Expansion Of Mass

In this story, Lynn and Issac are provided a new invention to "test" by Issac's roommate, both are eager to see what's in store for them!

Be sure to check the Tags and I hope you enjoy the story!

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Issac was admittedly a bit nervous as he knocked on Lynn's door. Not because of whose door it was, but because of the strange device nestled safely in the nondescript brown paper bag he carried it in.

It had been two weeks since he had "borrowed" another of his roommate's devices after hearing his roommate dropping hints as to what it could accomplish. After a wild night with his girlfriend he'd had to return the collar to his roommate. He'd spent the next hour detailing his own experience with it. In hindsight it had been obvious but his roommate had basically wanted Issac to take the device, preying on his big breast fetish in order to gain a couple new test subjects discreetly.

He had promised to provide updated and further devices to him for testing and much to Issac's surprise when his roommate handed him the bag while giving him a barebones explanation, saying nothing of how the device was to be used aside from that unlike the collar they had used last time this device should allow for more "targeted" growth.

Not that Issac hadn't been busy these last couple of weeks, in addition to his studies he'd spent several nights with Lynn, the passion and intensity they'd experienced when using the collar had really ended up pushing them to a new level of their relationship. In addition to more sex they'd opened up to each other on a much deeper level than before. Lynn talked about what had led her to be displeased with her tall and thin frame and Issac had been more open about his fetishes, both the more mundane and the wilder ones.

Issac had been worried she might mistake his love for big breasts as though to say he didn't actually desire her at all but fortunately she took him at his word. Of course, the way his roommate had explained this new device had him worried he might let his fetishes get the best of him tonight.

Issac's train of thought was interrupted as his phoned dinged at him, pulling it out of his pocket he saw that Lynn had sent him a text;

[Door's unlocked, just getting comfortable...]

Issac slid the phone back into his pocket before opening the door and letting himself in, being sure to lock it behind him. Lynn wasn't anywhere to be seen, given how small her place was there was basically only one place she could be. Walking towards her bedroom he was greeted by quite the sight as Lynn, naked as the day she was born, lay across her bed.

"My, isn't

someone

eager?" Issac joked as he set down the bag on her dresser and pulled his shirt off.

"You can't blame me, I've been looking forward to trying another device, and telling me we can choose what to grow this time?" Lynn explained as she sat up, even sitting on the bed she was almost eye-to-eye with him, didn't help he was almost a full foot shorter than her.

"

Maybe.

" Issac cautioned, "My roommate didn't give me much of an explanation, I think he's treating us as guinea pigs for real this time." Issac explained as he undid his belt before dropping his pants to the floor. As Lynn got up Issac noticed a muffled crinkling noise coming from her bed.

"Oh, yeah. It's like a protective sheet for the mattress just in case you cum like a firehouse again." Lynn explained before hugging him from behind, her height made it easy for her to lay her chin against the top of his head. He could feel her heart racing in excitement through her chest.

"Well go on, let's see it!" Lynn demanded excitedly, watching as he reached for the bag and gently slid its contents out on top of her dresser. He hadn't looked yet and was a bit surprised by what he saw. It almost looked a bit like a taser, complete with pistol grip and two metal prongs at the front that didn't really look like they belonged. From the back of it a long cord ending in a wall plug stuck out.

"Huh, the collar didn't need to be plugged in..." Lynn mused from above him. Issac swallowed nervously, not all that confident in the device's housing looking like a taser.

"Uh yeah, I think I remember my roommate saying something about not being able to create something out of nothing?" Issac gingerly picked up the device before continuing, "The collar was really just redistributing what was already there." he explained as he turned over the device in his hand.

"I mean, I guess that makes sense...somehow." Lynn mumbled as she watched him examine the device. Reaching around him, her hands made their way towards the prongs fiddling with them a bit before she pulled on them, extending each one to about a foot long, though the tips were capped in a brass colored metal. The prongs were mounted on basic swivel joints, giving them a surprising range of motion. Ideas were already forming in Issac's head as Lynn fiddled with the prongs for a bit more before moving out from behind him and grabbing the plug to the device off the floor.

