Rainbow Dash wiped her brow, drenched in sweat after a long jog. She always looked forward to her morning runs, even if no one else wanted to wake up early enough to join her (Well, Fluttershy did once, but she passed out on the first mile.) She did some stretches, ready to circle back home, when suddenly she slipped, almost falling onto her face, as she felt her shoe go flying off of her foot. She knew she had tied them, so what had happened...?
"Ah, crud." Rainbow sighed, finding the shoe. While the laces were still neatly tied, the bottom of the shoe had completely torn open, allowing the thing to be swung off of her leg. This wasn't surprising, her running shoes were "well-loved," to put it kindly, and she'd meant to replace them, but kept putting it off. But she couldn't head home like this...
Taking note of the area, Rainbow realized she wasn't too far from her favorite sports store. Walking there, she smiled at the cashier as she walked in, making her way to the shoes section, and grabbing the first thing that fit. Lacing it up, she looked up at an advertisement on the wall. It depicted a girl downing a bottle of something called "MAX BUST SPORTS DRINK!" More specifically, she found her eye drawn to the girl's chest. She didn't think it was possible to be bigger then Pinkie's massive E-cups, but the girl on the poster sported a chest even bigger, only barely fitting into a sports bra. Dash couldn't help but glance down at her own chest, tiny A-cups. She wanted to say she didn't care about looks, smaller boobs meant less wind-resistance when she ran, but sometimes (especially around Pinkie or Fluttershy,) she couldn't help but feel self-conscious about her distinctly un-feminine body.
"It'd be a pain in the ass to run with those..." Rainbow joked to herself, standing up and taking a few steps in the new shoes, checking their fit. During so, she instinctively imagined a large bust bouncing with every step. She shook her head, trying to to stop her brain from thinking about big boobs.
"Hey, are you alright?"
Rainbow blinked. She'd gotten to the register without realizing it, and the cashier was looking at her strangely. It was then that she realized how exhausted she looked. She'd run all the way there, after all, and then had to walk an extra block or two to replace her shoes, and with the adrenaline of the workout wearing off, she was realizing just how thirsty she was.
"Yeah, I'm good." She said, checking the drink cooler at the register. She'd normally get a water, but Fluttershy had given her an earful about the unethical water industry or something, no soda of course, she was going to be running back to campus, so what would she...
She stopped, catching a bottle with a familiar logo. Max Bust Sports Drink. She wasn't really going to get one though, was she? Just because an ad had a sexy girl on the poster didn't mean she would...
---
"Oh, this just came in! Tell me how it tastes!" The cashier said, ringing up the bottle of Max Bust, Grape Flavor.
"Yeah, okay." Rainbow sighed.
---
Stepping out of the store, Rainbow downed the entire bottle before tossing it into the trash, alongside her old shoes, and began her run back, unaware of how her chest began to bounce a little more with every step...