You're asking me to do WHAT?!!
"A-ah, Twily..."
Shining stroked his sister's mane as she sat on his penis, feeling his whole length cradling inside her warm, moist cervix. The tip of his penis was deep into Twilight's womb, and now it was flaring in its full bloom, desperate for release.
"Oh, S-Shiny!" Twilight gasped in ecstasy and hugged her brother tighter, "Please... Fill me! Fill my virgin pussy! I want you to claim me!"
"A-ah! Twily... I'm gonna... Gonna!"
Shining started pumping himself harder, feeling his cock hitting the back of Twilight's womb. His tightening balls hit Twilight's perineum as he pushed himself in with full force, making them both scream from the top of their lungs as they reached their climax together.
"I'M CUMMING~!" Shining moaned vocally as he filled his sister's small womb with his thick, warm batter.
She was not going to survive! She was definitely going to get pregnant from this, she was going to bare his foals as a sign of responsibility and love. Her virgin body, now deflowered, her womb becoming fertile.
His sweet little sister was going to be a mother.
And he was the father!
And then...
Shining's eyes shot open!
Having just woken up from a daydream, Shining looked around to inspect the results of his intense orgasm. He was panting to catch his breath and glanced at his hoof, seeing it dripping with his seed, having just blown a massive load in his frog.
"Sweet Celestia!" He blurted out in post-orgasm clarity and shame, "I did it again!"
Some time later it was a brand new day in Canterlot. Shining Armor was preparing for his own wedding, that had been postponed to the next day after a sudden siege of Chrysalis and her Changeling army.
After asking for her little sister to become his best mare, he thought he could finally focus on the preparations without being distracted, knowing that Twilight took organizing a lot, lot more seriously than himself. However, instead he was being asked a question he wasn't ready for at that moment...
"Huh! You're asking me to do WHAT, Twily?!" Shining almost yelped in confusion after hearing his sister's request.
"An urine sample!" Twilight repeated and smiled, "As in, peeing in the cup!"
"Don't be ridiculous, Twily!" Shining said with a stern look, "You couldn't possible ask me to-!"
"As your best mare, I'm obligated to make sure everything goes fine. And I mean EVERYTHING!" Twilight replied, returning a stern look at Shining, who was taking a little aback by her reaction, "I have to make sure you are totally, and I mean, TOTALLY healthy before that ceremony of yours!"
"Y-yeah, I know you want to be thorough..." Shining was getting nervous, "But... Are you even a licensed nurse to do this?"
"Actually I am!"
"W-what?" Shining was more than surprised, "When did you-?"
"As a student of Princess Celestia, you learn all kinds of things!" Twilight beamed and held out a sample cup for her brother, "Now, just pee in this cup and we're good!"
"Umm, Twily... Is this really necessary?" Shining Armor asked his little sister timidly, with a very confused look on his face. Even if it was something natural he had no difficulties of doing, it felt weird to urinate right next to his sister of all ponies.
"Are you a chicken, Shining?" Twilight suddenly asked with a smirk, knowing very well that her brother was in for a challenge.
"What... No... NO WAY, Twily!" Shining replied slightly offended, "I am the captain of the royal guards! Of course I'm not a coward!"
"Indeed! And as the captain, you also know you will do whatever it takes to protect your kingdom!" Twilight said sternly, "Meaning... Everything . Aaaand... Since I'm the only one around, I have to make sure you undergo some of these mandatory medical examinations!"
"Y-yeah, I know!" Shining looked away, "This is just... So damn weird..."
"Please, Shiny! Let me help you!" Twilight pleaded with a pout, "It was Cadence who asked me to do this, after all!"
"H-huh? Cadence?" Shining batted his eyes, "Is she THAT worried about me?"
"Well, of course! She loves you!" Twilight replied, "She didn't have heart - or a licence to be frank - to do this herself. That's why she asked me to examinate you. As your best mare! And... Your sister..."
Touched by Twilight's annoyingly adorable puppy face, Shining sighed in defeat and reached out his hoof, "Give me that cup! Just... Let's get this over with!"
"Sure, my brother!" Twilight chirped, "Here!"