"Let's plug it in and try it!" Lynn called out eagerly and she stepped over to the wall, bending over in a way to show off ass in the most pandering way possible, Issac's thought derailed momentarily.

"Well?" Lynn questioned him, pulling him back to the moment.

"Uhh I guess, it still feels like it might be...dangerous?" Issac cautioned. Keeping his finger off the device's trigger as he continued to inspect the device. Unlike the collar they had used before this one didn't have any dials on it, nothing but the trigger and the prongs really. Lynn sighed quietly as she walked over and sat down on the edge of the bed.

"Why would it be any more dangerous than the collar was?" Lynn pointed out, "You were just fine using that on me." She had a point, and it wasn't like his roommate was actually going to do anything maliciously to them. Issac stared down at the device as if simply looking at it would somehow unlock its secrets. After a moment of silence Lynn spoke up as she reached for the prongs.

"Here." Lynn adjusted the prongs so that they were only about an inch apart. "Now try it." She instructed. Issac looking down at the device, making sure the prongs were pointed away from both of them, he tensed up slightly as he gently pulled the trigger.

Expecting some dangerous looking arc of electricity Issac was comforted that seemingly...nothing happened. Both waited with anticipation to see if anything would happen until they both heard a dull humming emanated from the device. Clearly the same sort of hum the collar had made.

"Okay that's promising..." Lynn mused as she reached out, prompting Issac to pass the device to her. As soon as he released the trigger hum faded away and he passed the device to Lynn. She looked it over briefly before adjusting the prongs and pressing the device against the top of her breasts and pulling the trigger.

"Oh...yeah it's...

aaahh

...working all right..." a sensual moan interrupting her. Issac's gaze was immediately drawn to Lynn's chests. Clearly this device had far more potential than the collar, as he could already tell that Lynn's chest had filled out. Lynn clearly noticed as well, promptly releasing the trigger, breathing heavily as she pulled the prongs off her chest.

"So it felt the same as with the collar?" Issac asked, excitement tinting his tone as he watched Lynn feel up her chest, wincing slightly as she lightly pinched a nipple.

"Oh yeah, but better, or rather faster?" Lynn remarked as she finished examining herself and crawled onto the bed, the device still in hand. "Ready to start for real?" She teased.

Issac's cock jerked at the invitation, already well on his way to an erection thanks to Lynn's teasing. He did want to get right to it...but given he went behind Lynn's back with the collar and changed a setting without telling her he wanted to make sure that he didn't let himself do anything like that again.

"H-hold on...maybe we should set some...ground rules?" Issac stammered out, a mix of shame, guilt and embarrassment crowding his brain. Lynn cocked an eyebrow but otherwise remained silent. Issac took a deep breath before continuing.

"Well uh...how about we take turns growing something on the other person, whatever they want." Issac laid out, Lynn listened intently.

"Mmm I do like the sounds of that, how about 3 turns each before we focus on

enjoying

the growth?" Lynn added, clearly ready to see where the night would lead. If this device worked even better than the collar Issac wasn't sure if he would last three rounds of watching Lynn grow on top of himself growing but to be honest that wasn't really the sort of 'ground rule' he was worried about.

"And uh...no immobilising the other person, last time we didn't really get much of a choice in what would happen, but we should probably keep ourselves from getting carried away." Issac added, more meekly than he wanted, for a split second Lynn looked like she was going to say something but simply nodded.

"Sounds good, You can't fuck me properly if you can't move after all..." Lynn agreed before patting the bed in front of her and giving him a look that made his cock twitch, now hard enough to tent his pants out enough that you couldn't miss it. Taking a breath he started stripping down as Lynn watched eagerly. Had Issac been less distracted by Lynn's naked form, the prospect of using the device and general arousal, he might have noticed how...hungrily Lynn was as she watched him, almost like a predator gazing at its next meal.

Instead Issac focused on stripping down quickly and joining Lynn on the bed, his hard cock bouncing around as he got on the bed, "standing" on his knees at Lynn's direction as she adjusted the prongs on the device.

