Author's Notes:

Chapter 3, hooray! I don't really have a lot to say about this other than it's Twilight-centric and the following chapter is Rainbow-centric. That one's about half done as of time of uploading.

Chapter 5 will end the first "arc", and then some new ponies are going to be introduced.

Roused from dreams of delightful dancing ponies, William slowly came to wakefulness. He glanced sideways at his alarm clock and saw it was already 10:32, well past the time Rainbow Dash had been supposed to wake him up! He'd heard just about all her excuses by now, but somehow the way she shamelessly tried them out on him in her delightfully squeaky voice never seemed to get old.

Realizing he had nothing on today but playing with the candy-coloured equines who'd entered his life over a month ago brought William a great sense of personal relief and satisfaction. William could have lazed back in his large, comfortable bed, one of a size that was appropriate for a man expected to fuck many, many ponies, and listened to the birds singing outside all day.

Up until his bladder got the best of him, anyway. Several minutes later William was emerging from the bathroom with a sigh, tugging his long pajama pants back up around his hips.

Now, after a whole month of living with Twilight Sparkle and Rainbow Dash, one would think he had seen all their tricks! He'd felt, tasted, smelt, groped and teased every inch of their inciteful bodies and yet they still had plenty more surprises in store. The trip back to William's bedroom took him past a long series of floor-to-ceiling glass window panes that overlooked the large pool area at the rear of his house, where Twilight Sparkle was currently laying out under an umbrella, reading a book.

He intended to simply pass her on the way to his room, get fully dressed and come right back out to check on her. No point in schmoozing all over one of his favourite ponies in his pajamas, after all! Maybe he'd even dig up some swim trunks and invite Rainbow to come and do laps. Yeah... Innocent, happy stuff. He could probably go a couple of hours without mounting up on those poor ponies. Their plump, well-cushioned buttholes could use a nice, thick... Rest.

It was just too bad for him that even an enlightened human in this day and age still didn't get to decide whether or not he was completely mesmerized by those lithe, limber little bodies! Silly human boys like him needed to realize their cocks and sperm were just prey, hunted to near-extinction by their natural predators: voracious pony buttholes! He'd be happier knowing he'd been born to get stiff when ponies commanded it, and not a moment later.

So while at first he passed by at a brisk pace, it wasn't long before his legs began to feel like they could barely continue on. He wanted to stop and stare, and he soon found himself slowing to a nonchalant stroll, stealing darting glances out of the corner of his eye at purple-fleshed perfection. As he reached last pane, William simply stopped and stared, planting his nose against the glass and not lifting it. A lump formed in his throat as he perved on Twilight Sparkle's body like a neighbourhood stalker. If she caught him, he'd never hear the end of it!

Twilight's deeply oversexed form was sprawled out on a towel skirting the edge of William's pool. The Alicorn looked as composed and dignified as he could ever remember, and yet...

Her top half, mostly obscured from where he was standing, was much the same as he remembered it. She was the same "stepped out of a cartoon" pony as ever, with her messy, piled-up mane of pink and purple, huge floppy equine ears and slightly pointed features. Best of all, however, would always be those extremely large eyes that positively glowed with soulfulness and empathy; the reason he'd fallen so deeply in love with her.

One front hoof was planted on her towel, while the other was delicately turning the pages of the book she was deeply immersed in. Sometimes, when her hooves were preoccupied, the bio-droid’s TK field would activate, her horn lighting up and the pages turning on their own.

As he watched, Twilight raised a hoof to slightly shift a pair of thick-rimmed reading glasses perched on her snout. Her mouth was wide open, cheeks bulging a little from a popsicle wedged tight inside.

Poor William! It should be him in there. As he watched her mouth pursing around the pole, sucking the flavour out until the ice turned white, he became fixated on how wet and ice-cold the inside of her mouth must be right now. He chewed his lip, growing more jealous of the flavoured treat by the second.

His eyes were naturally drawn to Twilight's Cutie Mark, the six-pointed star he'd doodled on his notepads and textbooks all through college. Even now it still held an air of mystery and wonder about it, a representation of the bonds formed between friends. It was the purest part of that lewd pony body.

As he stared at it, something struck William as odd. Had the star grown a little bigger? His breathing began to mist the glass as he tried to get a better look.

It wasn't easily perceptible at first, but Twilight's hindquarters had ever so slightly expanded. When she had first arrived in his home, he'd been delighted with her already fat, round ass, but the tushy providing cushion for the pony now was something else entirely!