Shining grabbed the sample cup from Twilight's hoof and positioned himself over the toilet. He aimed his unfurled member towards the cup and tried to relax. He knew he had done this before many times, this time was just a tiny bit of different than before...
It was his sister watching him...
"Wait!" Shining realized something, "How come you have a medical licence but Cadence doesn't? Weren't you both Celestia's students?"
"Does it really bother you, Shining?" Twilight asked, making Shing roll his eyes.
"Nah, forget it!" He said and lowered his gaze. He was still sensing Twilight just a foot away from him and it made him feel a little uncomfortable.
"Umm... Do you really have to watch me doing this, Twily?" He asked in confusion, "This is not a drug test!"
"Unfortunately I have to, Shining." Twilight replied as professionally she could, "I need to make sure that your... Ahem, penis... Works perfectly fine before you meet your wife-to-be. I mean, there could be changeling eggs or something. We need to be sure that you're healthy."
"I... I think my penis works JUST fine, Twily!" Shining shook his head, "You just really want to watch me pee, right?"
"Is there a problem in that, Shining?" Twilight asked cheakily, "Don't worry, I've seen you doing it before, you know. We grew up together, remember? Remember that one time when we were foals and you told me to open up my legs so you could-"
"Twily! Please, please don't mention that!" Shining closed his eyes in shame, "It was so embarrassing! And we were kids back then!!"
He then tried to look away, averting his sister's gaze as he tried to go, "I mean... It just feels so weird to do it in front of you! You're... You're my sister after all!"
"I know, Shining," Twilight reassured, "But I'll promise you I won't tell about this to anypony, EVER! This is just between the two of us. And... We have a plenty of time. I can wait!"
Shining sighed and turned his head back to his hose, adjusting his aim to not miss the sample cup.
"I'm doing this for you, Cadence..." Shining reassured himself and managed to relax. Soon a trickle of urine erupted from his urethra, a tiny noise filling the room as the cup in his hoof started to fill. Soon it grew in volume and pressure, turning into a heavy stream that splattered everywhere, and it didn't take long for him to fill the cup to the brim. He moved the cup away from his stream and held it out for Twilight as he repositioned himself to keep urinating into the toilet.
"Here you go, Twily!" Shining said embarrassed, turning his gaze towards his stream to watch his aim, not wanting to be any more bothered about his sister's presence.
"Oh gosh, Shining! That's a pretty good sample!" Twilight giggled as she felt the warmth of Shining urine through the cup, then levitating it on the table next to her, "Well, I'll take care of this!"
She then turned back to Shining, who still continued to go with droplets of his piss splattering everywhere.
"When it starts, you can't stop, right?" Twilight asked and winked.
"Y-Yeah..." Shining replied quietly, his cheeks glowing red, "Been holding it for a while!"
"I bet!" Twilight replied and turned towards Shining's sample, "Don't worry, I won't judge! Yet you REALLY don't have to be embarrassed! I've never seen anypony bigger than you!"
"Why, thanks..." Shining muttered as an awkward silence filled the room, knowing she was just flattering him. For a while, the only sound to be heard was created by Shining's urine hitting the water.
After a moment that felt like an eternity for Shining, he let out a sigh of satisfaction as his stream stopped, finishing with a couple of spurts into the bowl. Twilight kept watching as her brother shook himself off, flopping his schlong like a slab of meat.
"Oh yes! Shake your tool, Shining!" She whispered huskily, eyes locked in her brother's waving junk.
"What was that, Twily?" Shining asked curiously as he finished and lowered the seat.
"Oh, nothing!" Twilight chirped, "Just... Keep on doing what you were doing!"
Shining shrugged as he flushed the toilet and turned to face his sister.
"What now, Twi-?" Shining couldn't even finish his sentence when Twilight reached her hoof towards him, holding another sample container.
"I need you to give a semen sample!" She announced cheerily, "Just in case!"
"W-what?!"
"You know, Shining. I have to make sure you don't have any larvae or eggs in your testicles!"
"Eugh, gross!" Shining replied in disgust, "Is that something changelings would normally do?!"
"Well, we really don't know!" Twilight shrugged, "That's why we need to be extra thorough!"
"Fine, I'll do it!" Shining shook his head, "It's still better than having eggs in my balls!"
