"So… how should we start?" Rarity asked, confused.

"First… contact with the flesh of the glutes." Twilight declared as she put on a rubber glove and let it snap.

"C-Contact?" Rarity echoed, surprised.

"Yes, in order to create a baseline. It shouldn't take long." Twilight assured her.

Rarity swallowed nervously as she heard the other rubber glove snap onto Twilight's hand. She was starting to have second thoughts about agreeing to this. However, it was too late now.

"This may sound a bit awkward, but you're going to have to remove your undergarments for this test." Twilight told her friend, grinning sheepishly.

"Oh, of course." Rarity replied, reaching under her skirt and pulling down her lacey white panties, all the way down to her ankles. Next, she undid her belt buckle and pulled it out, allowing her skirt to fall down to her ankles. Pretty soon, Rarity's pristine white derriere was in full view for Twilight.

"Oh…." The nerdy girl muttered, taken aback by the sight of her friend's rather large rear end. Little did she realize, she was enjoying this a little more than she thought she would.

"Ahem, are you ready Twilight?" The fashionista spoke up, breaking Twilight out of her mini trance.

"Oops, yeah." Twilight quickly responded, before approaching behind her friend, all while staring at her immense backside.

After snapping out of her trance, she quickly presses both her gloved hands against Rarity's hiney, letting them sink into the pure white flesh of her glutes.

The purple haired girl shivered when she felt the cold rubber from Twilight's gloves make contact with her bare butt cheeks. A strange sensation washed over Rarity while Sci-Twi experimented by grabbing and squeezing the flesh on both of her cheeks.

"Oooh." Rarity cooed, feeling weird yet slightly aroused by the feeling of her friend groping her big butt.

"Snap out of it Rarity! You're just helping your friend out." She thought to herself, forcing the perverted thoughts out of her head. As she struggled with her thoughts, Twilight continued to grab a hold of the soft, squishy, fat from the fashionista's sizable posterior. She ran her fingers up and down her sides and even pinched them a little just to see how much extra fat she had on, making Rarity squeak.

Then she moved her bottom flesh around, noting how the flesh bounced and ebbed while shivers shot through Rarity's body over and over. In fact, the nerdy girl had almost gotten lost in another trance, before she pulled herself back to reality.

"Alright, I think I've gotten enough results for this particular test." Twilight stated, removing her hands from Rarity's butt, but not before giving it a gentle squeeze. She quickly jotted down the details she had got from her little test.

"You… have?" Rarity asked, slightly surprised.

"Yes, now… you said your hips were how wide?" Twilight inquired.

"Uh… t-thirty-five inches…" Rarity finally spat out.

"I see…" Twilight muttered as she wrote it down. "Next, in order determine every aspect of your glutes every field must be explored."

"Field?" Rarity repeated.

"Yes. Touch, taste and smell." Twilight explained. "We've already done one via me feeling your rear all over, next… I will have to taste it."

"Oh… this is really necessary?" Rarity questioned, nervously and blushing red.

"Rarity, there's no such thing as useless information, even something as unorthodox and… disturbing, could be quite informative." Twilight told her.

"Oh, I guess you have a point there… Alright, as long as no one knows about this." Rarity told her, feeling a little worried.

"Thank you again, for agreeing to do this for me." Twilight said, smiling gratefully.

"So, I guess now we'll do the smell and taste test." The science girl rested on her knees, so that her head was level with the giant rear end of her friend. Seeing it up this close made the nerdy girl blush intensely, sweating while bringing her head closer.

Twilight caught a faint whiff of some sort of fancy shampoo, sniffing more to get a better feel of it.

"Wow… such a lovely smell… I was expecting something lewd but this…" Twilight remarked.

"Thank you, I do commonly use a flowery smelling body wash and that part does…" Rarity began. "Oh! Oh! Ooh!"

She was suddenly cut off when Twilight touched one of her cheeks with her tongue, dragging it up and down and licking it like it was giant scoop of ice cream, she even put part of it her in her mouth. She even suckled on her friend's plump rump cheek, savoring the flavor.

"Well, it seems someone is enjoying her research quite a bit." Rarity stated, causing Twilight to quickly remove her lips from her backside, blushing furiously.

"Sorry, I didn't mean to…." she began to say.

"Oh no, it's quite alright darling." The fashionista simply stated, smiling down at her nerdy friend. "You can even… kiss it… if you want to, that is."

"Really?" Sci-Twi asked, surprised. "Are-Are you sure?"

"Honestly… no… but Rainbow Dash and Pinkie Pie seem to enjoy it so…" Rarity started to say before she trailed off.

"Wow. This new interest is really opening your mind." Twilight remarked.

"That's… one way of putting it." Rarity admitted, slowly.

And with that, Twilight puckered her lips and kissed her friends rump. A light, wet sound was heard for a ten whole seconds before Twilight removed her lips and started planting multiple kisses Rarity's bottom. Some were pecks while others were long, loving kisses, like ones you give to a lover.

