Lead in pics:

“S-starlight… a-are you crazy!?” The adult Sunburst stumbled backwards, trying to look away from the tiny filly, currently presenting herself to him, her magic aglow and pulling her tight filly-pussy open.

“PLEASE HELP” Starlight panted, letting drool slide off of her tongue, “...it tingles so much.” The filly’s fat clitoris winked out, the love-bulb bumping into the nose of the teddy bear she was splayed across.

“Starlight, d-do you even know what you’re asking? H-how you look right now?” Sunburst adjusted his glasses, looking back at Starlight and trying desperately to keep his eyes on her face, even as the slick, tight filly-hood demanded his attention. “M-maybe your reverse-aging spell h-had a s-side effect…”

“No.” Starlight sighed, glaring at Sunburst as she flicked her tail left and right. “I’m still the adult Starlight in here.” She tapped her head, before reaching back to pet her tight little flank. “But I’m your hot, tight, horny little filly, on the outside.”

Sunburst stuttered, wiping sweat from his brow. “I d-don’t understan…”

“Yes you do, Sunburst.” Starlight giggled, pointing under the wizard’s cape at his stallionhood, which was quickly sliding out of his sheath as it became erect. “...or at least, a part of you understands. I’ve been trying to catch your attention ever since you arrived this trip, and all you’ve done is nap and snooze on Twilight’s couch… so I figured maybe I’d take the form I had the last time that we fooled around.”

Sunburst swallowed, his eyes now affixed to the winking filly-pussy and tight dark ponut, as his cock filled with blood and slapped against his belly.

“I do have to say I’m a bit surprised, but I could see it in your eyes the moment you woke up, even though you tried to run away… you like me, don’t you Sunburst?” Starlight wiggled her little butt, as she grinned back at the nervous unicorn.

“O-of course Starlight… I-I just didn’t know… if y-you st-still liked me that way… the way when we played ‘doctor’ as young kids… I mean it was so long ago, I thought you were just as embarrassed as I was to bring it up… but when I saw you like that...” Sunburst gulped, trying to cover his fat stallionhood’s cockhead as it began to drip with pre-cum, “...everything kind of came back to me.”

Starlight giggled, moving her rear so it was sticking even more up into the air. “You dummy, I wanted you to take the hint way before this…” She giggled, “Now I’m stuck as a filly for at least another couple of hours… and you’re not leaving me like this!”

Sunburst shook his head vigorously. “N-no way Starlight, I-I’m not a filly-phile! I… I’m just r-remembering those old times, is all… it’s not…” Sunburst gulped as a dribble of fillyjuice slid out of Starlight’s tight filly-cunt - he could practically see steam rising from her hot nethers, “...not how you look right now…”

Starlight grinned skeptically, “Uh-huh… sure…” She looked at his dripping cockhead, bobbing away from his attempts to hide it with his hooves. “You know Sunburst, I’m still a fully mature mare - this is just a spell, right? Nothing illegal or improper here.”

Sunburst swallowed nervously, loosening his cloak. “St-still… I c-could… m-maybe you should m-make me a colt too?”

Starlight frowned, flicking her tail with frustration from left to right again as she stared at the stallion’s dripping cock. “Hmmm… no I don’t think so. I remember how big you were as a colt… and you’re really grown-up.” She giggled. “Filly-Starlight likes what she sees… and she always gets what she wants… now no more delaying!”

Starlight ignited her powerful magic, pulling the cape off of the reticent Sunburst and pushing him forward by his flank until he was standing over her, she noticed that his resistance to her force lessened as he got closer. She could feel his hot cock resting on top of her soft, filly-furred rump, the heat and wetness of it… the smell... it was overpowering!

“Just… buck me already!”

Sunburst gulped again, his heart thumping in his chest as he put his hooves on either side of the tiny, young filly-Starlight under him. She was so small that even if they were both standing, his cock would probably rest on the top of her head! He felt her beautiful wispy purple-green hairs flick along his stallionhood as she impatiently waited underneath him.

“Let’s go! What’s the hold-up!”

Sunburst felt her magic grip under his flare and yank him down toward her fillyhood. He moaned aloud as his drooling flare pulled across her twitching tailhole before feeling the burning heat of her slick filly-cunt against his cockhead. It was obscenely large against her tiny hole, even as aroused and winking as it was.

“...Oh… oh buck… th-that’s bigger than I thought.” Starlight gulped, as the reality of just how young she’d made herself struck her. “...m-maybe we should slow it d-down…”

Sunburst nickered, his nostrils flaring as the scent of young, aroused filly filled his nose. “Oh YEAH? Stop NOW, huh? Once you’ve got me all hot and bothered?” Sunburst growled, “naughty little filly, you need to be taught a lesson.”

Starlight grinned, looking up at the stallion mounting her. “B-buck me, Sunburst.”

Sunburst lit his magic, pulling the filly’s lips as wide as they would go and began to push forward. At first, his fat cockhead only pressed into her swollen hole, mashing itself in what seemed like an impossible task of entering such a tight, twisting, filly-sized love tunnel.

Starlight grunted out, as she felt the strain of her tiny pussy stretching wider and wider, her young muscles opening and shifting in ways that they never had before as the stallion behind her drove his cock against her, pushing the teddy bear trapped between them into the carpet as she was pressed down by his force.

“F-fuck!” Starlight groaned, as she felt her lips about to break and craned her neck back in agony.

“You naughty little filly, let. Me. IN!” Sunburst grunted, accompanying his command with little thrusts, then almost whinnying as he felt the tight, velvety lips slide over the ridge of his flare with a little POP!.

