Wanting to finish this as soon as possible instead of dragging it out, I dropped to a squat like a lowly servant, and abruptly found myself at eye-level with my sister's nude bum cheeks. I'd gotten glimpses of them before, of course, every time Mia arrived home from practice in shorts, often stripping right down to her underwear without giving a shit who saw her. However, there wasn't even the guise of thin panty fabric now to conceal the magnificent geometry. I saw every cell of it all: the immense tanned twin buttocks, the long valley of her crack between, and the hints of hidden sculpting beneath every time her flesh twitched. The whole of it was more than large enough to cover my head and then some, which of course I'd experienced multiple times while Mia sat on me in her sweaty shorts following a hard scrimmage. Now, I'd have given anything to have those filthy garments back on her again, if only to separate my eyes from the direct line to my sister's prodigious bubble-rump.

            "What are you waiting for? Start pulling on it," she commanded, stretching the elastic waistband in my direction with the back of her thumb. "We haven't got all day."

            Gingerly I took hold, feeling through the fabric for whatever problem I was 99% sure wasn't actually there. All the while I tried to avert my eyes, but it was impossible to work without looking at my sister's shorts, now hiked up around her thighs, which inevitably meant the lower quadrant of her looming naked ass hung in my peripheral. Every subtle move I made, tugging at the rim of her shorts, caused her bare thighs and tush cheeks to quiver anew. There seemed to be no problem here, but Mia hadn't said I could stop, which meant I was not free to let go yet.

            Inches from my face, a time bomb was ticking. The acidic grumbling within Mia's digestive tract, which was usually happening at all times, halted briefly, before coming back with a roiling vengeance. It sounded like caustic liquid flowing and bubbling up in a pressure cooker. Her gut growled louder, building toward a crescendo. Every muscle in Mia's backside tensed, then relieved, loosening the swollen cellulite and the tightness of her crack for better dispersal in the coming seconds.

            My skin crawled; my nostrils pre-emptively narrowed in defense, even before I could detect the first brackish note in the air. For a fleeting moment, I considered diving toward the door, regardless of the flack I'd catch. Mia anticipated this wish, however, and reached behind her back at lightning-speed with the same precision she used on the court, clasping the back of my skull in her palm and clawing her fingers out to ensure I couldn't face anywhere but directly toward that unholy bass. I couldn't say whether I heard the ear-splitting clap of the ejecting fart first, or instead had my airway infected by the noisome gristle-clotted odor. What struck the greatest blow in that initial blast, rather, was the gust of muggy, putrid anal-wind itself, concentrated like a gale-force tempest. It instantly watered my eyes, turned my cheeks rosy, and even blew my hair back. Then the uncomfortable heat, the wretched din, and the poisonous bean-and-intestine reek all hit at once, lingering in my senses as Mia kept my head in her grasp where I couldn't escape. Tears flowed down my cheeks and my throat burned while the burgeoning stink filled in my lungs, the same aroma I'd noticed on the way upstairs, only quadrupled in punch. Her ass tremored seismically from the strength of her belly-laughter at my expense.

            How had it come to this? I guess in retrospect some of the warning signs were there long before. No, I couldn't have predicted Mia's growing evolution in a million years, but my sister's always had a predilection for her butt's potential as a tool. It started when we were young. Mia always laughed the loudest at fart gags in movies and TV, imitating the noises and blowing raspberries in my face. She started using pull-my-finger jokes at every family gathering, buying whoopee cushions and other prank items before she could generate her own GI-responses loud enough to count. Then, as an adolescent, she must've spent time developing the kind of muscular and bowel control necessary to fire pungent farts out of that once-petite ass, first merely strengthening what she already had brewing inside, then soon learning how to blast them on command, throughout the day and in numbers that surely distressed her stomach, but definitely distressed everyone around her even more.

            At first Mia only used this power of hers to annoy me, like any little sister would, and I just brushed it off, though as time went on, and she dropped more and more silent killers in my airspace, eventually getting comfortable enough to actually be amused when she noisily let out a thunderclap of a fart, it became harder to believe that it was just a natural byproduct of her diet. Her eating habits, coincidentally, had started incorporating more meat and protein products, burned off by her metabolism and intense exercise, and transformed directly into gassy ammo without affecting her impressive physique. It was truly astounding. I hate to think this, but objectively, Mia falls into the category of conventionally attractive young women, with her plush assets, shapely athletic figure, piercing eyes, and sleek black hair always tied back in a ponytail; you don't usually imagine most girls like that having such fun, and even taking pride, in their capacity to unleash a torrent of rancid, eggy farts that could cloud a whole room and sink into the very fibers of the carpet. But Mia isn't most girls.

            Soon mere annoyance at her constant fart warfare turned to outright deep-seated dislike, even apprehension that when I saw my younger sister coming, I was in for some breaking wind. And I usually was. It became a Pavlovian response, only in the worst way possible; instead of anticipating reward, I'd see Mia coming my way and retreat elsewhere, like a peasant genuflecting out of the queen's presence. Often, she'd follow after me anyway, giggle and wink, then let rip a whopper of a smoke-bomb. And that was all even before she'd grown a single inch higher than five-two. At least then, I had the benefit of a height advantage, thus somewhat protected from the line of fire. Now, I'm not so fortunate, since my face is closer than ever to those bouncy cheeks the higher she rises, and only getting closer by the day. Sometimes, like right now, when she's just intentionally spewed a warm, fusty, dairy-flavored cloud right into my face from a few inches away, it feels like we couldn't possibly get any closer. Then again, I'd probably just be jinxing myself to believe this is as bad as it can become.

            "I think you fixed it!" Mia concluded, even though I hadn't done a damn thing. Her hand swapped from holding the back of my head to the front, pushing off of my nose with her palm so I fell flat on my back. From my low vantage point, I watched my sister, looking taller than ever, yank her underwear and booty shorts up those golden pillars of her legs, and witnessed the fabric stretching close to the point of breaking as she pulled those paltry shorts over those roomy posterior cheeks. Happy with their placement, she gave her butt a smack that would've left me with a black eye if I was still up close. The accompanying jiggles were hypnotic. Mia, satisfied, turned round and scooped me back to a standing position with one pull. My vision was still blurred due to the stink-induced tears welled in my eyes, and the general sting clouding the bedroom as a raunchy, vaguely-feminine smog. The second we opened that door, the rest of the house would adopt that rankness, too.