The fashionistas legs were beginning to buckle and shake from the attention her rear was receiving, like she was about to collapse, so Twilight quickly placed her hand on both ends of her posterior to keep Rarity still as she continued to smooch Rarity's butt and leave kiss marks all over it.

Soon enough, Twilight stopped, wiped her mouth and sighed. "Done… you ok, Rarity?"

Rarity tried to compose herself but remained in a blissful state. "Oh yes… a little wet… but otherwise ok… I think I'm beginning to love science…"

"Well… just to warn you… the next test will be painful…" Twilight winced.

"Oh, I'm counting on it!" Rarity smiled, full of sexual energy and ready for her next test or rather 'paddling'. "But first, I need to do something else."

Rarity quickly pulled up her skirt and undies, which confused the nerdy girl behind her.

"Wait, what are you doing?" Twilight inquired, curious as to what her friend meant.

"Before you punish me, I need to do something naughty." The fashionista spoke that last word with a mischievous glint in her eyes. Her eyes darted around Twilight's lab, before laying her gaze upon a wide window on one of the walls. A smirk grew on her lips as she approached it.

"Oh my, this window looks really clean." Rarity said, grinning even more.

"Oh yes, that's one of my observatory rooms, I make sure to clean the window of it every day." Twilight told her.

"It would be absolutely dreadful if someone were to smudge it up." The purple haired girl said, flicking her gaze back to Twilight while still smirking.

"What are you thinking…." Twilight started, before blushing intensely. "Oh, I see what you're getting at."

Rarity chuckled mischievously. "Yes, exactly. I am going to 'wipe my ass' with your window."

"Lovely…" Twilight said, with an awkward grin.

"Oh, and you are going to bare your rump as well." Rarity told her.

"Wait… what?" Twilight asked, shocked.

"Well, you can't exactly expect me to show you my derriere when I haven't seen yours. I can't be the only one half nude here you know." Rarity pointed out.

"Y-Yes, I understand but…" Sci-Twi stuttered.

"Yes. Butt. Yours. Show it." Rarity stated, firmly.

"Well… I… I'm not sure." Twilight stated, drawing it out and growing increasingly nervous.

"Look darling, it's only us two here. There's nothing to worry about. Also, your derriere can't possibly be larger than mine." Rarity said, making her friend blush again.

"I… I…" The nerdy girl stuttered, uncertain.

"Come now, don't you want to be more bold and daring?" Rarity inquired. "It could make you more like Princess Twilight if you did…"

Sci-Twi's widen hearing this. "Really?" she asked, intrigued. "Wait, I'll be more like Princess Twilight if I show you my butt?"

"No, I mean that if you do something as bold as this… you're confidence is sure to improve." Rarity reasoned.

"Well… that is possible…" Twilight admitted.

"Ooh, I know! Pretend I'm someone you really, really don't like." Rarity said, grinning.

"Someone I don't like?" Twi echoed.

"Yes, just picture me as him or her… then moon them! Trust me, it is quite the thrill." Rarity encouraged.

Twilight racked her mind for someone she didn't like as of lately. "Hmm, I guess maybe I don't like Principal Cinch?"

"Yes! Perfect! Pretend I'm Principal Cinch and moon me!" Rarity told her. "Bare your ass for all to see!"

Twilight blushed even harder, her mind was filled with conflicted emotions. Part of her felt extremely embarrassed to show her bare butt to her friend, but another part of her found the idea of mooning her previous Principal really exciting.

"Well… As long as no one else will know about it…" Twilight began.

Rarity shook her head. "Not a soul besides you and me."

The science girl adjusted her glasses, beginning to sweat nervously. "Alright, you're Cinch."

"Yes, exactly. Now let all your anger our, show me the moon!" Rarity declared.

"Okay, I guess it's worth a shot…" Twilight trailed off, before turning her back to her friend. She bent her upper body forward, effectively sticking her back end outwards. "Here goes…"

Twilight slowly unzipped her skirt, hooked her fingers under the waistband of her skirt and underwear and after taking a deep breath she sighed a long sigh as she pulled her bottom clothes down to her knees, exposing her naked butt to Rarity.

The nerdy girl's legs wobbled once she felt the cool air hit her bare ass. Her large purple posterior jiggled a little from the movement. Rarity gawked a little at first, surprised at just how large her friend's rear was but also quite aroused, having forgotten what it was like to be on the other end of a moon. She decided to encourage her more.

"That's right! Get jiggy! Shake your rear end! Raise the moon, Twilight! Raise it like you've never raised it before!" she exclaimed.

Twilight was quite stunned to hear Rarity say things that she would usually call 'balderdash' but since she had already exposed herself she couldn't let her friend down now.

The nervous science girl bent her knees a little more, while wiggling her tush from left to right. This made the fat on her ass cheeks move even more than before. As she shook it in front of her friend, a new excitement began to brew inside of her, making her heart flutter a bit.

"You see this Cinch?" Twilight said, really starting to get into it. "Well, guess what? You can kiss it! Because I'm done listening to you!"

