Jen was caught off-guard by the sudden impromptu massage you were giving her, shuddering from pleasure as she wasn't used to the feeling. Your diminutive hands were skillfully pressing and kneading her flesh in ways she hadn't even thought about though she remembered how you had massages Lillian's belly to calm it down somewhat from her hunger. She was very pleasantly surprised because she wasn't sure you'd be as receptive to her flirty advances as she had first hoped and decided not to say anything, a little afraid to scare you off from whatever you were thinking of doing.
Focusing on the massage partially took your mind off the embarrassment, enough that your brain didn't melt from feeling Jen's warm although there was some noticeable tingling on the inside of your palms and arms. So far, no negative reaction on her part so you hoped that was good enough, slowly moving to massage more of the jiggling globular surface though as Jen was sitting, you wouldn't be able to do the whole cheek without the risk of falling and rolling off.
Moments later you snapped yourself out of your thoughts and decided not to linger too long on the massaging part because that could also give Jen the wrong idea so you went back to the middle, where the cheek's curvature had its apex and got on all fours, kissing it like you did the first time. Your whole body shuddered because feeling her soft skin on your lips gave you mad tingles all over.
Jen couldn't help but shudder a little herself when your lips made contact. She felt that way more strongly than your little massage or when you were just resting on her butt. She also felt goosebumps forming in response to her excitement and bit her bottom lip, barely keeping from making any noises though both Cindy and Zuemy noted that going by how much she blushed, Jen really enjoyed that.
"Well done! But you're still missing the other one" Jim said with a cheeky grin but you gave him a deadpan stare "Hey, Jen was the one who said both!" He added, knowing you couldn't get mad at her.
Cindy simply smiled and gave you a thumbs up and you decided to better get on with it, walking towards the middle of her butt, staying careful to avoid tumbling down and having to climb from the beginning all over again and as its curvature became more pronounced the more you advanced you had to grab onto it with both hands. Jen giggled softly, tickled by your tiny footsteps as well as your inadvertent fondling of her asscheek. A few minutes later you found yourself before her crack, which had mostly swallowed her red thong by now with the main proof of the garment's existence being the cloth triangle above the dark chasm that voraciously had swallowed the rest.
Jumping from the side was far from your forte and you weren't confident at all that you could make the jump. If Jen were laying on her stomach then you'd be able to run and gain enough impulse to leap across. You sighed and shook your head, you remembered that Jen's not supposed to aid you while the dare was ongoing but what were you going to do? You could climb down to her crack and then climb up on the other side but you didn't think that'd fly with Jen, besides even your parents had told you that you should only climb into places on other people's bodies if asked to or given consent.
"I don't think I can make it to the other side" You said, looking at Jen first and then at Jim.
"Then just climb down and climb up on the other side?" Zuemy replied.
"Come on, that might be a bit much" Cindy interjected.
"I wish I could help you but I can't" Jen said in a soft, apologetic tone.
"I mean, I only said no fancy hand-elevators... you could help him as long as you don't use your hands" Jim spoke, giving Jen a wink which made her smile.
"Oh... okay but how?" Jen wondered out loud.
"If you stand up and sway your hips your cheeks would clap. All Blaise has to do is get the correct timing and jump over to the other side" Cindy said, sounding like she knew way too much on this specific topic. You blushed intensely but Jen smiled and nodded.
"That's an awesome idea, thank you!" Jen then asked you to hold on before she stood up as slowly as she could and felt that Lillian glared at her for a moment for this too had been something she largely learned from her.
[Flashback]
"What do you mean 'how do I get a big butt?', yours is pretty big already" Lillian said with a raised eyebrow after Jen asked her that question.
"I mean it's not huge like mine but yours is still one of the biggest, like easily top 5 or top 10 in our school"
"Yeah but I want it to be bigger still" Jen laughed a little "I've tried to up the calories but these keep hogging most of it" She giggled, cupping her large chest.
"Oh, what a tragedy" Lillian rolled her eyes "You know that yours are like the biggest boobs in the entire school not counting Dolores' and some other extra large ladies? You've got even Lulu or the Principal beat! But you wanna go for the Booty League instead"
"Y-Yeah. I mean, I like my butt better and I'd like it to get some of the spotlight instead of it being my chest all the damn time" Jen replied.
