By this iR!!tZfBfNXfYvL guy
Contains water expansion via lady parts, belly rubbing, and (somewhat non-descriptive) deflation
 
>Twilight sighed, sinking her head into the soapy bath bubbles as Pinkie walks out of the bathroom with Gummy in tow.
>She really should've gone home instead of taking a bath at Sugarcube Corner.
>Her hair was still standing on end from the scare that alligator had given her just a few moments ago.
>Thick mud from the (completely coincidental) hay wagon drive-by was still sticking stubbornly to her lavender coat.
>"At least she brought the shampoo..." Twilight grumbles to herself.
>The purple mare leans out of the tub as her horn sparks to life, illuminating the shampoo bottle in a dazzling purple aura.
>Concentrating on the pink bottle across the room, she gradually levitates it closer, unscrewing the cap.
>Twilight can smell the saccharine sweet, candy-scented shampoo.
>Leaning back, she feels her rump press up against something ice-cold and metallic, sending an immediate shiver up her spine.
>The purple pony lets out a small yelp, her body spasms a bit, and water loudly splashes around in the tub.
>She loses her magical grip on the shampoo bottle; most of its contents spill out into the tub, foaming up around her.
>Icy sensations cause Twilight's nethers to tingle for a few seconds.
>"Oh Celestia..." she mutters, biting her lip.
>As the pleasure fades, Twilight thrusts her butt back into the shower head.
>It doesn't send another shiver, it's barely even cold anymore.
 
>She thinks momentarily about the absurdity of ramming her vulva against her friend's shower head.
>"There's no way Pinkie would waltz back in here while I'm bathing, right?"
>"Well, there's a chance..."
>"...Maybe she wouldn't mind it."
>Twilight hatches a quick plan, using her magic to turn the faucet knob as her marehood presses harder against the shower head.
>She gets in position, her horn lights up once again.
>Once the knob is turned, cold water immediately spurts out of the shower head, sending more chills up Twilight's spine.
>Twilight moans as softly as she can manage.
>"What would Celestia think of me right now?"
>She pushes all her thoughts aside as freezing water begins to gush into her warm folds.
>Stifling another moan, her hindlegs begin to quiver.
>The hot water comes on.
>Twilight feels entirely new sensations, the water bubbles up and warms her insides.
>Her womb quickly fills up to capacity, expanding ever so slightly to accomodate the liquid.
>She's forced to press her ass harder against the shower head to prevent pressurized water from escaping.
>The purple unicorn sits there for what seems like a few minutes, in pure bliss.
>Twilight's midsection starts to bulge and distend; the shampoo bubbles stick to her round belly.
>Suddenly, she hears a familiar high-pitched voice "Twilight... whatcha doin'?"
>Twilight feels time slow to a halt.
 
>She flicks her eye open reluctantly, seeing a bright pink figure standing just outside the tub.
>She wants to run, right now, and briefly considers it.
>Twilight realizes she'd spew the Old Faithful out of her vagina if she were to take her butt off the shower head right now.
>"Twilight?" Pinkie asks again, a look of utter confusion plastered on her face.
>"O-oh, me? Just- uh... testing out a spell! Heh... can't be taking these long study breaks, right?" Twilight stammers with an obviously strained grin, unable to look Pinkie square in the face.
>"Well, my tail was wiggly and that can only mean one thing!" Pinkie exclaims, bringing her face up to Twilight's so their snouts were nearly touching.
>"What does it mean?..." Twilight mutters, as her belly grows rounder and more taut.
>"It means your tummy's being filled up with water! Look who's right again!" Pinkie chirps, her bubbly smile returning in a flash.
>Letting out a sigh, Twilight realizes just how hot her cheeks are from blushing intensely.
>"I'm so very sorry Pinkie, I'll leave right now..."
>"What? Are you crazy!?" Pinkie practically shouts.
>"H-huh?"
>"Twilight, I wanna see your fat tummy before you go, so get out of the bathtub!" she commands.
>Twilight is left speechless for a few moments... this hadn't been what she was expecting.
>"My... tummy?"
>She contemplates for a few more seconds, looking up at Pinkie's very sincere smile.
 
>"Ok..." Twilight concedes, turning the faucets off and casting a spell to hold the water firmly inside her womb.
>She grabs onto the ledge of the tub with her forehooves, nearly slipping from the spilled shampoo.
>Pinkie steps back, watching her friend heft her weighty belly up over the rim of the tub.
>Twilight pulls herself over with great effort, breathing heavily as her sopping wet coat drips onto the blue tile floor.
>She plops herself into a seated position, resting her back up against the tub with both hooves on her bulbous, soapy belly. "Is this what you wanted to see...?"
>Pinkie nods rapidly, "Perfect, Twilight!"; she rushes over and places one pink hoof on Twilight's drenched tummy, moving it around in circles.
>She places her other hoof opposite the first one, giving Twilight's belly a squeeze and causing the liquid to slosh around. "It's like a water bed!" She giggles.
>Twilight's hindleg twitches from the belly massage Pinkie was giving her. She begins to pant heavily; her rotund middle rises and falls with each labored breath.
>Pinkie can't tear her eyes away from Twilight's nearly spherical bulge; she pokes and prods it in fascination, causing her friend to squirm in delight.
>"P-Pinkie!" Twilight protests through shaky breath, as Pinkie continues to play with her big bulge.
>Tuning out everything around her, Pinkie plants a soft kiss on Twilight's middle, sending her friend into a fit of ticklish wriggling.
 
>Pinkie continues to dig her hooves in, completely enthralled with her friend's gut.
>"Pinkie! Stop! I'm gonna-"
>It was already too late.
>Twilight's horn fizzles out; she feels a rush of liquid escaping from underneath her.
>A flood of water pools up underneath the two ponies, as Twilight's paunch rapidly deflates.
>Pinkie's bathroom is completely flooded under a layer of water.
>She starts to giggle uncontrollably, flailing her hooves around in delight. "You popped!"
>Twilight stares dumbfounded at her flat abdomen.
>Barely able to breathe, Pinkie writhes around on the floor in laughter until she eventually runs out of energy.
>Both ponies fall silent for a few moments.
>"...Pinkie?"
>"Yeah, Twilight?"
>"Can we... try that again?"
 
<End>