twilight is fat and has a big dick. rainbow dash is small and does not. twilight makes it her duty to make her huge with jizz.

“Whoa, Twi!” Dash waggled her legs helplessly as she was levitated up into the air. “What’s this for?”

“Oh, it’s very simple,” Twilight said. She smiled. “We’re gonna get you nice and big.”

Dash stared at Twilight in disbelief - and then really looked at Twilight.

Her belly was her dominating feature. It dragged on the ground beneath her, a gigantic, gurgling ball of flesh that seemed like it would lift her off her hooves if given just an inch or two of extra fat. When she smiled,  her double chins jiggled underneath her flabby cheeks. Each one of her legs was the size of a small tree trunk, and her flank? Rainbow Dash bit her lips, her wings spreading out a bit despite her. That flank was easily the biggest she’d ever seen, and it jiggled madly with the slightest twitch.

Twilight noted Dash’s expression and her stiffening wings. “Well,” she said, her eyelids lowering until she was wearing the sultriest look that Dash had ever seen. “Looks like somepony likes what she sees.”

Dash nodded helplessly. A thin line of drool ran down her chin.

Twilight did a little twirl - though, at that size, “little” was a stretch to describe anything that she did. Each one of her hooves thudded heavily on the ground, and that massive, beautiful flank shook each time one did. “It’s a new look,” Twilight said. “I think I like it, too.

“But,” she said, finishing her turn and grinning at Rainbow, “you haven’t even seen the best part.” And then she plopped back onto her haunches, the ground shaking beneath her as she heaved her hue belly into the air -

- along with something else entirely.

“Mm,” Twilight said. She bit her lip as her fat, throbbing stallionhood climbed even higher into the air. “Feels good to get that out.” As it stiffened, it flopped a few times against her massive, soft belly, leaking precum and inciting a soft moan each time it did.

“You see these balls?” Twilight said once she’d gained back her composure. Dash nodded slowly. She certainly did. Each one was easily a third the size of Twilight’s belly, and they seemed to pulse in time with her own heartbeat. “They’re nice and full with cum - and I’m going to use them to get you nice and big. How’s that sound?”

Dash was nodding before she could even think.

Twilight’s smile widened. “Good,” she said - and then Dash found herself hovering directly over Twilight’s massive horsecock. She bit her lip as the levitation spell slowly lowered her down, spreading her legs wide until she felt its tip just barely poking against her nethers.

“That feel good?” Twilight asked. Dash nodded faintly. “Then how about - “

She let the spell go for a moment, and Dash slid down six inches onto Twilight’s shaft. “ - this?”

Dash groaned in pleasure. “Twi,” she panted. “You’re…really stretching me.”

“Not enough, it seems,” Twilight noted. “That’s just the head. Now, if we go a little further…”

Dash’s eyes bulged out as she slowly slid down Twilight’s dick, impaling herself on the much fatter mare’s throbbing horsecock. Soon, she could feel Twilight’s giant, flabby belly against her back. She was sinking deeper and deeper into that stomach with each bit that she inched down onto Twilight’s cock. She grunted, struggling to pull herself together.

And then Twilight smirked with her flabby cheeks and lifted Dash back up again - and smashed her back down.

Rainbow Dash grunted, groaned, and writhed as Twilight, too fat and heavy to fuck her herself, instead used her magic to make her into a giant cocksleeve. Rolls of Twilight’s fat jiggled whenever she bottomed out inside of Rainbow Dash, Rainbow’s stomach bulging out each time with the flared head of Twilight’s cock. She could already feel her stomach filling up with its leaking precum. Had she not been nearly out of her mind with pleasure as Twilight fucked her senseless, spreading her legs and cunt wider than she’d ever spread them before, she might have been concerned about the volume that Twilight’s actual orgasm could put out.

Soon enough, Twilight felt the edge drawing closer. “Mmff,” she grunted, sweat sliding down her flabby chest and belly as she thrust Rainbow down her cock again and again. She moaned, feeling the tightness come to a peak, her enormous, sloshing balls actually retracting a bit toward her body -

Then the tension vanished and cum flooded out of her in a giant, glorious spray of semen. Her cock throbbed and pulsed and swelled inside of Rainbow Dash, literal liters - no, gallons of seed erupting inside of the thin, lean pegasus.

Well, formerly lean. Dash let out a groan as she felt her belly start to bloat. More and more cum flooded into her from Twilight’s orgasm, filling her up until she could feel the skin stretching tighter and tighter beneath her hoof. And still, Twilight came. The sight of her own burgeoning belly was enough to send Rainbow over the edge, and so she came too, her body convulsing in pleasure and her cunt tightening around Twilight’s massive member as sticky, sweet juices ran down its length.

More and more cum flooded into Rainbow Dash until her belly protruded obscenely from her abdomen. Soon, it was groaning and sloshing but still growing, swelling and stretching until it was nearly as big as she was. She could feel all of that warm, thick cum inside her, sloshing and shaking about each time she moved, with still more and more joining it.

Finally, Twilight finished, the flood slowing to a trickle. By now, Rainbow Dash was a blimp, nothing more than a pony attached to a pony-sized balloon full of hot mare spooge. Slowly, her breath steadying, Twilight lifted one flabby hoof and patted the side of Rainbow’s round, tight belly.

“See?” she murmured, loving the feel of her own fat beneath her arm. “Nice and big.”

Rainbow just groaned in agreement.