"Seeing as I got changed first with the collar last time, it seems only fair that you change first this time." Lynn proposed, now ready with the device but waiting for Issac to accept the role of initial guinea pig. He nodded, he pretty much knew what Lynn was going to grow on him, his dick and balls, what remained to be seen is what she'd do for the 3rd part of his anatomy.

A shiver shot up his spine as he felt the prongs press against his balls. He was a bit surprised she was going for them first, but she had admitted that watching him cum excessively last time had sparked a new fetish for her. He tensed up a bit as Lynn pulled the trigger. Unlike with the collar the hum and the accompanying tingle started right away, Issac grunted as it enveloped his balls but didn't spread to his whole body like with the collar. Instead it grew in intensity rapidly leaving him gasping as he felt his balls start to grow almost immediately.

"W-wow...you were right about it being...faster..." Issac wheezed, reaching out to Lynn's shoulder to steady himself as his hips shuddered. His cock throbbed in sympathy, a drop of precum already forming at the tip. Lynn's free hand made its way to his thigh, gently caressing it but also 'accidentally' brushing up against his growing balls, causing them to sway back and forth, making their growing weight even more evident as time wore on.

"Mmmm looks like having these big heavy balls feels real good huh..." Lynn teased as Issac's hips squirmed, each time she 'accidentally' grazed his balls with her hand it sent jolts of pleasure up his spine, precum now leaking from his cock and running down the underside of his cock before tickling his increasingly sensitive balls until finally dripping down onto the bed.

Issac felt an orgasm building up, just from the growth and Lynn's teasing. But beyond that, he feels something else, it isn't just that his balls are growing bigger, as the weight increases and they pull down on his hips more and more, he knows they're not just growing bigger, but growing

fuller

too. As the prospect of cumming grew larger in his mind he realized it wasn't just that he wanted to cum, no, it was very quickly becoming a

need

to cum. His balls weren't just large, they were quickly getting full and he'd have to release that growing pressure sooner rather than later.

"L-lynn...I'm gonna c-cum if you k-keep going..." Issact stuttered before glancing downwards and groaning as his balls happened to swing forward, revealing their true size, already beyond the size they'd grown last time, a testament to the efficiency of the new device compared to the collar.

"Mmmm I bet, they look so full..." Lynn practically goaded him as she kept the trigger pulled on the device, forcing more and more cum into his swelling balls. His breathing grew more laboured as the expansion continued and his balls grew enough to press against his legs, no longer a little wrinkled sacks they were starting to grow tight, as the accumulation of cum outpaced the growth of his testicles.

"Lynn..." Issac forced out of gritted teeth, on the verge of being overwhelmed Lynn finally relented and released the trigger.

"Mmm I supposed this will do for tonight." Lynn commented as Issac slumped back and he caught his breath, spreading his knees out as he settled to give his balls space. They looked comical beside his unchanged dick, precum still oozed out as he sat there having been brought so close to cumming.

He had been so focused on his state he hadn't noticed Lynn as she sat down behind him, pressing herself against his back, he could feel her little rock hard nipples gently poking him as a bad feeling washed over him just as she slid her hands down his thighs, coming to rest near his knees.

"You need to cum, don't you, I mean how could you not, they're so big and full..." Lynn whispered in her ear, her closeness sending a shiver down his spine.

"But if I cum right away..." Issac tried to reason with her, but he knew she had him right where she wanted him as her left hand slowly slid up his thigh before shifting over to his sac, gently pressing inwards and forcing a moan from his lips.

"You didn't really think you'd get away with only cumming for me once tonight, did you?" Lynn asked, it almost sounded like a threat but Issac realized she meant it as her other hand wrapped around his cock and started slowly jacking him off. Fortunately his dick wasn't more sensitive yet, but he had already been so close, it wasn't going to take much for him to cum.

He tried to resist, to hold it back, normally it probably would have worked but he was already so close, and with the way Lynn was caressing his balls was too much, she had barely been jacking him off for twenty seconds before he came. His hips bucked, somewhat restrained by her weight on top of him, as his balls churned and contracted in pulses before finally cum blasted from his cock. The pressure fell immense and yet he stopped cumming much sooner than he expected. By far still an impressive amount and the fullness of his balls felt just as intense as before.

"Mmm see? Didn't that feel

good?

