ROYAL REWARD: Tachyon's Big Experiment (Inflation, Umamusume) (Patreon)

Manhattan Cafe squinted suspiciously as Tachyon led her into the lab. “Do you really think it will help with my illness?” she asked, struggling to resist the urge to cough.

“Oh! Absolutely!” said Tachyon, grinning like a madwoman. “It’s 100% guaranteed! …But even if it doesn’t, it should at least provide a lot of useful data…” 

Manhattan winced. She should know better than anyone it was a bad idea to get involved in Tachyon’s experiments, but if she could just cure her illness… She swallowed. “What do I have to do?”

Tachyon’s grin somehow managed to grow even wider. “Just stand over here,” she said, guiding her over to a large, open area of the lab which seemed to have been cleared especially for her. “That’s right. Now, put this in your mouth.” She passed Manhattan a pipe capped with a pair of straps – its other end connected to a large pump.

Manhattan scowled, but after a second she accepted it. Slipping the pipe into her mouth, she allowed Tachyon to tie the straps for her and stood, her arms folded, waiting. “Mmmmmphf, mmmmmphf mmmmphf?” Alright, what now?

Tachyon licked her lip. “Now? Now we begin the experiment.” And grabbing the handle of the pump with her sleeve-covered hands, she raised it high, took a deep breath, and with one final grin, slammed it down. 

With a boing, Manhattan’s stomach exploded. Blinking in shock, she looked down and gasped to see her belly rising, stretching her dress tight around it. “Mmmmphf! Mmmmmphf!” 

“Hmm?” said Tachyon, raising the handle again. “The point of this experiment is to see how much air an Umamusume can handle before she pops, of course.” 

“Mmmmmphf! Mmmmphf!” 

“How will that help your illness?” Tachyon tapped her chin, looking thoughtful. “Well, they always say fresh air is good for sickness, don’t they? Admittedly, this is recycled air, but, well, I’m sure it makes no difference.” And before Manhattan could say anything else, she slammed the plunger down again. 

A fat bulge of gas swam through the pipe and down Manhattan’s throat, making her belly bloat even larger. Squealing now, she scrambled at the straps, struggling to undo them, but Tachyon had tied them so tight it was impossible. 

In the meanwhile, the other horsegirl continued to pump, raising the plunger and depressing it as hard as possible and picking up speed with every passing second. Soon, bulge after fat bulge of air shot down the pipe and into Tachyon’s stomach, making her gut bloat like a beachball on the pump. Boing! “Mmmmphf!” 

As her stomach blew into an exercise ball of taut, squeaking flesh, bringing her dress to the edge of tearing in the process, it stretched her arms and legs apart and started to suck them inside it. Manhattan squealed even louder as her hands were ripped from the straps by her own swelling body. Soon, she looked less like a horsegirl and more like a blimp. 

“Wow! You’re growing so big!” cried Tachyon, pumping her harder. “Just a liiittle more!” 

Her buttocks, blown to enormous size and exposed by the stretching of her skirt, slammed into the wall behind her, making her squeak. A moment later, her head hit the ceiling. By now, she’d grown so large she barely fit in the space Tachyon had prepared for her. As her sides pressed harder and harder into the wall, she squeaked. 

“Alright, that should be enough for now,” said Tachyon, releasing the pump. Approaching, she placed a hand on Manhattan's breast and pushed, grinning at the squeakiness of her flesh even as Manhattan squealed in pleasure. “Time to run some tests~.” 

***

A week passed before Manhattan saw her chance to escape. She spent all seven days of it wedged into her portion of the lab, her buttocks and her sides pressed against the walls, while her chest and her head bumped the floor and the ceiling. In that time, Tachyon had run her fingers over just about every inch of her body, poking and prodding and pinching, to see how her flesh was holding up. She’d shrunk a little in that time as the air slowly spilled out of her, but Tachyon had wasted no time in pumping her back up again. Now she was bigger than ever – Tachyon refused to let her deflate. 

But Tachyon wasn’t here now – she’d gone out to fetch coffee. Which meant Manhattan had a chance to get out too. 

Wiggling her feet, she managed to kick herself forward. She couldn’t walk properly, but if she could just reach the far walls, she could probably pull and push herself around the building. All she had to do was find someone else and she’d be free! 

Sucking in a deep breath (but not too deep), she pushed, kicking off the wall and rolling forward. This squished her boobs against the floor, making them squeak and her moan, but she maintained her resolve and pushed on, grabbing the corners of the wall and pulling herself forward with a squeak-squeak-squeak of rubbery flesh against wood. Like this, she managed to cross most of the lab. Soon, the door was only meters away, and–

–and opening, to reveal the face of Agnes Tachyon, a cup of coffee in her hand and her stomach rounder than ever. “Oh, Manhattan,” she said, looking her up and down. “Where are you going?” 

No! No, I was so close! “Out of here!” she cried, gathering her courage. “And you can’t stop me!” 

Tachyon clicked her tongue. “You can’t leave just yet.” Placing her coffee on the desk, she grabbed Manhattan by the leg and dragged her squealing back to her corner of the lab. “There’s one last test I want to run before we’re finished with this experiment.” 

“O-one last test?” said Manhattan, paling as Tachyon picked up the pump. 

“Oh, yes.” Tachyon smiled. “I want to see how much air it takes to make you pop.”