Rachel of course!

Lily kept rubbing her much plumper behind. Her fingers running across the rump now stretching her old swimming panties. Digging into her skin painfully. She pulls down her panties to release the pressure, enjoying the enticing wobble that followed. Each run of her fingers across the soft skin sent electric tingles through her entire body. It was as if she was connected with her butt on a whole other level. It really was quite divine. Why had she not followed Rachel's advice earlier?! Oh well. She had to thank Rachel when she got home. But first...she could really do with a couple more reps to get the blood flowing. Maybe another orgasm or two couldn't hurt...

Rachel was holding a bag of groceries in one hand and a bag of new clothing in her other walking up the stairs towards her shared apartment. Her trip to the mall had been fairly successful. She had found a pair of running shoes that were half off that she was going to gift Lily on her upcoming birthday. She tries to fish up her keys from her pocket, balancing the groceries carefully up against the door. Putting some weight behind it. Right as she managed to pull up her keys she fell forwards with a surprised yelp...the door had opened by itself and the paper bag of groceries spills it's contents onto the hallway floor. A red apple rolls and bumps into Lily's foot. Rachel started replying as she got on all fours first, her gaze slowly wandering upwards until she interrupted herself. "Oh....hey Lily I didn't-...."

Lily had lost count of how many times she had cum. Each time connecting her a little more with her butt. Making it grow. Her thighs could probably kill someone at this point. Her behind so shapely it would make any woman jealous. It simply felt so good. The more she worked out the better it felt. It was as if her butt had a life of it's own and she loved every second of it. The only thought that could contain her excitement was the fact that Rachel was coming home soon. She rushed over to the window and looked out towards the parking lot. Perfect timing! Rachel was just outside. She rushed over to the hallway. Peeking out of the peephole in the door. Waiting patiently. It felt like forever. She wanted to show Rachel her new butt so badly! After getting a little anxious Rachel finally appeared in front of the door. Lily fumbled with the lock briefly, and opened the door excitedly. As Rachel fell she smirked slightly, she turned around and positioned herself above her face. Making sure her rump was in full view of her roommate. "Hey Rachel! Look! Bet you can't call me flat anymore!~"

Rachel bumped nose first into her roommates supple butt. Her nose indenting into the soft flesh. She almost loses herself in the softness from sheer shock. She leans backwards, sitting down on the floor. All thoughts of the spilled groceries exiting her mind. "What the fuck Rachel! Why are you naked! And why-....why is your butt so big?" Her eyes widened as if a lightbulb was turned on in Rachel's mind. She leaned forwards slightly, planting a hand on each cheek as she started massaging Lily's behind playfully. "And it's...so soft!" Lily giggled, swaying her hips gently back and forth to make her butt jiggle, moaning from her roommates gentle caress. "Mnnnn~ Do you like it? I bought this new leg press machine! You simply have to try it." Rachel's eyes shined, clearly already under the spell of this particular memetic event. "Yeah...I...if it means getting such a fat and juicy ass such as yours! It's just...perfect. Which girl wouldn't want a go?"

Lily smiled and didn't reply. Letting Rachel explore as much as she wanted. Her roommate took the opportunity and went a little crazy. Hands groping greedily as the fingers sink into Lily's flesh, almost disappearing completely into the folds. "Take your time Rach!" Rachel could feel her own excitement growing with each grope, getting slightly moist downstairs. Her breathing speeding up. It was nothing compared to Lily though who was getting really into the lovely massage. "Fffuckk...I could cum just from this alone....mnnrrr...." Lily moaned out, clearly pleased with the attention she was getting. However something clicked in her mind. She had to share this pleasure with Rachel properly. Sure it was nice to have her enhanced ass played with...but Rachel had to share her pleasure on another level. Lily pulled away to her own disappointment, but duties do come first after all. "Sorry Rachel...you can have a proper go later. Let me show you the machine first!" Lily turned around and helped pull Rachel up properly onto her two legs. Both of them still completely ignoring the spilled groceries on the floor as they walked into Lily's room.

Lily grinned incredibly wide as she gestured towards the leg press machine. "Tadaa! Neat huh?" If Rachel wasn't already so addled from whatever magic was bestowed upon this object she would have been quite unimpressed. The leg press machine really does look like any other. But Rachel was already under it's influence as she without hesitation took a seat on it. Rubbing her hands along it's cool metal chassis. "Oh wow...I see what you mean! Where did you even get this? Don't tell me at the second hand store..." Lily snickered, nodding in confirmation. "Yeah! And Beth let me have it purely off my points. They were gonna throw it away otherwise. What a shame that would have been. Right?"

Rachel nodded as she looked at Lily. Her legs spurning against the weights. She started pushing it back, beginning to do some reps without much thought. Still chatting to Lily. "Yeah it would have been a real shame...I feel like I owe you an apology. Not because I called you flat mind you, but because I thought you were such a dork heading there early all the time...but I mean look at this steal! A leg press machine that gives you a fat ass is...mnnff...to die for...." Rachel panted, already feeling the strain from the machine. Lily must have upped the weights significantly over the last couple of hours of training her butt. Rachel's loins burned with the same pleasurable tingle that had claimed her roommate. It didn't take long before Rachel felt herself connecting with her butt. The nerves extending outwards into the rest of her body like tendrils. Sending wave after wave of pleasure. Each rep causing a ripple of added flesh to jiggle enticingly. Rachel huffed and puffed, grunting as she gave it her all. Since the girl already was so well trained her upper limit seemed much higher compared to lily's first try. It took her several minutes of burning pleasure before she reached an apex. Cumming powerfully with a long drawn out sigh of utter relief. She panted heavily as she creamed herself. Not seeming to mind this degrading act at all. A wide pleasured smile spreading across her face as a calm came over her. Rachel relaxed her legs and then stood up from the machine. Pulling down her now strained jeans and torn panties. Revealing a huge bubble butt that rivaled Lily's. Rachel rubbed her newly enhanced rear and gave each cheek a playful slap. "Mnnnn~ Thanks Lily...that was great. I see what you mean now. We should share this with all of our friends!"