Twilight paced back and forth inside her throne room. She recently finished her latest research tool, but she had no test subject. Twilight never enjoyed using live subjects, but what could she do? A live specimen was necessary, it simply couldn’t be avoided. And she couldn’t let the potential information go to rest, the research had the potential to benefit ponies for years to come. One way or another, Twilight would have to find somepony to use. More than likely, it would have to be one of her friends.
Twilight sat on her designated throne and pondered who would be the best pony to ask. It sadly had to be a pony, because she was certain Spike would volunteer if asked. Pinkie pie was automatically out, she was too much of an outlier. Twilight couldn’t tell which results were from the test and which were just Pinkie being strange. Fluttershy would never go for it. Rainbow Dash would likely agree if Twilight dared her to, but she would try to act tough and likely throw off the data. Applejack might say yes, but her Twilight really did not wish to ask her. Her job required intense physical activity. Twilight wouldn’t want Applejack to miss any work because he body was too damaged from test. Thus, the only pony left to ask was…
“Twilight! Are you here?”
As if on cue, Rarity galloped through the throne room doors. She saw twilight on her seat and smiled widely.
“There you are! I just had to thank you so much for helping me land the clothing deal with Saddle Arabians.”
Three days prior, Twilight and her fellow princesses meet with dignitaries from Saddle Arabia. At one point in the conversion, the female ambassador mentioned that ponies from her land raving over Sapphire Shores’s outfit from her latest concert. Twilight then mentioned that it was her friend Rarity who made those outfits. One thing led to another, and the meeting ended with the dignitaries agreeing to contact Rarity about making some outfits in the Saddle Arabian style to sell in their stores.
“I’m guessing they contacted you?”
“Spikey-poo just showed me the letter! They’ve agreed to pay for a whole line! Can you believe it, my work will be in stores from the other side of Equestria!”
Rarity bounced to Twilight and embraced her in a tight hug.
“Oh thank you, thank you, thank you Twilight! You done me the greatest favor possible! Oh, if there is anything I can do to thank you, please let me know! I mean it, absolutely anything!”
Twilight returned Rarity’s hug and looked Rarity in her blue eyes.
“Oh Rarity, you don’t need to thank me. You got that line based on your own merit. I don’t deserve any credit.”
“Nonsense! You were an enormous help! I simply must pay you back. Surely there must be something I can help you with, anything!”
Twilight scrunched her face and turned her eyes away. “Well, there might be something…”
Rarity let out a chuckle. “I knew it! Whatever it is, you have my assistance.”
“Rarity, you don’t even know what it is yet.”
“It doesn’t matter, darling. I will put in my best effort to aid you, regardless of the task. You have my word.”
“...do you really mean that?”
Rarity placed a hoof on Twilight’s shoulder. “By Celestia’s mane, I do.”
Twilight smiled warmly and sighed. “Ok then. I actually do have a problem, and I was actually considering asking you anyway.”
Rarity sat down on the diamond throne and crossed her forelegs rested her head on them.
“I’m all ears. What do you need help with?”
Twilight returned back to her own seat and closed her eyes before recanting. “As you know, we and our friends tend to get into a handful of fight.”
“More than most ponies go through in a lifetime.”
“Exactly. And with our new castle and my new status, we will most likely encounter even more fights. So I figured that it’s in our best interest to have some extra protection.”
Rarity nodded. “That would be nice.”
“Right. So for the past week, I’ve had Cadence help me adapt her ‘protection bubble’ spell. I picture I can alter it from shield my to creating personal barriers around all of us.”
“Oh! That sounds most impressive!”
“Thanks! So, I’ve been practicing the spell on myself for the a while. All was going while, until I found out an error.”
“An error? Like What?”
Twilight blushed and turned her face to the side. “The spell provides adequate protection over a ponies body, except for a certain… part.”
“Certain part?”
“The spell is too weak on a certain body part. A lower body part.”
Rarity blinked in confusion. “Lower body? You mean the legs?”
“Noooo.”
“The back?”
“Close. A bit further down.”
“Further down. You don’t mean the…” Rarity noticed Twilight’s rosy cheeks, which affirmed her thoughts.”
“...you mean the flank, don’t you?”
Twilight didn’t face Rarity but nodded. “That’s correct. For some reason, the barrier around the flank is too weak. It barely provides any protection.”
Rarity looked at her friend with slanted eyes as she began to work out what help Twilight was asking for. “So when you say you need help…”
“I mean I need to make use of your hindquarters. That would be the gist of it.”
“...Oh” was all Rarity could respond. Knowing Twilight, she was prepared for an odd request, but this took the cake. Twilight wants to make use of flank? To do what with it?
Twilight coughed into her hoof and continued. “Obviously, the key to fixing this problem is gather more information about that area of a pony under strenuous actions to further alter the barrier.”
“...um, can you translate that into layman’s terms darling?”
“I would need to perform stress test on your rear end.”
Rarity never imagined hearing that sentence. “What… kind of test?”
Twilight turned back around at the chance to explain something. “Basically, I would perform particular actions on your rump and record your reactions.”
Rarity raised her eyebrows. “What kind of reactions.”
Twilight again turned away from Rarity. “Your… level of pain.”
“PAIN!” Rarity shouted. “Why would I be in pain?!”