Shining grabbed the sample cup and turned around to face the toilet bowl once more. His limp penis started to harden, turning into a thick tube of flesh, almost as big as Twilight's leg. He then casually grabbed his erect member and shook it a couple of times, his shaking transitioning into jerking as he soon clopped himself furiously.
"Mmm, nice... " Twilight bit her lip while watching yet another erotic display in front of her. "Jerk it good, Shining!"
"Nngh! Guh!" Shining grunted when he came, shooting a thick rope of creamy cum into the cup, then moving it away as he kept ejaculating into the toilet.
Twilight's eyes shot open as she watched Shining's pulsating member as he kept cumming, not wanting to miss such a show she was privileged to witness!
"Ok, here you go, sis!" Shining huffed, shaking a strand of cum off his member as he held the cup.
"Oh! Thank you, Shining! I'll take care of this!" Twilight repeated her actions while Shining was ready to leave.
"Ok, are we done already-?"
"I need to perform sounding as well!" Twilight informed, "To locate obscurities of any kind in your urethral tract!"
"TWILY!" Shining shouted in frustration, having gotten bored with his sister's requests.
"This is necessary, Shining! I NEED to make sure you're in good condition!" Twilight explained, but Shining had already had enough.
"Twily! I AM NOT GONNA TAKE PART IN YOUR SICK EXPERIMENTS!" Shining said calmly, "I've got a wife to marry and I really, REALLY have to go now and prepare for-!"
But soon as he was leaving, an oh-so-familiar cloud of magical aura engulfed him all over, and he was levitated back into the bathroom.
"N-nooooooo!!!" Shining cried out as he was slammed flank-first on the toilet lid.
"Oh, don't worry, Shining!" Twilight reassured, "I'll make sure it doesn't hurt. It's just a matter of proper lubrication!"
"L-lubrication?" Shining asked in horror, "What are you going to insert in my...?"
"Oh! It's nothing special, I'm just using this!"
After saying that she pulled out a foot-long metallic sounding tube, making Shining's pupils shrink at the sight.
"Eep!"
Shining could only watch in a complete horror as Twilight took his junk into her hoof and started shoving the metallic rod into his urethra, a sharp tingly feeling filling his most sensitive organ as it was pushed deeper and deeper.
"A-ah! Ngggh!!!" Shining gritted his teeth while feeling the weirdest, most extreme new sensation of sexual gratitude he had ever felt, as more and more of the tube was shoved deeper into his "pee-hole". His cock grew into the full mast in an instant, throbbing along with the intense feeling as the insides of it were scraped by the rod.
Twilight leaned closer and gave Shining's member a lick, making him jolt.
"Gh-huh? Twily?" He stammered, but Twilight turned her head to look at him and shushed.
"Just relax, Big Brother!" Twilight said softly and licked her lips, soon returning to worship her brother's turgid cock as she kept performing her medical procedure, "I'm just helping you cum..."
"Uh, i-it doesn't work like- Ugh!"
Twilight licked and kissed all around Shining's throbbing cock, jerking the sounding rod deeper into his urethra and coating her brother's most valuable asset in her saliva, droplets of spit trailing down his shaft.
Shining squirmed in his sister's hold, gritting his teeth in a mix pain and pleasure. He felt like the metallic rod was milking him with its motions and soon it passed the point of no return as his cock erupted with another cumshot.
"GHAA-HAAAAAAH!!! NNGHHH!" Shining grunted loudly, and to his sister's surprise, the rod shot out of his cock with the force of a bullet, traveling throught the air like a projectile shot out of a railgun and ultimately hitting the door with a bang and piercing it!
"Oh my!" Twilight watched it in awe, unable to come up with any kind of suitable quip.
"Aah, don't shoot! DON'T SHOOT!! I SURRENDER!!" A feminine, adorable voice suddenly came from behind the door as it opened and somepony entered the bathroom without permission.
Shining's eyes shot wide as he noticed who it was: his wife, Princess Cadence, had entered the room in a hurry and almost slipped on his cum that he had spurted on the floor, skating around for a moment until readjusting herself gracefully.