Now he was sure something had changed about her. Her booty had grown around the edges, now peeking up a tiny bit above the curve of her spine, slightly higher than her shoulders. Each cheek was rounder and more flush, with more weight and heft and just "there-ness" to it, protruding up at all times like an open invitation. Her legs were longer as well, her hindlegs in particular thicker around the thighs, as if to support that obscene pair of fleshy buttocks.

There was a little thud from below as William realized he'd been joined by a fierce little soldier standing up between his thighs. Yes... A little war-tent was being pitched down there with enough force to slap the large glass door. It wobbled gently for a moment before settling down.

William realized he hadn't breathed in the last few moments and reminded himself to do so. Then Twilight shifted her position on the towel and he promptly forgot again.

Despite its new size, her butt was still firm and lifted enough that at the right angle you could see right between her thighs to the twin temptation-spots winking invitingly. She was more relaxed and easygoing about it here than she would be in a public environment. After all, she was well aware that the exposure was an open invitation for males to mount her and pump her full of virile seed, but also content that the only "stallion" who would do so was one she would welcome the sensation from. This sight was for William's eyes only.

Her pussy looked much the same as normal, perhaps a tad smaller, but her pony butthole was another story altogether. The once cute and small hole seemed to have grown considerably over the last 24 hours or so, the flesh encircling it thickening up considerably. She now sported an inviting donut-shaped pucker, that seemed to move like a pair of lips even in repose. Twilight's newly-developed puffy butthole looked fuller, plusher and like it would be much more soft around a cock.

William finally leaned back from the glass and tried to shrug off the raging hard-on that had formed in his pants long enough to move to the computer terminal beside the glass door. "Umm... Computer?"

The wall-mounted screen lit up, hummed, and then began to protect a holographic shape onto the floor beside him. After a few moments, it solidified into a shimmering 3D replica of the ruler of Equestria, Princess Celestia. Just a little Artificial Intelligence system he'd had installed sometime back.

She trotted up to his side, lowering her head slightly to allow his hand to "push" through her vibrant bubblegum mane. The hologram responded as if they'd touched directly, hair bunching up around his fingers before dispersing down her back again.

"Please, call me Celestia. What is it, William?"

"It's about the, uh..." He swallowed. "It's about one of the bio-droids I purchased."

She chuckled, hooding her eyelids seductively. "My faithful student, Twilight Sparkle. Yes, I know all about how well that's worked out for you. I do hope you're not interfering with her studies."

"More like she's interfering with mine," he huffed, glancing back out at that impossibly-perfect figure outside. "She's changed. A lot."

His face flushed. " What happened?"

Celestia glanced out the window, then turned back to William. "Almost all bio-droids undergo a few cosmetic changes here and there during their first month with their owner. Didn't you know?"

She clopped a hoof on the ground and a display popped up behind her, a seemingly endless array of diagrams and numbers as she continued to lecture. "Simply put, the organizations in charge of creating bio-droids observed a higher satisfaction rate, and lower return rate, if the bio-droids carefully compiled data about interactions and incidents involving their hosts, then used that data to select alterations to their bodies more likely to please their owners."

"Millions of points of data can be observed every day in how the bio-droid is spoken to, their living environment and the liberties provided them, as well as their owner's thoughts, feelings and emotions towards them..."

"But I never asked for..."

"And how they're touched!" she finished with a cheery grin, clopping her hoof again. The flickering hues cast across her flank died as the displays vanished.

"And you have been touching Twilight quite often! In fact, in terms of hours spent in physical body contact with the bio-droid per day, you definitely fail to fall within what I'd call a "normal user's" intake levels." She laughed coldly under her breath, eyes narrowing as he squirmed on the spot.

"You've been quite a naughty boy, haven't you, Mr. Keller? You went ahead and turned Twilight into that sort of girl!"

"I have to turn her back right away, then. There's no way she can be comfortable with a body like that, is there?" His eyes flashed back to Twilight, eyes roving up and down that supremely-sexual body that seemed specially catered for hard fucking. He'd be kinda sad to see it go...

Celestia grinned again, nuzzling his neck. "Are you suuuure? People say that once a bio-droid has custom-adapted its sex organs for a specific owner, there's no going back for either of them. It's like a lock and key system: she won't fit anyone else."

