Outsized By Your Sister [P]Written & Edited By AmnoartistChapter 1: Bets PlacedA few days back I polled by Patreon supporters on which "Part 1" should be posted on here next, and the winner was Outsized By Your Sister. This series is arguably different from most of my other stuff because it's a second-person perspective story and it (clearly) focuses on the relationship between siblings - "you" and Katie. There are another four parts available to my patrons, if you're interesting in the continuing tale. Hope you enjoy Every so often, there comes a time when placing a bet is more a bad idea than good, for instance, when someone bets their last dollar on something, or maybe even their car. It’s never good when that happens. You found that to be the case when you bet with your younger sister, Katie.
It all started when you got into an argument with her over which gender was the strongest…
“Nu-uh, females are the stronger gender, their bodies are specifically built to withstand great pains like pregnancy.” Katie was livid at the prospect that males were stronger – the same view you repeatedly stuck by whilst flaunting your outrageously built physique, as if that alone was enough to prove the point. “They also mature faster,” she added.
Even if that were the case, you weren’t having any of it and did whatever you could to block out the droning on Katie imparted; you reached down and pulled up a dumbbell from the pyramid rack – a 70-pounder – and started curling, offering a somewhat heartless grin at Katie through the mirror. You weren’t always a total asshole – just when Katie brought up the suggestion that females were stronger than males, which just never could be true.
That was then. Now things are much different – hilariously so. But before we get into that…
“Fine. How about we bet on it?” Katie knew you to be quite the betting man when money wasn’t tight, so right now she had your interest piqued. Watching you turn to her with a curved brow, the petite blonde smiled. “Let’s see if I can…um…make my arms grow fifteen inches within a week.”
“A week?” You knew it was physically impossible for anyone to make their arms grow fifteen inches within that space of time. At least without hormones being ladled into them like soup. It was almost cute that Katie thought she could actually pull it off.
“Yeah, a week.” Katie was serious about it too; her face had been scrunched up into a stern pout – a unique characteristic from the girl that made it known she wasn’t kidding.
You couldn’t stop yourself from bursting out into a fit of laughter at Katie’s suggestion, knowing she couldn’t grow one inch larger within the space of a single week, let alone fifteen. But you’d at least humour her – it would be a nice way to teach a lesson. “Okay, one week. No backing out, you hear?” Your voice held an air of derision that Katie noticed, but didn’t react to. Doing that meant the bet was lost before she even had a chance to start.
Katie smiled smugly. She had no intention to back down, eager to put you in your place.
///
The Next Day… Katie’s eagerness to prove her point stirred a secret, relatively unknown fire within, as she woke up the next day far earlier than usual; she yawned at dawn’s rise, the sun bursting through her window as if to personally rouse her from her otherwise splendid slumber. You were still asleep in your room and would not, in all likelihood, wake until midday.
Already a step ahead by being changed into her workout gear, Kate would normally have a bowlful of chocolate flakes for her breakfast alongside a glass of milk. But she set a goal to change her diet up in her favour to help win the bet, surmising every little helped. So, learning from your own dietary regimen, she cracked open a few eggs and made egg whites with toast. It was delicious, to say the least, but somehow she felt hungrier than usual; her stomach growled loudly, aching her insides slightly with her increase in appetite. Acting upon that, she went against her otherwise better judgement and used the remaining eggs to make more egg whites and toast, essentially leaving none for you when you’d eventually wake.
“It’s not like the eggs are exclusive to him or anything,” she said, before ravenously chugging the last forkful of egg white down her throat, now satiated until her next meal came later in the day. Katie found the gorging on food had resulted in a food baby that she found to be quite humorous; giggling, she stroked her gut tenderly for a moment, listening to the food gurgle before setting off to the basement gym. Her rookie’s mistake was working out on a full stomach – but little did the chirpy blonde know that by the time she’d reached the gym her stomach was flat again, as if no food had been in it at all!
///
Katie was nervous around the gym for once. Sure, she’d always seen and heard you work out daily, but it was a completely different feeling when she was the one doing the curls, squats and flyes. But her anxiety wasn’t crippling enough for her to back down on the bet she came up with.
“Alright, let’s see what we got here.” Katie scanned the different machines carefully, picking out the needle of a machine in the haystack of gym equipment, not entirely sure what was best to use. She knew to use something that would help make her arms grow fifteen inches to win the bet, but had no rightful clue what machine did what. “Hmm….”
Eventually, thankfully to be on the safe side of things, she stuck with the dumbbells you used yesterday. Carefully she picked a pair up, judging the weight in the hand. You had told Katie once in the past to stick with a weight that felt right in her hand, though it didn’t mean much to Katie at the time. If only she did – what would she have looked like now if that were the case?