He was in. Or… his tip was in, at least.

It was insane, the tightness was almost painful. Hot, wet, twisting. Gripping and pulsing. He could feel Starlight winking madly as she groaned into the floor loudly, her little hips stretching as wide as possible to allow him into her, almost pinching his fat cock with her vise-like tightness.

“Ungh… buck, Starlight. You’re so damn TIGHT! Try to relax a bit!” Sunburst grunted, stroking her flank with a hoof.

“HNNNNG! A-are y-you bucking kidding me? Y-you’re freaking HUGE.” Starlight moaned, shifting and wriggling to try to make herself more comfortable as her insides desperately tried to adjust around the huge shaft penetrating her.

Sunburst couldn’t help himself, Starlight’s discomfort or not, his biological instincts were taking over, and his hips were beginning to inexorably hump into the little filly, making her squeak and groan with each little thrust.

“Ung. Ungh! UNGH! F-fuck!” Starlight groaned, as she felt the hot meat slide another inch into her, spreading her insides open bit by bit.

“That’s it, Starlight… s-sorry… j-just a bit m-more…” Sunburst’s thrusts were coming more insistently now, the squelching and schlurping sounds of juices being squeezed from the tight filly’s cunt filling the room with obscenity.
Starlight suddenly stiffened, as she felt a familiar bolt of tingling electricity race through her. The thunderclap started in her gut, a painful tightening and twisting of her muscles, before something exploded in her mind, racing out to her horn and her extremities… and her pussy.

“B-buck… I’m… I’m CUMMING!” The filly-Starlight squeaked out.

Sunburst felt the tiny cunt begin to milk and grip at the fat cockhead and inch or two that he had put into her, the spasms coming in powerful waves, one after another… each grip coming with incredible, crushing tightness. He looked down to see Starlight groaning and rolling her eyes, twisting and writhing into the floor.

“B-buck… buck me… buck me Daddy!”

Sunburst whinnied, his stallion instincts kicking in as he stood up, lifting the little filly up from the ground just on his cock, making her eyes open in surprise, before he quickly turned and maneuvered her, still suspended, so that she was placed back onto the couch he had just gotten up from.

“S-sunburst?” Starlight asked nervously, looking up over her shoulder at the snorting stallion.

But Sunburst was totally gone now. Only pure, male, stallion instinct was left. Starlight could only see a heavily breathing, sex-crazed stallion behind her.

“T-take it e-easy S-sunburs- OOPH!”

Sunburst began thrusting into the little filly, his hips and rear legs now driving more powerfully into her, instantly driving another inch of thick, throbbing, veiny horsecock into Starlight’s sopping filly-cunt.

“Oh C-cel… Ungh! Celestia!” Starlight squeaked, as she felt the cockheadslide deeper insider her, bumping against the entrance to her immature womb, sliding past to slam into her fornix, the end of her twisting love tunnel... The end of her entire being.

And yet the stallion kept pushing forward.

“B-buck! Y-yes!” Starlight groaned into the couch cushion, her little hooves kicking wildly at the air as more stallion-flesh was stuffed into her aching pussy. She felt the heavy slap of Sunburst’s large black testicles as they swung against her rear with each of his pounding thrusts, the friction of his medial ridge finally bumping against the outside of her winking filly-clit driving her crazy.

Sunburst exhaled with another snort, as he continued pounding the bottom of the little filly under him, his best friend for years, the same little filly he had dreamed of through highschool and university, his first kiss… his first awkward fondle… now wrapped around his adult cock... and cumming on it… again.

Starlight squeaked, as she felt her body release a splash of filly-cum, splattering back against the shaft driving into her, soaking the heavy balls and flinging her hot spatter all over Twilight’s couch.

“F-fuck! C-cum in me, S-sunburst!” Starlight groaned out, her voice ringing off of the library ceiling.

Then she felt it.

What had already felt big inside her, suddenly became huge… gargantuan. The flare inside her became huge and engorged, and began to throb. Sunburst’s latest thrust was more insistent, driving as deep into her as possible, still unable to get his medial ring inside her. She heard him grunt and groan, as the flare and cock in her tight little body began to throb and jump.

A huge splatter of cum flooded into her. The raw heat was incredible. The first squirt filled her love-tunnel with burning wetness, then another one came, and another. She felt her womb suddenly feeling full, heavy, filled. The unicorn on top of her just grunted and whined as he released rope after rope of of stallion seed into her immature body, which quickly began to overflow.

Spurt after spurt of white seed squirted from around the tight seal of her filly-pussy to his thick cock, splattering noisily to the ground, before finally… exhaustedly… Sunburst slumped to the couch his body weight resting partially on the filly and partially on the couch and let out a hearty sigh.

Starlight giggled, feeling so full and satisfied. She should have done this days ago!

“Th-that… that was… in-incredible.”

Sunburst sighed, looking across at the cute little filly. “Y-yes… it was… I’m s-sorry I was pushing into you… so much…”

Starlight giggled, “Don’t worry about it… this body can only take so much… vitamin D… although… maybe we should try a different… point of entry?” Starlight let her eyes become half-lidded, as she looked over at Sunburst and raised her tail higher, showing her plump tailhole.

Sunburst swallowed nervously, and was about to open his mouth to reply.

A poof of magical smoke exploded next to both of them, and Trixie stepped forward, also in filly-form. “Not fair Starlight! You said that you’d have a turn first, then I could have my turn!”

Sunburst began to sweat, as he felt himself hardening again, still embedded in his filly-friend.

“Oh… oh my…”