Chapter Text
Umamusume are horse girls, beings born with an innate love for the thunder of feet and the thrill of the race. These extraordinary creatures have walked alongside humanity since the dawn of civilization, their existence woven into the very fabric of history. What sets them apart from humans goes far beyond their equine features - they possess physical abilities that defy normal human limitations, with strength, speed, stamina, and durability that would make any Olympic athlete seem ordinary by comparison.
Along with their distinctive tails and horse-like ears, umamusume carry another unique trait that defines their biology. Cocks. A significant minority of umamusume are born with them, and this is how their species continues. While all umamusume identify as female, their anatomy tells a different story below the waist. Some possess the soft folds of a pussy, while others sport thick, impressive cocks. This dual nature allows them to breed with one another, creating the next generation of racers.
The sheer size of umamusume cocks puts human males to shame. Even the most modestly endowed umamusume measures between seven to eight inches when fully aroused, while many boast lengths that venture into truly impressive territories. These generous dimensions serve a crucial purpose in their breeding practices.
When a particularly skilled or powerful umamusume emerges, she can pass her superior genes to another through passionate breeding sessions. This practice ensures that each new generation of racers becomes stronger, faster, and more competitive than the last. Such breeding encounters aren't considered taboo or unusual in their society - in fact, they're quite common. The most intense breeding sessions often occur between fierce rivals whose competitive tension spills over into raw physical desire, or between lovers whose deep emotional connection enhances the potency of their genetic exchange.
Naomi had seen this dynamic firsthand. As a female trainer at the academy, she worked alongside many others, each dedicated to guiding their own umamusume to victory. The horse girl she trained, the one who held her heart, was Agnes Digital.
“Trainer…! Trainer! Did you see that? Scarlet and Vodka, they were having a pretty passionate argument today!” Agnes Digital practically vibrated with excitement as she trotted up to Naomi, her eyes wide with the latest gossip.
“Oh, really?” Naomi replied, a small, knowing smile playing on her lips.
She and Agnes Digital were partners in every sense of the word. They shared a deep, unspoken fondness for the relationships that blossomed between the horse girls, a mutual appreciation for their beauty and passion. Some might have called them ‘simps’ for the Umamusume, and they wouldn't have been wrong. It was this shared passion that forged an unbreakable bond between them.
This connection made training Agnes Digital a joy rather than a chore. Her natural talent on the track was undeniable, a raw power that Naomi helped shape into precision. Their synergy was a perfect match, leading to incredible results. Just a short while ago, Agnes Digital had crossed the finish line ahead of both Opera O and Doto, a victory that still made Naomi’s chest swell with pride.
“Haah, I could just watch them all day,” Digital sighed, her gaze still fixed on the spot where the two rivals had been. “Watching those two just brings me so much joy, don’t you think?”
“Well, yeah, I like watching Vodka and Scarlet too. It’s always entertaining,” Naomi agreed, crossing her arms. “That aside for a moment, though, shouldn’t we get back to training?”
“O-oh, right! Well, we can train! It’s just… can’t we take a little break first?” Digital stammered, shuffling her feet and avoiding eye contact.
Naomi paused, thinking for a moment. Her eyes drifted downward, and she noticed it immediately: a distinct tent in the fabric of Digital’s flowing skirt, a firm bulge pressing against the material. There was no doubt about what it was. An erection. Naomi nodded with a knowing, understanding smile.
“Yeah, sure thing. Let’s hit the breeding stalls then. That should work out,” she said, her tone laced with cheeky amusement.
“Hawauabbaubbuh!?” Digital sputtered, her face turning a brilliant shade of crimson.
The Breeding Stalls. It was a section of Tracen Academy with a very specific purpose. Think of it like a restroom, but instead of toilets, the stalls were equipped with ‘Breeding Mounts’. These were specialized tools that umamusume used to relieve sexual tension. They were also sometimes used to collect semen from a horse girl’s balls for analysis or breeding programs. For a trainer like Naomi, it was the only real way to help her horse girl when she got like this, since she couldn't assist in that way herself.
And so, they went, Naomi practically dragging a mortified Digital along the corridor. As they approached, the sounds grew louder. Moans, whinnies, and the rhythmic creaking of equipment echoed down the hall. This was normal for Naomi, and she easily ignored the cacophony, leading Digital straight to an empty breeding stall.
“Alright, let’s get you situated,” Naomi said calmly, closing the door behind them. She knelt down, her hands finding the hem of Digital’s skirt and lifting it up. With a quick tug, she pulled down her striped, otaku-style shimapan panties, unleashing what could only be described as a monster cock by human standards. Digital was, to put it mildly, very well-endowed. The thick shaft sprang free, already throbbing with need.
“Are you ever going to find someone to breed with for real?” Naomi asked, looking up at her flustered partner.
“Uwawa- I can’t! I couldn’t disgrace my Oshis with such a thing…” Digital cried out, covering her face with her hands.
“Really? I think King Halo or Mejiro Dober seems right up your alley. I’m even sure Tachyon would help you out if it came down to it…”
“No way! I can’t!” Digital wailed, her voice muffled by her hands.
“We’ll get you there someday. Now come on.”
Naomi gave Digital’s plump butt a reassuring pat, her hand brushing against the base of her rapidly waving tail. She gave her a light, guiding push towards the breeding mount. It was a large, red cylinder-like machine, sturdy and built to last. In the center was a single, inviting hole, designed to accommodate the impressive sizes of umamusume cocks. The material was a soft, synthetic flesh, warm to the touch.
