heavier and stiffer, swelling open wider as you scraped your hooves against the ground. You tried to hide yourself, but there was nowhere to hide in that park.
Your balls fell out from the jeans, swinging back and forth to bump against the inside of your inner thighs, your powerful thighs and legs were growing. Your chest was swelling open wide and became more barrel like, more like a horse. Your cock was bumping against your knees as it was drooping down lower, falling further towards the ground as your balls warmed and began to bulge. You squealed and gave your head a shake, swinging away to try to hide your humiliation, but you were awkward on all fours and couldn't quite move gracefully. You nearly fell down on your belly, squealing a little bit while hands slipped up right along his belly as your girlfriend was touching you.
She was looking at you closely as your changes continued to rip over you, making you grow heavier and your arms formed thick heavy legs. The muscles rippled beneath your copper red coat and you drooped your long neck down as her hands slipped up to playfully wrap around your cock.
"At least you're way more endowed now." She giggled lustfully. You flinched and tried to jerk away again, stomping a hind hoof, but she followed you. "What did you think I'll be doing with a horse?!"
"EEEEEEEEHEEEEHEEHEEEE!!" You whinnied out in shame as you felt your cock swaying beneath you, causing you to swing your head towards your chest to look at yourself. There was a flash of black and pink under you, making you startle and stomp a hind hoof as there was a feel of pain that burst over your lower haunches. There was a pressure that caused you to jerk forward as a thick tail began to push outwards from the base of your spine and fell down along the length of your hind legs.
You were distracted by the brilliant penny bright tail only briefly, because your true focus was on your changed cock that was swinging back and forth between your legs. The thick heavy flesh was pulsing and swelling open a bit wider, bumping against your undercarriage as you stumbled backwards and felt fingers moving up to slide right against the line of your underside. You was confused and tried to get away, but your girlfriend moved with you and her fingers wrapped right around your tip to heave it upwards, cupping the palm right beneath the glans.
"Oh come on, really?" You thought as you're ashamed of your girlfriend's fetish. "Don't make such a fuss or I won't turn you back, baby." She seductively grinned, purposefully squeezing along the glans with a flex of the finger tips. "It's the best birthday present you can give me."