When making a welcome back gift for Rarity, Twi accidentally turns herself into panties. Whilst away, Rarity has picked up a big eating habit/desire for full figuredness and Twi is now much too small. Able to get them on but hard to get off, Rarity reasons she'd reach her target size if she just gained till she bursts out her clothes. Weight gain and inanimate transformation.

“Ungh!” Rarity grunted. Both her hooves were wedged tightly into the waistband of her panties, and she kicked and groaned as she struggled to get them off. Unfortunately, her fat, flabby thighs rolled over her hooves every time she tried to push them down. Her enormous ass had already stretched the panties as far as they could go - there was no widening them anymore.

“Bother,” Rarity huffed. She took a moment to wheeze, her big, round belly moving in and out with each breath. It appeared that her desire for a fully, more bountiful figure had come at a cost. While away, she’d absolutely adored the sensation of filling out her clothes, of stretching them until they could stretch no more. Thin was out, she’d said, and thick was in!

But it looked now as though she’d perhaps gained too full a figure. Rarity pouted. She’d managed to get Twilight’s gift on just fine, but removing it seemed to be beyond her at the moment. She truly loved her new panties, especially the little frills that looked so positively dainty besides her full, flabby thighs and rump, but if she couldn’t get them off, then there’d clearly be a problem.

She clucked her tongue in irritation, pondering. Then, a thought occurred to her. A wicked smile spread across Rarity’s face, and she went to the kitchen.

Stretched tightly around Rarity’s waist, Twilight could only watch in mute horror as her friend approached the refrigerator. Rarity’s giant, swaying belly was already gurgling, growing louder and louder each time it smacked against its owner’s thighs. She wished she could have spoken - to teleport away - to warn Rarity or just to get out of this mess entirely. But with her horn gone and Rarity’s enormous, wide-loaded ass stretching the fabric of her “face” to its limits, there was nothing she could do.

Rarity finally plopped down at the table. Her belly jiggled mightily at the impact, and when she leaned forward to reach her prizes, it squished against the table. In fact, it seemed that her belly was so wide that her hooves could barely reach her food!

Fortunately, Rarity was a unicorn. She let her hooves instead drop to her belly, massaging and kneading the poor empty thing, and let her magic do the work. A dainty slice of chocolate cake cut itself from the rest of the platter, hovered into the air, and disappeared into Rarity’s waiting gullet.

For Rarity had come up with a plan. As much as she loved Twilight’s gift - really, it was wonderful, and the tightness she felt across her flank had made her feel the sexiest she had in ages - it seemed to her that the only way to remove it was to force it off. To snap out of it, quite literally.

She stifled a giggle, instead opting to shovel another slice of cake - this one not so dainty - down her throat. Her stomach slowly bloated as she finished the rest off, until it was bulging a good inch further into the table.

Rarity picked up one of her oversized flanks and peered at the panties. By now, they - that is, Twilight - had been stretched so much that they seemed like little more than a tiny thong! But Twilight groaned internally as a fold of Rarity’s fat folded over her “face” once more, blocking her vision and filling her nostrils with a sweet, aromatic musk.

Rarity sighed and let her fat flank fall back to the chair, shaking it slightly. Not enough? Not to worry. There was plenty more to help her grow.

She gulped down two whole pies, consumed an entire pound of leftover pasta as if it were nothing. She dumped a half-gallon of mashed potatoes down her throat, and washed it down with a full gallon of milk. Soon, her chair was actually being pushed back from the table by her ever-expanding belly, and its legs were actually beginning to creak beneath Rarity’s enormous weight.

In a moment of self-indulgence, Rarity took hold of her taut, yet soft gut in both hooves and squished it gently. She moaned as it squeezed - and so did Twilight, at least mentally, as Rarity’s motion caused her to spread her legs (and therefore, her ass) even wider, which only stretched Twilight even more.

Rarity massaged her full belly for a few more moments, then glanced back over her thick shoulder at her ass. By now, it must have been over two feet wide, and was more than overflowing the sides of her chair. She grinned and smacked her belly, loving the feeling of vibration that spread through her body.

She frowned at the panties, though. They were stretched to their max - barely a g-string now, cutting right through her giant asscrack and squishing her bountiful rump - but they were somehow still holding on. Just barely, though. With a smirk on her face, Rarity delicately hovered a cupcake to her mouth, and swallowed it whole.

The chair shattered beneath her. Her panties - Twilight - snapped with a sound like the crack of a whip. And Rarity hit the ground and groaned, her massive belly gurgling with the wonderful, insurmountable feeling of being full.

“Well,” she murmured, patting her stomach. “That certainly did the trick.”