A little whimper escaped Applebloom’s throat. Big Mac paused, stopping from lowering her down further. He glanced up, meeting her big, purple eyes.

“Y’alright, ‘Bloom?” Mac said softly.

She nodded. “Y-yeah.” A glance downward, though, accompanied a little quiver in her voice. “S’just, uh, really big.”

“Eeyup,” he said. “That’s the idea.”

The little filly in his hands took a deep breath. Then, with a little nod, she offered him a grin. “Okay,” she said. “Let’s - ooh.”

Her little hind legs wriggled, her flanks flexing as the first inches of his great black rod pushed her legs further apart. Applebloom groaned, sighing in tightness and what Mac hoped was pleasure as another inch of his fat cock slipped into her virgin fillyhood, spreading her wider and wider than any explorations with her hoof had ever delivered.

A shuddering sigh was the only sound in his ears as he kept lowering her down, gently, inch by inch. Applebloom’s little hooves wrapped around the growing swell in her belly, and she groaned, rubbing the bulge his cock made in her as his fingers tightened around her flanks.

“Nggfh,” she mumbled. “S-so full.”

He blushed. “Eeyup.”

With a cheeky grin, she squeezed one eye open and grinned up at his hulking form. “S’why we call you B-big Mac, right?” She gave her belly a little pat.

He chuckled. “Guess so.”

She squirmed atop his member. It looked like she’d accommodated to his gargantuan size; by the little pants and breaths she was making, it sounded like she was psyching herself up for more. Then - “Why’d you stop?” she asked.

Mac regarded her with a concerned look. “Just - “ He bit his lip, frowning. “‘Member our rule?”

She bobbed her head pleasantly. Even as she replied, though, her hind legs were wrapping around the solid base of his turgid shaft, making a tiny effort to rub her little body up and down the length of the pillar of meat impaling her. “Don’t tell Applejack.”

He nodded. “Eeyup.” A little smile touched his lips. “Now - y’all ready?”

She was suddenly perfectly erect on his cock, hooves wrapped tightly around the flare-shaped mound he’d left in her middle. “Yeah!”

He grinned - her enthusiasm was infectious sometimes. Then, with a grunt, he held his little filly of a sister close to his chest and turned. With an exhale, he released his cock from his grip and let it swing down onto the bed - taking Applebloom with it.

She hit the thick cotton quilt with a gentle thump, the mattress shaking more with the weight of his mast than her body. She lay back with her big eyes blinking up at him, hooves drawn up to her chest. Beneath him, it was so clearly apparent how much smaller she was than him: a tiny, delicate little pony wrapped around a cock big enough to outweigh her - a cock owned by a male three times her height and ten times her weight. He shivered as a current of lust turned hot in his belly, and his thirty-inch biceps flexed.

With a low, shuddering gasp, he began to draw his hips back. Applebloom inhaled sharply when his thick flare slipped from her pussy, leaving its weight perched atop her delicate lips. “W-why’d you take it out?” she whimpered. She squirmed against the weight of his big hands keeping her firmly pressed to the bed. With his hands wrapping around her flanks, his thumbs easily reached around half her belly, even as her hind legs kicked needily in the air below him. “P-put it back in.”

Big Mac grinned. Slowly, he see-sawwed his length between Bloom’s spread legs. She whimpered, flexing her core as his slit drooled tablespoons of thick, musky pre onto her chest. Then, with a grunt, he pulled his hips all the way back - and thrust himself back inside.

Applebloom squealed - and then shuddered, hooves flying back to the bump in her belly. She moaned aloud, wriggling as Mac began to piston his weight forward, then back. The bulge at her midsection receded, then swelled, each thrust stretching her pliable hide even further than before.

“Like that?” Big Mac grunted.

Bloom whinnied loudly. “Y-yeah! Just - like - ayiee!”

With a full-bodied shudder, her every muscle flexed. Her back arched - and, panting, squealing, she came. Big Mac was grinning ear-to-ear as she came back down, sweat rolling down her face. He’d just given his little sister her first orgasm.

And there were many more to come.

With either hand covering the entirety of her flanks, he started thrusting harder - faster. More and more precum gushed from his shaft, his monstrous arousal barely under control as he rutted his baby sister like a cocksleeve. Stretched out beneath him, so tiny and light between his hands, she might as well have been - barely a condom for his throbbing manhood. More and more pre flooded into her, leaving her belly a bit rounder every time he pulled his weight back, her hide further stretched around the liquid essence his lust left inside of her.

Her hind legs curled around his shaft, even as her forelegs wrapped fully around the bulge in her belly. Mac groaned, snorting and grunting as Applebloom’s little legs jerked him off with every downthrust, his massive tool barely fitting between the full reach of her limbs. His great muscles flexed, his organ pressing Bloom harder against the bed as his thrusts grew faster, stronger, and more wild by the second.

The very frame of the bed creaked and groaned, mixing with her little pants and moans as his fat testicles smacked against her rump with every thrust. She writhed and groaned as he rutted her with all the force of a piston, in and out, in and out, in and out -

She came again. And again. Bloom’s little head was flung back, her eyes wide, muzzle gaping as climax after climax wracked her body. Her inner walls were so tight, her pleasure so pure. Big Mac’s nostrils flared, and he strengthened his grip around her belly. His thumbs pressed in tight against her hide, squishing against the soft flesh of his cock inside her. He could feel the pressure mounting, the oncoming tide swelling, until there was nowhere left for his pleasure to go but out -

With a pure, primal roar, he released his own climax. A tsunami of his seed rushed out to flood inside her. In a blink, his orgasm had bloated out her belly; in another, it had flooded into her womb. Applebloom whinnied beneath the weight of his cock pressing down against her womb, each wild jerk of her big brother’s body only pumping her fuller of his seed. Her hooves flew to her belly, and she moaned as he kept jizzing, releasing more and more of his spunk until she looked as pregnant as a mare thrice her age.

Finally, his rush of cum ended. Big Mac flipped his weight and flopped back onto the bed. Above him, Applebloom panted and groaned, trembling as she struggled to fit her forelegs around a cum-belly that was larger than she was. He could smell his own musk on her - could see her gut wobble and slosh as her little body struggled to hold in the massive ocean of seed he’d left inside of her.

Slowly, panting, but cooing with pleasure, she bent forward until her cheek was touching against his chest. His cock softened inside of her, allowing her to move more freely until she was hugging his great, naked pectorals, her squishy belly rubbing against his abs.

“M’I gonna have your babies now, Big Mac?” Applebloom asked sleepily.

He chuckled, and reached up to tousle her mane. “Y’might, ‘Bloom,” he said. He sighed, grinned, and stroked her big, cum-stuffed belly. “Just might.”