Celestia cackled at his obvious discomfort, not giving him a second to recover. "The experience of a bio-droid's custom-tailored flesh has been described as one of the best physical sensations available to a human being. Why not go try her out first, mm? You proooobably won't get addicted too bad!"

"Princess, please! How do I turn Twilight back?"

She leaned into his side. "Haven't you heard a word I said, William? Twilight has been quietly collecting your data all this time, but this change wasn't forced on her. Hmhm, not by any means, no."

"She's been having late nights every night this week sorting and compiling the data you provided for her to arrive at these very, very carefully chosen changes for you. I don't envy the boy who has to tell her he's going to flush all her hard work down the drain, hohoho~"

William glanced out the window. Princess Celestia explained bit by bit that Twilight had made the change from studious, innocent nerd to slutty pony librarian just on the off-chance she might be able to tease that little bit more spunk out of his nuts. It had his erection so stiff it felt like it could break right through that glass!

Each little whisper from the Sun Goddess's mouth seemed to worm its way into the root of his cock, pumping a little more blood in with each passing second. William’s stiffy was becoming painful, and he finally couldn't take another moment of it.

"Thank you, Celestia. Computer off."

"Have fun!" she giggled, as her hologram faded to nothingness. He opened the door and stepped out onto the patio, crossing the tiled area to where Twilight was laying.

Twilight turned the pages of her book and took a few contemplative suckles at the sugared treat in her mouth. It was one thing to truly devote her mind to studying the history of bio-droids and learn about the origins of her own species, but the advanced mathematics and computational formulas that went into the gene-splicing and creating the artificial womb was making her head spin! There was so much to understand. Her lips sealed tightly around the end of the popsicle as her throat worked hard enough to turn the blue ice fully white!

How had a species that had taken billions of years to evolve to its current state managed to go from conceptualizing her species, to making it a reality, in just a few hundred? It bordered on magic...

Twilight's thought were suddenly interrupted as a large human hand settled on the thick globe of her right buttcheek, the flesh yielding very nicely to the contact. As the familiar shadow of William's body began to cast over her, the purple pony unconsciously spread her thighs apart. "Mmmn..." Scientific thoughts no longer occupied her mind!

William groaned in her ear, a needy, urgent sound, and the pony began to get wet. Her skin grew flush and her pussy slippery as she realized he was about to take care of her needs. The pair's groaning intermingled as he settled down on top of her.

"What're you reading?" he huffed in her ear. His fingers closed around his stiffened cock, bringing it closer to her thick butthole.

Twilight's little tongue hopped out of her mouth to play almost immediately. She raised a hoof to catch her icy-pole as it slipped out of her mouth. "Mmn. Ah."

Aware of his eyes on her, she pushed it back into her mouth, all sultry licks and wet lip-smacks. She heard him groan again, and knowing how captive he was to her charms helped her calm down a little bit! It wasn't good to act like a pig in front of her owner, now was it? "Just... Just some things about bio-droids. It's all very fascinating."

Her eyes darted to his cock. It looked as amazing as ever, the fattest, thickest penis she or Rainbow Dash had ever seen, with a steel-hard shaft. She knew it by touch now, having wrapped almost every hole on her body around him! Most exciting of all, however, was that huge, full nutsack hanging under the shaft, the ability of those swinging seedpods to inflame her lust perhaps the greatest mystery to the brainiac of all. Just one stray thought of the sheer volume of sticky hot semen he was storing in there was often enough to put her in heat! " You're looking extra-large down there today, sir."

He slapped one of the cutie's meaty buttcheeks, making it jiggle. "Ahh.. Yeah, I am," he said, seemingly lost for words, looking down at her ass hungrily.

"Did something catch your eye?" she giggled, knowing full well the effect her new body was having on him. Her heart soared when she saw him completely unable to cope with the new sex-bomb Twilight. By the end of the day, she intended to have his semen flowing like a river!

William got down behind Twilight, bringing his face all the way up to her butthole, inspecting it more closely. Twilight's meaty pussy lips sat snugly between her extra-thick thighs, forming the lower-case "I" that her fleshy butthole dotted. He reminded himself that this volcano-rim she was now sporting was partially his fault as well, his constant need to rail the adorable pony from behind having developed her innocent butthole until it had grown up into the meaty cock-trap he was looking at now. No wonder she'd kept her tail down during all those episodes of the cartoon: she'd have incited the lust of every colt in Ponyville with a perverted rear-entrance like this!