" Lynn whispered into his ear as she pulled her hands away from him, actually giving him a chance to recover. She helped him lay back, the position letting his balls rest on the bed instead of tugging at his crotch constantly. Although the need for release hand't really diminished it wasn't quite as "loud" as it had been before with Lynn egging him on and he managed to catch his breath before looking up at Lynn as she sat down beside him.

"I thought we agreed on nothing big enough to immobilize..." Issac sparked up to Lynn who looked away.

"I don't know what you're talking about, I'm sure you can still move around..." Lynn responded in a somewhat mocking tone before her voice turned a bit more sincere, "If not...well I can always help drain you some more..."

Issac's cock spasmed lightly at the thought, as much as he was worried about being done for the night it was clear both Lynn and his body had other ideas.

"Careful, I'll hold you to that." Issac teased as he eased himself up onto his elbows as he gazed at Lynn, his heart rate still not quite back to resting levels knowing more was to come.

"Mhmm I hope so, but for now, I'm really curious to see what part of me you'll grow first..." Lynn quipped, as she stuck her chest out with the clear intention to influence him.

Lynn's teasing aside, what did he want to grow first? Lynn's chest was obvious given she knew his interests in more detail than he'd ever shared with anyone else before. And yet...was there something more fun he could start with? He knew he'd had to grow her pussy at some point, no way she'd not grow his cock to match his balls. His lips turned into a smirk as he recalled how her pert little nipples pressed into his back while she was jerking him off. It'd be a little difficult to do, but well worth the effort.

"Here, help me up." He asked, holding out a hand, using Lynn for support as he got his legs back under him before getting her to sit down in front of him as he grabbed the device and began adjusting the prongs for what he had in mind.

Lynn meanwhile was practically vibrating in excitement. Although she used to feel pretty self conscious about her lack of curves combined with her height he'd helped bring her around before the collar, letter her see and experience the unique aspects of her body with someone short like him. After the collar he was a bit worried she would hyperfixate on wanting or somehow regaining all the curves it had given her but it was sort of the opposite. She gotten what she wanted and she had enjoyed herself yet it also showed her that outside of the bedroom it wasn't all it was cracked up to be, her balance was off, she kept bumping into things and not being able to reach the cupboards had been annoying enough that she'd used the collar to get her height back even before they called it for the night.

She was excited to have fun but didn't come to desire the curves for their own sake. Frankly Issac was a bit jealous, he still felt a pretty strong desire to grow his cock in particular, though Lynn had shown him it wasn't needed to please her there was still a little corner of his mind that nagged him that it'd still be

even better

if he were bigger. Shaking his head a bit he focused on the situation at hand, the prongs were ready. All he had to do was try to get Lynn to sit still long enough, something that was sure to be difficult as the device worked but he had to try.

"Alright, try not to move now..." Issac cautioned Lynn as he moved the device towards her chest. At first she smirked, imagining she had him all figured out but she gasped as the cold prongs pressed directly against her nipples. Before she could say anything else he pulled down the trigger and the device began to hum as Lynn let out a moan.

Lynn arched her back as her nipples started to grow both in size and sensitivity. Issac did his best to keep the prongs on her nipples but there was sure to be some collateral growth applied to her breasts. Still Issac did his best and was already being rewarded, Lynn's small and stiff 'tic-tacs' were already visibly bigger and her areola slowly spreading across her chest.

"Fuck it's so much more intense..." Lynn cooed as the growth continued. It made sense, whether by design or by chance the growth that came with the collar and this new device was always accompanied by heightened sensitivity. The device being far more localized than the collar seemed to increase the effect, although Issac's balls had already been swollen they simply weren't that sensitive to begin with, Lynn's nipples on the other hand were a different story. They'd always been more sensitive, perhaps a sort of tradeoff for being so flat and thin, and if the device was boosting that Lynn was feeling it for sure.

As the device hummed away and Lynn moaned, she moved her hands suddenly and for a split second Issac was worried she needed him to stop but he watched as her hand slid down to her own crotch, her fingers wetly playing with her soaked pussy. She threw her head back as she doubled up on the stimulation, Issac had to shift the device around to try and keep it on target.