"Yes!" Rarity practically squealed, getting into it herself. "Keep it up, darling! Oh… I'm getting so hot!"

Twilight smiled and continued shaking her big purple butt side to side. "That's right Cinch! Here's where you can place your lips! That also goes to every other Preppy in your stuck up school!"

"Atta girl Twilight! Swing that tush!" Rarity cheered. "Ooh! I-Dee-Ah! Let's press your booties together. You want to?"

Normally, Twilight would find this idea down right absurd. But right now, she was too lost in the moment to care. "You know what? Sure!"

Rarity giggled giddily, turning around and dropping her skirt once again, mooning Twilight for a second time before backing up and pressing her rump against Twilight. The two of them shivered as they felt the sensation.

The two begin to rub, squish and grinded their rear ends together. The flesh on both goes up and down and then twists a bit as the owners made their butts rub around each other's in complete circles, with one going left and the other right. They giggled and cooed as this happened.

The two then leaned forward and begin to bump butts with each other over and over again. The flesh on both of their butt cheeks wobbled all over, filling the two girls with even more excitement.

"I'm enjoying this way too much… But I don't care!" Twilight declared, giving her butt another bump against Rarity's, so hard in fact that it pushed her forward.

"Ooh! That's quite a lot of muscle in those glutes of yours." Rarity remarked.

"As well as fat, don't forget that." Twilight reminded, cupping both her chubby cheeks.

"Well, at least it's not as big as my derriere." Rarity confirmed it by grabbing ahold of one of her cheeks, her hand barely covering one of it.

"Ooh! Suddenly I cannot wait to spank it!" Twilight grinned before composing herself and trying to look profession. "Ahem. In order to test it's tolerance for pain that is, see how long it takes for it to turn red."

"Oh, so you want to spank my naughty tush?" Rarity said, a wonderfully mischievous little idea forming. "Well, try and spank it when I do this!"

The fashionista quickly dashed to the observatory room's window, turning around and pressing her derriere right up on it. The cold chill from the clean glass made Rarity shudder with excitement.

Twilight suddenly got curious and ran through a door that led to the room. Soon, she appeared on the other side, witnessing Rarity's two massive white globes flattened up against the window.

"Oh… So that's how it looks." Twilight muttered, in awe. Her eyes follow the two cheeks as they moved left, right and up and down.

Rarity peeked behind her and found Twilight staring intently, making her naughty smirk grow. "I see someone is enjoying the full moon." She muttered to herself as she backed up more, squishing her fat butt cheeks even more against the glass, wiggling it while she did so. Memories of mooning that one store suddenly flooded back into the fashionista's mind, making her laugh a haughty laugh.

Meanwhile, Twilight was getting the show of her life. Watching Rarity press her ass against the glass in front of her made her so hot she was tempted to pleasure herself right then and there.

"Mmm…" Twilight moaned a bit, biting her lip. "I need to cool off."

She grinned as another thought entered her brain. She quickly turned around and pressed her rear against the glass as well, directly on the spot where Rarity's was. The two asses overlap each other, with Rarity's still being a few inches larger and only the glass separating them.

Both of them rubbed their rears up in down in unison with each other, creating loud squeaky sounds that echoed throughout the lab. Both of them could nearly feel each other's tushes through the glass as well.

"Ooh… so cold… so good…" Twilight sighed, blissfully.

It wasn't until one of them removed their tush from the window to inspect the glass.

"Oh my…" Rarity stated, staring at the giant print her two cheeks made. Twilight noticed her friend had stopped and removed hers as well, checking the results.

"Wow… I didn't know it was that big." Twilight said, another blush forming when she noticed her butt print was just a few inches smaller than Rarity's. She left the observatory room and approached Rarity.

"Did you enjoy that as much as I did?" Twilight inquired.

"Oh yes, darling. Very much so." Rarity replied, her butt cheeks still a little chilly, and even slightly sore after pressing them against the window for that long while her cheeks were beat red like Twilight's.

"I had no idea this kind of thing was so much fun." Twilight smiled.

"Neither did I. I suppose we both have to thank Rainbow Dash for this." Rarity remarked. "Somewhat disturbing but I can look past it."

Twilight giggled. "Yeah, now I can see why Rainbow gets so much enjoyment out of mooning people."

"Indeed, it's like… after I did it once… I wanted to do it again and more!" Rarity expressed before turning around and spanking herself in front of Twilight. "Much more."

"Ooh…" Twilight cooed, watching the flesh of Rarity's rump jiggle rapidly.

"Are you ready?" Rarity inquired, smiling.

Twilight nodded. "Absolutely!"

"Excellent!" Rarity said, pleased as she walked over to a desk and bent over, proudly baring her rump and shaking it, eager to be spanked.

"Oh, someone's being naughty." Twilight smirked before heading over to another desk and grabbing a ruler from it. She smacks it against her other hand as she slowly approached Rarity.

Next Chapter: Chapter 11 Estimated time remaining: 4 Hours, 20 Minutes