Rainbow Dash Breast Expansion. Maybe of her in a bikini at a beach.

“Now this is more like it.” Dash grinned to herself as she plopped herself down on her beach chair and lowered her sunglasses over her eyes. “No Pinkie to distract me now. Just me, the sun, and six hours of no work in sight.” It was pretty clearly time - at least to her - to catch up on some valuable napping time.

From the second she’d walked onto the beach, though, Dash had been the center of attention. She was a slender, boyish mare in a lot of ways, but her slim, lean body had caught the attention of more than one stallion (and mare) around her. The skimpy bikini didn’t hurt either; while Dash had never had the biggest bust, the little thong and bra left very little to the imagination. Dash was particularly proud of that. She’d bought them at some trashy store in Manehatten purely to see the look on Rarity’s face when she put them on, and had never regretted it.

As Rainbow Dash left off to catch up on her Zs, though, a few of the more perverted onlookers noticed something happening - specifically to her bust.

With each rise of her chest, her breasts lifted a big higher into the air. With each fall of her chest, they hovered in the air, perhaps even jiggled a little - and completely failed to lower back down.

Only a pony with a sharp eye would have noticed at first, but after a few minutes, there was no mistaking it: Rainbow Dash’s bust was getting bigger. With each exhale, her chest swelled up a little bit bigger, soon leaving behind her A-cups and straining against her skimpy little bikini top with two mammaries that were rapidly approaching a C-cup.

She moaned softly in her sleep and squirmed slightly in place at the slightly heavier weight on her chest. Her two boobs jumped and jiggled slightly, then seemed to swell even larger in response.

Fluttershy herself was “only” a D-cup, but Rainbow Dash looked fit to surpass her in that regard - and she wasn’t even awake. A cocky grin fluttered across Dash’s sleeping face as she got herself comfortable, her back pushing up against the warm chair’s back as her growing breasts pushed down against her chest.

By now, the poor little bikini top was clearly working overtime, with Dash’s jugs having swollen to the size of small melons and stretching it nearly to the breaking point. More than one stallion on the beach was inconspicuously stroking the space under his bathing suit, and more than one pondered going over and trying to introduce himself to this wonderfully-chested mare.

All, however, settled for simply watching. At least they all had a good view.

Dash’s nap was finally interrupted when the bikini finally gave up on life and snapped with a loud twang. Her eyes shot open - only to have their sight blocked by what appeared to be two massive mounds of soft, blue flesh quivering on her chest. She hesitantly reached up to poke one and moaned as her sensitive breasts started jiggling wildly at her touch.

By the time she’d started to run her fingers over them, eyes still wide but soon clouded with lust, each and every stallion had given up on being inconspicuous. And the very thought of trying to re-cover her chest - of maintaining some sense of dignity over lust - never even crossed Rainbow Dash’s mind.