He hooked a fingertip in her donut, gently tugging it open a little further. The muscles inside looked more inviting than ever, the fleshy walls just waiting to contract tightly around whatever he fed inside of her. The outer ring of flesh was the same purple as the rest of her body, but soon gradated to a rosy, flushed pink around the rim. Inside it was an exciting flesh colour that was slightly darker than the rest of her. And then warm, inviting black all the way down. He knew from experience that those svelte inner depths juuust out of sight were better off experienced by touch than any other sense, anyway!

Twilight had been making a show of continuing to turn the pages of her book as he inspected her butthole, but now she had buried her blushing face in her book. Her ass wiggled from side to side as even the slightest amount of stimulation and stretching seemed like enough to bring her to the cusp of orgasm. Not only her physical appearance had changed: Twilight's tingly asshole seemed to be a whole two or three times more sensitive now, putting the otherwise-dignified pony on a hair-trigger.

She turned her head sideways, resting her icy-pole along the length of her book. Bubblegum-flavoured water was dripping onto the pages, but she didn't even notice! Twilight Sparkle was in big-booty Heaven! William could just barely see her love-struck expression over her small shoulder, her right eye as wide as could be, pupil rolling back in her skull. She was stifling her cries, but tiny squeaks and gasps were still making it out of her mouth. What sort of look did she have on her face right now, he wondered?

The rosy smell was inviting, and William leaned a little closer, opening his mouth. He gripped the ring of her donut between his teeth softly, giving it little nibbles. Twilight was trembling as she tried to continue reading her book. "Nnm... Nnm... What are you doing back there? You pervert, come on..." The pages rustled loudly as she gripped it with both hooves.

After giving her rear one more teasing lick, William moved back into a position over Twilight, planting a hand on either side of her small body. He lined his cock up with her butthole and forced the tip inside. She grunted faintly as she bore the brunt of the human's weight on her small back.

William brought his hand down on her plump ass with a loud smack and the pony howled, her lewd holes twitching a little more. His tummy was rising and falling rapidly as he sucked in air desperately. It made him look even more needy and pony-starved than he already was! A few inches from her thighs, that rampant, immense shaft was throbbing painfully, the tip quivering back and forth and releasing semen.

"I can't wait any longer... I'm gonna try out this super-lewd body!"

He nestled the hard tip of his penis against her puffed-up butthole, flattening it against her body, then forcing it apart! A little hiss escaped his throat as he began to nestle his stiffy inside his pony girlfriend's hot hole. "It's even better... I didn't think it could feel better, but it does!"

Inch by inch, her naughty pucker accepted his cock inside. Spanking the pony's fat, jiggly ass made it tremble around his pole, tightening up in a way that made him want to do it again and again. Her body had become so lewd now, he couldn't help himself! His hand cracked her butt again and again! Twilight arched her back and raised her plump ass higher, marshmallow hooves pressed into the towel. "Ohhh... M-More! "

Now that William was inside, his tension was already fading and he was already starting to feel nice and comfy, more relaxed. The way her body was pulsing gently around him, sultry invitations to stick his cock a little deeper, was almost too much! He'd pop a piping-hot load inside her steamy insides in seconds if he wasn't careful! He began rhythmically sliding that hot prick in and out of her stiffy-teasing rear-entrance.

William's breath came out in hot pants as he growled at the pony under him: "This new body is too much... I can't believe you'd change to look like this, haaahn... It's got me so backed up, I need to cum!"

Something about the heated tone of his voice really got to Twilight. It made her feel good. Powerful! Her lips curled into a grin and she moved back at him. To think that she could make a man so pathetically grateful just by letting him nestle between her thighs like this, it absolutely invited more research. Lots more study sessions. The next time she spoke, her usual studious, controlled voice was tinged with a tone of lecherousness. "Couldn't you have just jacked off, then? Did you h-have to force yourself on a cute pony while she was just trying to read her books?"

"N-No... It has to be Twilight's nice, warm butt, I don't want to cum with my hand!" He pressed his body firmly against hers, and she realized he was savouring the sensation of her body. She smiled and leaned back into him, easing all the way into the curve of her mate's body.

As his body began to drip with sweat, William held her tighter, wrapping his arms all the way around. "Fuck fuck fuck... I need to fuck Twilight..."

Twilight turned her head enough to plant a kiss on William's cheek. "Shh, it's okay. I'm here for you. Just let me take care of everything."

