Motion Activated [Early Access] (Patreon)

You couldn't believe your eyes, staring slackjawed as the pert little booty swelled under her waiting hand. It was quick, but there was no mistaking the 5 lbs of extra booty stretching her panties.

"See, I told you! The serum makes it so whenever the affected tissue is 'agitated', it grows!" 

Mistaking your stunned silence for misunderstanding, she gave herself another slap. And again, as the new flesh reverberated it briefly swelled like two waterballoons. The quaking mass even jiggled down her thighs, which also looked slightly larger.

Dry mouthed, you could only think to ask "D-do you have to slap it to work or.."

"No, weren't you listening? The key is agitation, like in a mechanical sense- look." 

To demonstrate, she started shaking her hips. About 10 lbs ago, there wasn't enough butt mass to move; but now.. Now her two spheres jiggled and smacked erratically, reverberating against eachother and their own increasing volume. Her poor panties were being forced up her sides to rest on her comically small waist as more mass swelled under them with each movement. 

Suddenly aware of the magnitude of her growing backside, you were deeply concerned. How would she go outside with a butt like that? Do they even sell clothes big enough to cage those two basket-balls of backside? What if she runs up stairs too fast.. or at any speed- really.. 

Again, you notice- in the mere moments the once basket-ball sized mass was surpassing beach-ball sized proportions. She was visibly too captivated in the sensation to be paying any mind, in a rush you charged forward to still the huge mass. You're barely able to wrap your arms around her new diameter, but its just enough to quiet the waves of soft flesh- just as it slowly finishes swelling beyond your grasp.

Startled from her reverie, she says, "See! I'm glad we're on the same page, that's what I was thinking.. " as she bends over, pushing her two bean-bags of mass against you...