Twilight recoiled back from the outburst. She held up her front hooves in front of her face.”I’m sorry! I’m sorry! But for the test to be practical, we’ll have to make the test strenuous on your flank! The barrier needs to be able to protect from hard hits, therefore your flank has to be hit hard.”
Rarity’s pupils shrunk into her eyes. She meeked out in a quiet voice, “hit? you plan to hit my flank?”
Another sigh. “Yes. I broke the tests into three parts to test the range of resistance: a hard edged force, a hoof strike with an instrument, and a puncture force.
Rarity gulped. Beads of sweat slid down her face. “And in what way to do you intend to test these parts.”
Twilight finally grew the courage to look Rarity in her face to answer. “By spanking you, caning, and hitting your behind with a miniature cactus.”
Five minutes later, Rarity awoke laying on a pile of pillows. She was covered by a purple blanket and felt a cool breeze fanning her. She looked up and saw Twilight levitating a fan to blow on her.
“How do you feel, Rarity?”
Rarity opened her eyes and stretched out her legs. “I feel fine, darling? Um, why am I laying down on this dirty floor.”
“Sorry, I didn’t want to move you after you fainted, so I just placed the pillows under you.”
“Fainted?”
Twilight gulped again. “Yes. You passed out after I explained the resistance test to you.”
The conversation flooded back to Rarity. “Oh yes, I remember now. There was talk of spanking and caning and….”
“And a cactus.”
“Oh yes, and a cactus.” Rarity nerves returned. “And I assume these tests are absolutely necessary.”
Another sigh. “I’m afraid so. This barrier is very important to me. I can’t bear the thought of my friends in danger when there is something I can do to help them. This shield could potentially save one of our lives. Besides that, other unicorns could research the spell and use it themselves. This has the potential to revolutionize defense measures for years!”
By now, Rarity was used to Twilight’s enthusiasm towards scientific discovery, but she was still amazed by her friends determination. She always worked hard to help others, even as a princess. Twilight was always there for her friends, so it’s only fair that her friends return the favor.
“This is important to you, isn’t it darling?”
“Very. I really, really want this to work out.”
Rarity shut her eyes and took a deep breath. Sh breathed out the last of her hesitations.
“Ok then. I will help you.”
Twilight’s eyes filled with stars. “Really?! Do you really mean it, Rarity?!”
“I do. If it’s to help you and our friends, a little… posterior pain is worth it. I’m in.”
“Oh thank you Rarity!” Twilight said as she embraced her unicorn friend. “Trusts me, this won’t take long. We can finish it today, in fact!”
“Really? That quickly?”
“Oh yes! I just need to inflict pain on your rear end and chart your reaction. Easy!”
Rarity gave a dry chuckle. “Well if that’s all, then I guess the sooner this is done the better. Let’s begin.”
Twilight clapped her two hooves together. “Great! I just have to do one thing.” A purple light temporarily blinded Rarity as Twilight teleported behind her. She then squeaked as Twilight ran a hoof over her flank, down the diamonds on her side.
Rarity blushed and stammered, “Twi-Twilight! What are you doing?!”
“Before the tests, I need to understand the body part, to build a baseline. It won’t take long.”
With that, Twilight inspected Rarity rear with her patented scrutiny. She ran her hooves up and down her sides, taking time to trace slowly trace her cutie marks. Twilight brought her face closer and rubbed her cheek on Rarity’s cheek. Then she moved her bottom flesh around, noting how the flesh bounced and ebbed.
Rarity stood still during the inspection, but shivers shot throughout her body. The only time a pony paid so much attention to her flanks were at the spa. Twilight’s such touch and care gave the two a run for their money. She closed her eyes and soaked in Twilight’s pokes and prods. Maybe these tests weren’t so bad, if they led to more of this.
“All most done, Rarity. Just one more thing.”
“Oh, take your time darling. Honestly, I rather enjoy the… AHHH!” Rarity shouted when she felt cold, wet sensation on her flank. She turned around to see Twilight licking her rump.
“Is-is this really necessary, Twilight.”
“Of course. There’s no such thing as unnecessary data. We need to gauge all the aspects of your rear, including taste.” Twilight returned to her task and slurped Rarity butt. IT was if Rarity’s flank was an ice cream as Twilight dragged her tongue up, down, and around the rump. She took extra care to swirl her tongue on her diamonds, earning soft moans from Rarity.
To finish up, Twilight puckered her lips and kissed the rump.
*pop*
A light sound was heard as planted kiss after kiss on the bottom. Rarity’s legs were beginning to buckle from the attention, so Twilight placed her hooves on both ends of her posterior to steady Rarity. She continued smooching Rarity’s butt.
*pop*
*pop*
*pop* *pop* *pop*
With one last kiss, Twilight let go of Rarity. The unicorn was going to collapse but Twilight caught her in a purple aura. Twilight wiped her mouth and went around to face Rarity.
“Are you feeling ok, Rarity?” Twilight asked.
Rarity took a moment to compose herself from her blissful state. “Oh, yes. That was quite the experience. I think I may want to pursue a career in the sciences myself.”
Twilight giggled, “Good to hear.” But he smile faded and her face turned to gloom. “Truth be told, that wasn’t for research. I just wanted to make you feel good before we start. Because trust me, the next experience will be far from pleasurable.”