Naomi wrapped her hand around Digital’s thick, throbbing shaft. It felt hot and heavy in her palm, the veins pulsing with desperate need. She carefully guided the engorged head towards the machine’s opening, basically a high-tech, industrial-sized onahole.
“Ggguh…” Digital let out a strangled noise as the tip of her cock pushed past the tight rim of the entrance. The initial resistance gave way to a slick, yielding warmth. Once the pleasure hit her, all hesitation vanished. Her hips, moving on pure instinct, began to rock back and forth, slowly at first, testing the sensation.
Naomi settled into a squat at the other end of the mount, her eyes fixed on the point where her partner’s body joined the machine. She had a perfect view.
Digital’s initial, shallow thrusts quickly grew in confidence. The breeding mount was designed for this, its internal texture ribbed and nubbed to stimulate every inch of a horse girl’s massive length. With each push forward, a wet, sucking sound echoed in the stall. “Ahh… it’s so tight…” Digital whimpered, her hands gripping the sides of the red cylinder for support.
Her pace picked up, the powerful muscles in her thighs and ass flexing with each deep, punishing thrust. The sound of her hips slapping against the machine filled the small space, a rhythmic, fleshy thwack-thwack-thwack. Sweat began to bead on her lower back, tracing paths down her toned skin. Her tail, no longer waving, was now stiff and arched, a clear sign of her mounting arousal.
“Nnngh! Yes! Yes!” she cried out, her voice breaking with pleasure. She was fucking the mount with a feverish intensity now, her body a blur of motion. The thick column of her cock disappeared into the machine over and over again, emerging slick with artificial lubricant. The base of her shaft, where her heavy balls swung with each movement, was a mess of fluids. The stall was filled with the lewd symphony of her moans, the wet squelching of the mount, and the frantic creaking of the machine straining under her powerful assault.
Naomi watched, her own breath catching in her throat. She saw the way Digital’s entire body tensed, the way her toes curled in her shoes, the desperate, needy sounds escaping her lips. Digital was fucking the mount like her life depended on it, chasing that explosive climax only a Umamusume could experience. Her thrusts became erratic, wild, losing all rhythm as she teetered on the edge. With a final, guttural scream, she slammed her hips forward one last time, burying herself to the hilt as her body convulsed in orgasm.
From Naomi’s squatting position, she had a front-row seat to the main event. On the opposite side of the breeding mount, a thick, transparent balloon-like bag was attached to a drainage port. It was designed to collect every last drop.
As Digital’s body went rigid in orgasm, the first thick rope of cum shot through the machine. It was a powerful, milky white jet that flew through the tube and splattered against the inside of the balloon with an audible splat. Before it could even drip down, a second, equally massive rope followed, then a third. The cum erupted from Digital in relentless pulses, a continuous, high-pressure stream that showed no signs of stopping.
The balloon, initially limp and empty, began to swell rapidly. It filled with a torrent of hot, thick semen, the milky liquid churning as more and more was pumped into it. The weight of the massive load started to pull the balloon downward, causing it to sag and stretch. Still, Digital kept cumming, her hips twitching and humping weakly against the mount, as if trying to force out every remaining drop.
The balloon grew heavier and heavier, its bottom distending towards the floor. It was now a grotesquely beautiful sight, a swollen, pear-shaped sac filled to the brim with her essence. With a final, shuddering moan, Digital gave one last weak thrust. A last, thick glob of cum oozed out, joining the massive collection inside. The balloon, now incredibly full and heavy, settled heavily on the tiled floor, a testament to the sheer volume of her release.
Digital collapsed forward, her sweaty forehead resting against the cool surface of the breeding mount. Her entire body trembled with the aftershocks, her breath coming in ragged, exhausted pants. “Haaah… haaah… so much…” she whimpered, completely spent.
“Good girl, good girl,” Naomi cooed softly, patting a sweaty Agnes Digital on the head as she slumped against the mount. Her horse girl’s chest heaved, her body still trembling from the intensity of her release.
Naomi stood up and walked around to the other side of the machine. The cum-filled balloon was heavy in her hands, its warmth radiating through the thin plastic. She carefully detached it from the port, the milky contents sloshing around inside. With practiced movements, she twisted the top and tied it off into a secure knot, wrapping it up to prevent any spills.
By all accounts, Digital was a powerhouse. Her victories on both turf and dirt tracks were proof of her incredible genetics. A lot of trainers, and even other umamusume, would be lining up for a chance to breed with her, to pass on those powerful genes to the next generation. But whenever Naomi brought it up, Digital would get flustered and insist her cum wasn’t worthy of any of her beloved oshis. And so, Naomi was always left with the unfortunate task of disposing of the potent evidence.
She walked back over to Digital, who was slowly pushing herself upright. Naomi knelt down once more, her touch gentle as she took the now-limp cock in her hand. She carefully wiped it clean with a cloth she kept in her pocket for just this occasion before tucking it back into the striped shimapan panties. She pulled them up, followed by Digital’s skirt, smoothing everything down.
“Alright, let’s get back to it,” Naomi said, giving Digital’s thigh a light slap. “Feeling better now?”
Digital nodded, her cheeks still pink but her eyes clear and bright. The post-orgasmic fog had lifted, replaced by a renewed energy. “Yeah! Much better! Let’s go, Trainer!”
Naomi smiled and opened the stall door, leading her refreshed and ready partner out of the breeding stalls. The moans and sounds from other stalls faded behind them as they stepped back into the academy hallway.
Today’s training session was looking up.