Their prior squabble had instantly become trivial, as a much more important matter was on both of their minds. Jackie jumped to her feet, and nodded for him to stand up too. He was just as curious (and slightly nervous) as she was, so he got up and stepped up toe to toe with his sister before she even asked him to. Just a few minutes ago, Denver had been 5’8, and Jackie was 5’4. But now they stood at eye level with each other.
“Oh my God…” she muttered, raising her hand up to the top of her head and sliding her flattened palm forward. Sure enough, she felt the top of his hair brush against her hand, when normally she should have run into his forehead. Denver didn’t even know what to say; he was speechless, wondering how it could’ve happened. “Did it…” Jackie began saying… “Did you… shrink… because of my fart?” There was an impossible stillness to the air, as they both absorbed what she had just said, slowly realizing it must’ve been true. But then as she felt a familiar feeling in her colon, Jackie realized she wanted to test it again.
Just as a smile formed on the edge of her lips, she shoved Denver back against the couch, pouncing on his lap as she felt the flatulence building, and crudely spun around while trying to shove his head downwards. He fought to get her off of him, but he was already a lot weaker from losing just a few inches. Not to mention that she was still dressed in just her underwear since she hadn’t gone to change since he came home, and there was a part of Denver that held himself back because he didn’t want to get too handsy with her. But that ended up being a mistake, as she again released another spew of gas, this time even closer than before, just as he managed to push her off. His nose crinkled in disgust as he leapt off the couch, but he’d already smelled it, and he shrunk down again in the middle of trying to escape, this time past the 5 foot mark.
He went for the door, but Jackie sprung from the floor and managed to tackle his leg, causing him to topple to the carpeted floor. He tried pushing himself back up, but Jackie’s weight was on his leg, and she promptly crawled over his body to make sure he couldn’t get away from her again. She might not’ve been a big girl, but he was the size of a 12 year old boy by now, and simply wasn’t strong enough to shift her weight off of him. She deftly turned him over before sitting on his upper chest. The previously 130-pound girl now felt like almost 200, so trying to squirm out from under her was a challenge Denver had never tried to do before. He tried pushing her off with his hands, but she just fought back, struggling to stay on top of him. She only had to keep him down until she had another fart ready to unleash, and she could already feel it building within her.
Feeling it only a few seconds away, she hopped forward with her legs outstretched, essentially trapping her older brother between her thighs, right below her crotch, and Denver started freaking out even more. Her panties were almost rubbing up against his chin, while he could feel the heat from her legs radiate onto his cheeks, while his sister looked down at him victoriously. “Jackie, please…” he begged, “If you wanna the shrinking, w-we should wait til Mom and Dad are back. What if it’s permanent?!”
She shrugged, crossing her arms above him. “If it’s permanent, then there’s no way you’d be able to go the rest of your entire life without smelling another fart of mine eventually. Hell, you wouldn’t even last it through the holidays with all the milk and cookies we’d be eating!” She laughed as she remembered how gassy milk made her, but Denver only paled as he realized nothing he could say would change her mind. “Oh! I think I feel it—“ She was cut off by her own ass, a fresh wave washing over the siblings. Denver could literally feel his neck heat up from the sudden expulsion, and this one was the loudest one yet too. She grinned down at him, but her smile began fading as he didn’t shrink this time. “Oh… What the hell?” she asked, clear disappointment in her voice. But then she realized Denver's mouth was open a bit more than normal, and her eyebrows furrowed as she reached down and clamped his jaw shut. The freaking out expression on her brother’s face told her all she needed to know. “Tsk tsk tsk, always trying to cheat,” she playfully scolded him, as his lungs began burning from not getting enough oxygen. He couldn’t hold on any longer though. Jackie could tell he was reaching his limit, and she let out a few more toots just as he finally opened up his lungs and desperately sucked in as much air as he could. She took her hand off his jaw and smirked as he began slowly dwindling down. His lungs felt replenished, but they replaced with a new kind of pain, the pain of an exponentially growing weight that covered more and more of his body. Her thighs grew taller and thicker on either side of him, her gleaming eyes rose higher, and she became so heavy he knew it would be physically impossible to even get her to budge anymore. Past four and a half feet, and then four feet, and even even down to three. He was the size of a child now.
“Having you just smell me by being kinda close doesn’t seem to be cutting it,” she sighed with a dainty smile on her face, slowly bringing her legs in, turning herself around, and straddling the entirety of his body between her tightly squeezing calves. Only his head was left uncovered. “I think you need to be right at the source.” Her bare feet tucked themselves under his head, giant toes wiggling excitedly against his hair as they lifted his head a bit off the ground. He could already sense what was about to happen, and the fact that she was wearing little more than a thong made him tremble with fear.
“Jackie, why are you doing this?! This is so weird, this isn’t like you!” He frantically squirmed all about, but there was no chance of escape. His sister didn’t even need to worry about keeping him pinned anymore; sitting still was doing more than enough.
“You’ve been pulling that fart-in-my-face shit for years, Denver,” she replied, frowning just at the memories of a hundred prior ‘pranks’ that weren’t as funny as he thought they were. “And every year, I keep wondering if maybe this’ll be the year you grow up and start acting normal, cuz that shit is sick, and it’s so fucking annoying.” She lifted her butt off of his body and raised it directly above his head, casting him in a shadow. He was nearly crying as he saw how big her ass already was—and it was only gonna be getting bigger. “So I think giving you a taste of your own medicine is the only way to get you to stop. Obviously I had no idea about my ability to shrink you, but,” she shrugged, “it goes pretty hand-in-hand with the punishment anyways, right?” And on that note, she dropped herself, and Denver screamed out for only a second before Jackie’s cheeks pounded on top of his head, wedging him right into the crack as she sat on his face. There were a few moments of silence, and then Denver's little sister erupted like she never had before. To him, the sound was almost deafening, an explosion that he felt all around him as her cheeks vibrated and a noxious burst of hot air blasted effortlessly through her panties and right into his face. He began shrinking immediately, quicker than ever before, coughing all the while. The three feet became two feet, and then by one foot in height he had pretty much his entire body cushioned within Jackie’s crack, trapped against the floor. And he was naked now too, having shrunk through the neck hole of his shirt, his clothes laying on the floor where his body had been moments before. Jackie’s farts were starting to sputter off, but the deed had already been done, and she couldn’t even feel him under her anymore. As Denver inhaled his last few gulps of his sister’s nauseating fumes, his shrinking slowed down. He didn’t even know how small he was anymore, but considering how much ass was surrounding him, it couldn’t be anywhere close to normal.
Jackie gradually lifted herself off of him and turned around. “Holy shit…” she muttered, legitimately surprised at how tiny he’d gotten with her third and final blast, sitting with her legs outstretched on either side of him again. Except this time, instead of his head straddled between her thighs, his entire body was. He looked to be half, maybe three quarters of an inch; way smaller than she’d even thought he might dwindle down to. A final tiny squeak sounded from her bum, but he didn’t shrivel any smaller, so she figured he must’ve reached the limit.
Denver choked as he saw how titanic his sister had become. Her legs were the size of giant airplane hangars, stretching hundreds of feet behind him. When he looked upwards, her face was so far away it looked as if he’d never shrunk at all, until she leaned down close to him and he realized it was at least 50 feet wide now. As shock set into his body from the realization of everything that had just happened, a grin formed on Jackie’s face. “I didn’t really think you’d get this small,” she told him, “but since you are, I’ll be able to make sure you learn to never fuck around with me ever again.”