"But it's not just getting it bigger, it's also how you move it... it also depends, do you wanna muscle it up or fatten it up?" Lillian asked, giving a cheeky grin towards the end of her question because she was practically sure of Jen's answer.
"What do you think?" Jen chuckled, raising an eyebrow herself "Hey, I do know some moves, you know I go to Mexico for vacation every year? I've picked up a thing or two"
"Good spirit! As for the other question, welp... in that case I'll teach you the dieting my mom taught me, got these buns all bouncy and jiggly as they are today" Lillian giggled and that day marked the beginning of their efforts to make Jen's butt grow larger.
[End of flashback]
'Can't blame anyone other than myself for that one I guess' Lillian thought. Trying to see the bright side, at least it was more or less clear that you weren't too afraid of big butts like hers and might even be into it. Something kept telling her that she should know this for sure but it made no sense, like some distant memory that remained disconnected and blurry.
"Alright, hold on tight and be careful!" Jen said just as she began to sway her hips, taking her time to increase the speed into proper hip-shaking. Even with the relatively tight jeans she wore, her admittedly big booty still bounced quite a bit and jiggled in a way that'd be hypnotic to any red-blooded guy watching though Jim politely chose not to look, something Cindy noted.
Meanwhile, you did as Jen said and held on tightly, feeling as if the entire world was shaking since, well, the mountain-sized asscheek you were clinging on was swaying from side to side, jiggling more than you expected, making it almost feel like you were trying to grab onto pudding. Once again, it was most likely a good thing this was far from the first time you deal with something like this as muscle memory kicked in and your grip remained constant.
Soon, you heard the first booming clap as Jen's cheeks bounced into one another and the impact brought even more bouncing and jiggling, causing some waves of soft, doughy flesh to traverse the round, meaty expanse but you rode these fleshy waves without much issue. You looked again at Cindy who smiled and gave you a thumbs up once more, the look in her eyes made it seem like she was convinced you were fully enjoying this and at least in a way she was right, you were a bit concerned about getting flung off but staying on Jen's cheek while she did these incredibly sensual moves was priceless. It took another booming clap to wake you back to the world of the living and you remembered that you still had a task to accomplish.
'Looks like Lillian's been teaching well' Zuemy thought, nothing that Jen was definitely using her larger friend's moves. Plus, she was aware that Jen had been following Lillian's dietary advice which, coupled with Dolores' generosity with their food had made it grow even larger and jigglier. She even remembered hearing Jen say she had gained 2 inches a few months ago.
As for you, it was hard not to get distracted by the immense show Jen was putting on and you could even feel that your lower anatomy was lightly poking into her flesh, hoping that she didn't notice. You were getting too enraptured by her massive booty and its sexy swinging motions but you needed to actually pay attention to the timing so you could leap to her other cheek and that required the next thing after an iron will.
Taking a deep breath, it took every bit of concentration you had not to lose yourself into the happy daydreaming that looking at such an incredible display would normally cause. You watched her cheek bounce into its opposite a few times to gauge the time and then you waited for the next one, jumping with all your might right as the meaty globes met and even bouncing off Jen's cheek a little, which she definitely felt.
It turns out you underestimated your own strength because not only you made it to the other side, you slammed into it face-first, sinking considerably into her squishy flesh but you managed to hold on before bouncing off. Unheard by you, Jen gasped quietly because it felt like you were hugging her other cheek and even burying yourself into it. She was delighted to know that she had enough back there for you to sink into.
You waited a few moments for the rest of the jiggling motions to subside and then you climbed up a little to repeat the process, you diligently massaged Jen's cheek as much as you could without risking falling and once you were done you headed back to the very middle of it, getting on your knees and then on all fours before planting a kiss on the "ground".
"He did it!" Cindy was the first to cheer for you, Jen was too flustered to actually speak and waited for her own face to cool down, after which she gently picked you up and pulled her pants back up before taking a seat on the floor and putting you next to her. She then spun the bottle on your behalf...