Author's Note: All characters are aged 18 and above.
She just kept growing. Just the horse-half was taller than an elephant now, even just her cocks alone were larger than one. Which was responsible for Keira's pussy twitching uncontrollably, even as she stomped through the halls, trying not to gawk at Mia like all the others. The centaur was leaving, her work done as the gym now had a massive hole and was flooded in cum. It didn't leak thanks to the fleshy boulders plugging the exits.
"Hey, Keira," Annie said, popping up in her path, "We're all heading back home to throw Mia a house-warming party, wanna come?"
"A... house-warming party?"
"Didn't you hear? She outgrew her old place, had to move into a warehouse."
"She's really getting big, huh?" Keira muttered. How could she close the gap now? One of Mia's steps covered entire metres at a time. A race was hopeless, as was any contest of strength, judging by the subtly omnipotent muscles throughout the centaur's body. Morals and grades seemed the only path left, however Keira had no interest in those. She coasted by on a track scholarship and barely paid attention in classes. Not that many others did either as the stench of Mia's orgasm pumped up everyone's nipples and darkened their panties.
"You've no idea," Annie said, not even covering up the tents on her tits, "It's even better than that time she fucked us at the same time. Come on, let's do that again!"
"I've got... other plans."
"Aww," Annie pouted, "Better than getting railed by three horse dicks the size of trucks?"
"Yes," Keira snapped and broke away. She couldn't be that weak, not like all the other sluts around, even if her own body was no better. 'Other plans' were no more than going home and masturbating until she passed out. If she worked out, her thighs squeezed her pussy, and any shirt or bra rubbed her nipples until she couldn't focus anymore.
"I guess Mia's doctor should probably know too," Annie said, giving the athlete pause.
"Doctor?" Keira asked.
"Yeah, she's been studying Mia forever now. She's trying to figure out how to stop her growing. Not that I mind either way. Long as her cocks can swallow me whole, I'm good."
"Where is she?"
Keira's logic was flawed, though it wasn't only her fault. Simple things like walking seemed difficult with her mind clouded in lust, but she maintained her target. There was just one thing she wanted. Annie's info was correct and she found Doctor Roshni leaving a clinic. She was a petite thing, smaller than Annie, which would make this simple. Using her long legs, propelled by baseless desires, she cut the small woman off.
"Can you make me grow like Mia?"
Keira was persistent. The woman kept refusing, however the request was repeated with increasing fervour, each word encroached on madness, yet Keira was deaf to it. All she wanted was a chance to compete with Mia again, and prove her superiority, but small steps first. Eventually, the woman sighed and glanced around, then said the words Keira wanted.
"I think I can help."
She went on to prattle about side effects, dangers of death, though none of it registered. Keira absorbed nothing, only held her arm out, flexed so the veins pulsed across its surface, and waited. A needle pushed in, followed by the cold pressure of something foreign entering her system, then she was gone. Watch out Mia, she thought, a new giant was coming.
Mia, meanwhile, struggled not to crush anything underfoot as she trudged along the street toward her new home. People made it easier as they stopped to gawk, then make out with each other. A few stole touches on her sheaths, stirring the beasts inside, while her balls hovered just a few feet off the ground. They bunched up against her hind legs to keep from spreading them uncomfortably wide, which pushed them higher and rubbed into her puckered ring. Each step was a reminder of Rhona's siblings and the anal mischief they'd done.
Thanks to her being held back and walking slow, the sun was setting when she arrived at the warehouse. Her house. Its shuttered gradually lifted with a powerful whir, whole minutes passed before it cleared her head, taking longer than that morning, and she stepped in.
"Welcome home!"
Mia startled at the combined exclamation, then relaxed as she took in the confetti falling around her. Ribbons streaked across the ceiling and a banner read 'Home Sweet Home' and, of course, her friends were gathered around with party poppers in hand. They didn't care that she was losing herself to her own body, or that she'd broken the gym, and possibly Ms. Grace and the Dean too. Well, they did care, but not for the same reasons as her.
"Thanks guys," Mia said and moved in deeper.
"We got a surprise for you," Rhona said and everyone gestured to a massive cart, on which several multi-layered cakes stood, "I know you eat a lot, so figured we'd buy out a bakery."
"Don't worry," Mia chuckled, "I'll leave you guys one."
Annie huffed as she walked up, "Sorry, had to run back here to beat you. How was detention?"
Mia's cocks twitched in their homes, "Um, it was fine. She just didn't want me 'corrupting the youth', you know?"
"Seems kinda pointless," Mikaela said, joining her sister, "Not like you can go all the way with people. You're way too big."
"Sis, she's fucked pretty much everyone. I'm talking balls-deep penetration."