Pinkie Pie, Twilight Sparkle decided, had a marvelous flank.

She’d noticed it before, of course, but somehow had never really had devoted the time to really ponder it properly. As Pinkie’s marefriend, Twilight had always taken for granted every part of Pinkie’s body: her coat, soft like cotton; her thighs, warm and sproingy; her belly, soft like a marshmallow—probably from eating too many of them, come to think of it. She’d explored Pinkie’s body many times, and Pinkie had explored hers many times in return.

But this was different. Somehow, Twilight had never really seen Pinkie’s flank before. Not like this.

It was a marvelous rump, that much was sure. It had a nice curve, pushing out from her hips by a few inches before tapering back into her smooth, sleek waist. Each one of those cheeks was a full, plump sphere; Pinkie’s Cutie Marks, Twilight estimated, were easily half again as wide as her own. Twilight thought about recording her thoughts on paper, but decided against it. This research, she decided, had to be done in the field.

It wasn’t hard to see where all the sweets went. Pinkie’s rear was nicely rounded, and soft and plush to boot. Twilight had curled her hoof around it on more than one restful night, but she suddenly felt the strongest urge to go up and lay her head on it. To nuzzle it, to bury her face in Pinkie’s rump, to inhale her sweet feminine scent and to let Pinkie’s plump cheeks surround her own.

What pony had a flank like Pinkie? Rainbow’s was lean, sculpted from years of hard flying. Applejack’s was thick and corded, accompanied by a pair of applebucking hips wider than any Twilight had ever seen. Fluttershy’s, too, was surprisingly plump, and Rarity’s was always sleek and brushed to perfection.

But none could compare to Pinkie’s—it was, it had to be, a perfectly plump plot. Twilight felt herself sway lightly on her hooves, her thoughts spinning in time with the heat growing between her legs.

Each cheek—so perfectly rounded. Twilight pictured it now: Pinkie walking, her buttcheeks sliding against one another, slapping against the tops of her thighs with every step. Her Cutie Marks rippled like water at the slightest disturbance; when she’d stop short, her whole body would quiver, her ass retaining its inertia and pushing the rest of Pinkie’s body forward.

Her ass. Twilight tasted the word and shivered. Such a dirty word. Such a fun word. And so deliciously appropriate.

Pinkie had a wondrous, glorious ass. There was no other word for it. Even now, just facing it from across the room, Twilight found her eyes drawn to it like a magnet. She wasn’t sure what Pinkie was doing, or why. All Twilight knew was that a standing-still Pinkie was one that would give her ample time to ogle that beautiful rump, not to mention one that wouldn’t even notice her doing so.

Twilight took an unsteady step forward. Even now, Pinkie’s flank was wobbling slightly, as if somepony had just smacked it and left it to jiggle like a plate of jello. Twilight would almost swear that Pinkie’s ass—she shivered again with pleasure—had grown since they’d begun dating. All of those cupcakes had to go somewhere, of course. It seemed that all of that sugar, all of that fat, had just gone to padding out that ponderous, plump pink plot.

It wasn’t often that ponies wore clothes. Pinkie was often one to dress up for parties, though. The last time she’d done it, it’d been for a sports-themed cuteceñeara. Twilight recalled the way Pinkie had worn those skintight shorts with another pleasurable shiver. They’d clung tight to her plump pink body, hugging her curves. Pinkie's thighs, which touched all the way down to her knees, had bulged, packed tightly into shorts. Every time Pinkie had so much as twitched, more of the fabric had ridden up to show off her fat, rounded flank. Twilight realized, somewhat guiltily, that she hadn’t been able to resist ogling Pinkie then, either.

But how could she resist? Pinkie’s rump was halfway up her neck, for goodness sake! Those fat, globular asscheeks rolled across each other whenever she walked. Watching her massive rear ripple like jello with each jiggle—now that was an experience. More and more, Twilight recalled herself finding excuses to walk behind Pinkie, watching the shifting of her muscles compress the globes of meat and forcing them up and outward, then down and underneath with each step.

A few beads of sweat had accumulated on Twilight’s forehead. She wiped it away, and realized that she was breathing heavily. The heat within her loins had grown into a furnace now. Mesmerized, hypnotized by Pinkie’s rump, Twilight took a small step forward, then another. She felt lost, captured by the gentle sway of Pinkie’s hips, by the enticing softness of those large, round pillows.