A pair of 30-pounders felt just right in Katie’s hand. Wasting no time – and forever eager to win that bet – she slowly, carefully manipulated the weight in her grip, watching her form in the posing mirror, making sure there she stood upright and her arms were ever level where they should be. It was boring for her to stay so still, being the lively one of the siblings, but Katie pressed on, as did other things; little did she know – like with the food baby – her arm was swelling with growth and power each time she brought the dumbbells up. Her innocence to the motion made Katie believe it was just a pump she was experiencing, but she would soon learn thar that was not the case.
“On my ninth rep already!”
Katie glanced down at her bulging arm with a brisk smirk, pleased with the ‘pump’ she was receiving. It was when she saw the veins suddenly bulge and pop to the surface of her skin that she realised the bizarre yet advantageous truth: she was actually growing ever so slightly with every rep.
It was strange – not to mention scary – to look at, at first, but the apparent rapid increase in size proved exciting to Katie; dropping the dumbbells carelessly, she pulled her arms up into a flex, watching the ball-sized limb rise to an impressive, vein-crusted peak, thrumming with the slightest ripple of growth, adorned with deeply defined cuts and grooves. And those were just her arms!
Glancing behind her, Katie turned her attention to the leg press with a smile as the blossoming of an idea came into existence. Her now larger arms hung at her sides, the growing blonde shrugged her way towards the machine and squarely sat on it, setting the weight to around 2000 pounds – a little over your current max!
The first press was both heard and felt; the sounds of a wet sponge being drawn out and shorts slowly tearing echoed across the gym as Katie winced in sync with her determined rep, calves visibly quaking and twitching in the impending build-up to grow in size and power. As they grew, so too did her quads; ballooning outwards in a violent fight to be contained within the blonde’s shorts, but to no avail, eventually tearing under the seat to expose her hardening glutes. It seemed every part of her grew, whether it was being worked out or not; quads, calves, glutes, arms, shoulders, abs, even her neck widened from just moving this way and that with her eyes that watched the growing occur.
“Oh fuuuckkkk!” It was orgasmic. If Katie pushed herself hard enough, it wouldn’t be wrong of her to think she could outsize you within the next few minutes, let alone by the week’s end. And so, she did, adding not just more weight, but double it. Could this stand to reason that her growth would occur twice as fast?
Be that as it may, she pressed again, this time almost screaming with pain as the growth she sought was almost instant. Muscle fibres split themselves apart and rebuilt stronger in the blink of an eye, skin tissue visibly throbbing as it struggled to make space for the outrageously sized girl who pressed yet again, playing deaf and dumb to her gurgling stomach that sought food once more, abs pushing violently against its layer of skin, her panties on the verge of being sodden with love juice.
With a thunderous clatter the leg press collapsed under Katie’s behemoth weight, rendering it useless. Even so, her muscles seemed to continue their expansion, if even for just a moment; her calves rubbed together in their fight against one another for growing space, grinding this and that way, pulling and pushing until, in sync with Katie’s climax.
Eventually the growth stopped. Her bare legs dripped juice for what felt like a full minute before she found enough composure to bring herself back to reality. Grinning sadistically, Katie turned to her side as she flexed her calf in the posing mirror. The muscle in question must’ve been at best 33 inches thick and covered with layer upon layer of veins, each thicker than the other. Katie knew right there and then without looking that she was bigger than you. There was no questioning it – that much was certain.
“I can’t wait to see his face when he sees these,” she said in a cheery tone, bringing her arms up into a proud, shadow-casting flex, curious how large they were.
///
Later… “43 inches. Your arms are…43 inches.” Your mind almost went numb at having to read out such an absurd number like it was an everyday thing. You pulled the measuring tape away, still coming to terms with how Katie got so huge in a matter of what had to be minutes. It was humanly impossible, at least without drugs, and you could tell she hadn’t used any; there was no horrifying outbreak of acne, no male pattern baldness or any negative effect associated with hormone use. And yet, there she stood - thrice your width.
“You know, when Mum finds out about this, she’ll flip.”
Katie didn’t really care for what her Mum would say, at that moment, “What about my thighs here.” She knew she had you under her thumb at the moment, and couldn’t resist being smug about it, if even for just a little while. That would teach you to think twice about which gender was stronger. She flexed her right quad out in front of you and watched the gaping massiveness undergo the slightest dose of growth; the same wet sponge sound was heard. “I’m reckoning they’re about 50 inches, give or take the growth there.”
50 inches? That just had to be a crazy number to think about, surely? You weren’t so ecstatic to find out if it was the truth, either. “I’m thinking less, like 43 again.”
Katie smirked. “Want to put a bet on it?”