Twilight started to pant, her curvy yet athletic body reacting with pleasure and tightness to his.

William loved her little body. He needily inched himself into her hot butthole, that shaft all gobbled up by her lower curves while he pressed his face into her neck and mane. His cock throbbed inside of her, balls slapping her ass with each thrust.

Twilight whined as they fucked in tight, rolling passion; their bodies mostly pressed tight against one-another, only their hips briefly parting only to slap and grind together. Her tummy was bulging slightly from the shape of his cock, precum steadily flowing into her. Their lips met and they whispered their love to each other, huffing each other's names out inbetween sexual moans.

As he got closer to orgasm, William's fingers clawed at her most insistently, leaving red marks in that perfect flesh. "Hnn! Cumminggg!" He was moments away from bathing her insides in his thick, naughty seed. A human and a pony locked together like this, such scandal!

Up until now, Twilight had been biting her lip, but as she felt William's cock thickening up inside of her, she knew she couldn't last another moment. She threw her head back, moaned, then collapsed under him, almost entirely spent. She'd cum before her lover once again, hair-triggering even faster this time, and she had no-one to blame but herself. The sensations of this new body were almost too much for her to bear! She turned her head sideways, looking up at him from the ground, and squirmed a little bit. "Hnn! ♥ Hah... J-Just cum inside me!" she cried.
He was going to do just that. He pressed into her tight pony butthole, balls hunching up against his shaft. He buried his face in Twilight's neck and worked his hips with all his strength.

Soon, she felt it: white hot volleys of delicious semen soaking her insides. He didn't pull out until every last drop was all the way inside of her, using her as a semen tank and bloating her slender body with his naughty load. There was a loud, naughty glugging sound as he angled the tip of his cock against her deep inside and released a huge volume of semen into her.

Twilight Sparkle gurgled happily, suddenly pumped full of seed from her favorite cock in the world. She whined and groaned and shuddered until his cock relaxed again, leaving her belly big and inflated and sloshing! Slosh, slosh!

"Hah... Nnnh... You made me... So big."

---

Sometime later, William and Twilight were curled up on the towel together, cradled in each other's arms and hooves. With her experiment a success, she'd reverted her body to its regular form, the cute and small compact pony he'd always loved. He began to slowly realize it was almost lunchtime and he hadn't seen Rainbow Dash at all today.

"Hey," he mumbled thoughtfully, trailing a finger down Twilight's belly.

"Yes?"

"If you changed your body like that because of the data and stuff you, um, observed from me, does that mean that Rainbow Dash did the same?"

Twilight tapped her chin with a hoof. "Well, she should have! We'll just have to wait and see, won't we?"

The two raised their heads suddenly as they heard the sound of the glass sliding door leading to the house being opened and then roughly closed with a slam. "So this is where you two are! I've been looking all over for you! Hey William, you're gonna be knocked FLAT when you see the changes I made for you!"

William and Twilight sat up, the male slowly dragging his dripping cock from Twilight's insides. He took one look at Rainbow Dash and tilted his head to the side slightly.

"You look... the same?"

Rainbow trotted down onto the tiled area to stand in front of them. Sure enough, the pony didn't seem to have changed her appearance one bit since yesterday, she was still the small-butted, stubby-hoofed speedster he knew and loved.

"Aht, aht, aht, William, come on now. I thought you knew better than to judge a book by its cover! I exhaustively complied all the data about my interdictions and accidents involving my host and made one very, very big migration to my body to please him!"

He glanced towards Twilight, then back to Rainbow Dash. "Which is?"

"You are not gonna believe this," she said, grinning ear to ear. Rainbow planted her front hooves on the grass, leaned forwards, and rolled in place, until she was supporting herself on her hooves and stifles, looking at him from between them. Her hindlegs were in the air, sticking straight up!

"Handstand!" She blew her hair out of her eyes and broke out the classic Rainbow Dash smirk.

William raised his eyebrows, moments before he began clapping exuberantly. "W-Wow! That's awesome, Rainbow!"

"I know, right? How can one pony be so totally aw - W-Wait... Uuahhh!" Rainbow lost her balance suddenly and fell forwards, crashing down onto the grass. She laid on her back, staring at the sky.

Rainbow smacked her lips as Twilight knelt down by her side. She needed to make sure her friend was alright! "Yeeeep, that one's gonna need a bit of work."