Before she knew it, she was face-to-cheek with Pinkie’s rump. She took a deep breath, inhaling Pinkie’s scent. Then, on reflex alone, her hooves darted out to seize hold of Pinkie’s prime ass.

Twilight shuddered with pleasure. She felt like her hooves were melting into Pinkie’s flanks, the other mare’s abundant buttflesh swallowing up her hooves. She could feel them sinking deeper, prodding against the plumpness of that succulent rump, and sighed contentedly. Now this was a butt to be proud of.

“Oh, hey Twilight. Is it ‘poke Pinkie’s booty’ time already?”

Twilight started. For a moment, she’d forgotten that Pinkie’s flank was in fact attached to the pony herself. “Oh. Uh, sorry, Pinkie.”

“Don’t be!” Pinkie’s head whirled around to face her. Her grin stretched all the way across her face. “I’ve been waiting for it!”

“Waiting…?” Twilight blinked, then tracked Pinkie’s gaze back up to the clock. “Wait. You knew—”

“Well, duh. I was even watching the clock to see when you’d be ready!” Pinkie nodded toward the clock on the wall, and Twilight blinked.

“I even ate an extra plate of cupcakes for lunch just for you!” Pinkie’s eyes fluttered, and for a moment, there was—somehow—a hint of seductiveness in that bright, cheery gaze. She reached back with a hoof and gave her flank a nice, long squeeze. Twilight felt a bead a sweat dripping down her forehead at the sight of Pinkie’s hoof-full of rump. Pinkie just nodded sagely and patted her flank. It jiggled and wobbled magnificently, padded absolutely to the brim. “Nice and soft, just how you like it!”

Twilight restrained the urge to sigh, even if good-naturedly. Pinkie Pie would be Pinkie Pie, after all. And if Pinkie was offering her the chance to fondle her—wonderful, massive—flank, then who was she to refuse? Happily, Twilight clamped down on both of Pinkie’s oversized Cutie Marks and gave them a healthy squeeze.

As Pinkie melted beneath Twilight’s hooves, Twilight found herself getting even more turned on. Massaging Pinkie’s rump was like squishing a pair of marshmallows; her flanks were so thick, so plush, so warm. She took a deep sniff of Pinkie’s sweet, sugary scent and actually groaned when her loins twitched in response.

“You like touching my flank, don’t you Twilight?” Pinkie said brightly.

Twilight bit her lip, then smirked. “Whatever gave you that idea, Pinkie?”

“Oh, just the way you’re poking around every inch of my butt.” Pinkie flexed her rump, her buttcheeks bouncing slightly. “I think you really like it—but just how much?” She shot Twilight a sly grin.

“I love it,” Twilight said. “It’s—well, you just have an incredible flank.” Her cheeks flushed a bit, but she kept rubbing Pinkie’s Cutie Marks.

“Incredible?” Pinkie said. “More incredible than Princess Celestia’s?”

“Pinkie!” Twilight’s cheeks burned. “You shouldn’t talk about the Princess that way.”

“Oopsie.” Pinkie giggled, then waggled her ass beneath Twilight’s hooves. “I guess my booty’s the only flank you need, huh?”

Twilight’s mouth went dry. She grunted softly at the sensation of Pinkie’s sea of assflesh quivering beneath her hooves. “Mmph. I mean, yes.”

“I like it a lot too,” Pinkie said. “I’ve eaten a lot of cupcakes to get it this big. See them all spread out? They make my flank nice and soft.”

Twilight’s hoof sank a good inch into Pinkie’s ample buttflesh. Unf.

“Give ‘em a poke,” Pinkie said. “Feel how soft they are.”

Twilight gave Pinkie’s Cutie Marks another prod.

“No, not like that, silly,” Pinkie blew Twilight a raspberry. “Really poke ‘em. Show me how much you love them!”

Twilight poked Pinkie’s flank a bit harder. She shivered with pleasure at the sight of Pinkie’s flank quivering like a bowl of jello. Pinkie groaned, then said, “Harder, Twilight. Harder!”

Twilight finally got the message. She pulled her hoof back, uncertain of how hard she should make this—and then smacked Pinkie across the rump with the back of her hoof. Pinkie squealed happily as her twin globes bounced and smacked together from the force of the impact. The aftermath of her spank sent Twilight’s libido into overdrive; the heat between her legs was almost unbearable, and she was beginning to leak her arousal onto the floor.

She whimpered softly. She’d rarely felt a greater need. And Pinkie’s flank—that glorious, marvelous flank—was right there in front of her.

Before she knew what she was doing, she’d planted a kiss on Pinkie’s wide flank. From there, she slowly licked her tongue up Pinkie’s Cutie Mark as she squeezed and kneaded the chubby mare’s flank. Pinkie’s giggles mixed with a pleasurable groan as Twilight’s hooves went to work on her flank.

“Ooh, Twilight,” Pinkie panted. “You naughty filly, you.” She waggled her buttcheeks beneath Twilight’s nose. The scent of her marefriend’s own arousal hit Twilight in the face like a freight train. Pinkie’s feminine lips were winking madly, inviting her closer. Twilight’s nose twitched at the sight of a single drop of liquid streaking down the inside of Pinkie’s thigh. Mesmerized, hypnotized by Pinkie’s chubby, lustful labia, she leaned down: closer, then closer, then closer.

“Go on, Twi,” Pinkie murmured. “That’s prime real estate back there! All yours—ooooh.”

Twilight had already seized the opportunity. Pinkie groaned happily as Twilight’s tongue dragged across her outer lips. The sound of lips smacking filled the air, Twilight kissing Pinkie’s inner thighs before rubbing her snout along her marefriend’s slit.

Pinkie was panting happily now, her plump butt bouncing and flexing with eagerness as Twilight nuzzled her most private parts. Twilight’s tongue darted out—first hesitantly, then warmly, sliding into Pinkie’s marehood with all the taste and sensuality she could muster. Pinkie moaned, her whole body shuddering as Twilight lapped at her core, her tongue massaging her hot, velvety insides.

Warm juices dripped down from Twilight’s own aching marehood as she attacked Pinkie’s with tongue and lips. Her horn, purely on reflex, lit up with magic. Twilight moaned as she masturbated with her magic, teasing her own needy pussy even as she tended to Pinkie's. Even without any additional stimulation, she felt like she was turned on enough to cum at any minute.

She wriggled her tongue inside Pinkie’s marehood as her hooves continued to work on the other mare’s rump. She squeezed, massaged, and teased Pinkie’s ample flank, then squeezed her plush buttcheeks around her own face to fill her muzzle with Pinkie’s sweet scent. “Ah—” Pinkie groaned, her breathing growing more labored. Twilight increased the intensity of her assault, wiggling her tongue inside of Pinkie’s marehood as her hooves did double-time on the well-endowed mare’s assets. Twilight was groaning into Pinkie's snatch, the other mare's secretions dribbling down her cheeks as Twilight approached her own peak. “Oh, yes. Ooh. Twilight—ah—ah—aah!”

Pinkie’s inner muscles clamped down around Twilight’s tongue, her lips winking. Pinkie squealed as Twilight lapped at her spasming insides, sending her further into her peak. Pinkie whinnied and jerked wildly. Twilight kept licking, then latched onto Pinkie’s labia with her lips and started sucking. Clear marecum, Pinkie’s sweet honey, streamed down Twilight’s chin. She lapped it up, then swallowed Pinkie’s taste as Pinkie’s tail twitched wildly above her head. Twilight's own orgasm followed soon after; with a long, throaty moan, she came with her muzzle still buried between Pinkie's rump. Stars burst in front of her vision, the heat between her own legs becoming an inferno as she went over her edge. Twilight's body shook, spasming as she came, her horn flaring bright purple as her wetness seeped out over the floor.

Before long, Twilight’s whole muzzle was drenched in Pinkie’s juices. Smacking her lips, she slowly pulled away. Both her hooves were still firmly clamped on Pinkie’s oversized rump. Pinkie was panting softly, her body still trembling.

A worn-out smile on her face, Pinkie turned back over her shoulder and beamed at Twilight. “Wowie,” she said. “You really like my flank.”

Twilight gave Pinkie’s Cutie Mark a big squeeze. “Whatever might’ve given you that idea?”

Pinkie winked. Her head whipped down between her front legs, and she stared back between her hind legs at Twilight. Twilight blushed when she realized just how big of a mess her own arousal had made beneath her.

“Oh, nothing,” Pinkie said. She had that sing-song, teasing quality to her voice. “Just that you seemed to like touching it an awful much!”

Twilight giggled. “Yes, Pinkie,” she said, giving Pinkie’s rump a final squeeze. “Yes, I did.”