"Wha- C-Cadence?!" Shining was shocked, staring at his wife who was now standing right in front of him. He tried to cover his throbbing, still-spurting cock behind his forlegs and stammered, "This... This is not what it looks like, Cadence! I swear!"
Cadence stood before Shining and Twilight in silence, looking at them sternly. For a moment, Shining thought his marriage was over, but then Cadence bursted into laughter, much to his confusion.
"Oh, Shining!" Cadence laughed, "You really think I'm that stupid? Of course I know what that looks like!"
Her expression changed into a smug.
"Just like I asked for!"
"W-WHAT?!!" Shining exclaimed as he put pieces together in his mind, "D-did YOU ask Twily to do this?!!"
"You see, Shining... I know you and your sister have feelings towards each other." Cadence explained, making Shining blush.
"N-no! I mean... Not THOSE kinds of feelings!" He protested, "I swear-"
"Oh, please! You cannot hide that from me, Shining! I'm the Princess of Love after all!" Cadence enjoyed every second of roasting her husband, "I know you want to fuck your sister!"
Shining covered his eyes in shame, his biggest secret now having been revealed. Twilight blushed as well, but not in shame.
"Oh my! I guess the feeling WAS mutual, after all!" Twilight smiled.
"But I won't judge you!" Cadence reassured happily, "Your little sister is indeed very precious! I know you've been desiring to have your way with her... BUT! You never dared to touch her, regardless!"
"Huh? You... D-don't hate me because of that? B-But, I just-!"
"Shhh! It's okay, Shining!" Cadence started stroking her husband's cheeck, "I'm not angry or disappointed! In fact... I would TOTALLY watch you two having sex! Just like I loved watching you two playing doctor!"
"W-what?!!" Shining was dumbstruck, "W-What was that, Twily?"
He looked at his sister in an utter confusion, "Were you... Together in this?"
"Yes! Just a prank, bro!" Twilight giggled and winked at her brother. "She told me she had a thing for playing doctor with stallions, but..."
She turned to look at the blushing Cadence next to her.
"Well, I kind of... Chickened out!" Cadence grinned nervously, "I couldn't dare to ask you, so I... Well, how do I say this..."
"So you asked my sister..." Shining said in a mix of disgust and confusion, "MY VERY OWN SISTER, of all ponies, to live out YOUR sexual fantasies!"
"Umm... Yes!" Cadence said embarrassed, "Because she knows you better than anypony else. And... Because I trust her."
She then started giggling happily, "And you know what... I bet you enjoyed it as well!"
"Huh? N-no! I didn't!" Shining stammered, "She's my sister! I... I couldn't possibly..."
"Oh, please, Shiny!" Cadence smirked, "I'm The Princess of Love, remember! I can sense everypony's love towards each other. The genuine kind of love, no matter what happens..."
She then glanced over Shining junk, which was having a mind of its own, as it was getting bigger and bigger without Shining noticing.
"Oh please, save that for the honeymoon, Love!" Cadence giggled and turned her gaze back to Shining, "I'm expecting you be quite ready for some fun after the wedding's over. I can't wait as well! To enjoy that lovely cock of yours!"
She gave Shining a kiss on the cheek and turned around to leave, swishing her tail to the side for a brief moment, flashing her drenched marehood towards Shining's direction.
"See you soon, my love!" She said with a wink and left, closing the door before their eyes.
Shining batted his eyes for a moment, turning his head back to Twilight after a while.
"W-what was that all about, Twily?"
Twilight looked away and blushed. "Well, I'm... I'm sorry I didn't tell you beforehand, Shining! It just... It was so priceless!"
She then looked at the sample cups on the desk and blushed, "And I have to admit, you took it pretty well! I'm so proud of you, big brother!"
"Well... Thanks, Sis..." Shining sighed in defeat, but also in relief. Despite his fears, his sister wasn't trying to seduce him, or trying ruin his marriage before it even started. And he hated to admit it, but he had indeed enjoyed it as well! He wasn't sure if he could ever have normal married sex with anypony after such an intense sounding session!
"You, Twily... Are something else!" He said and laughed, shaking his head at his sister's antics.
"I know, Shiny!" Twilight giggled and put her hoof on Shining shoulder, "Now let's get you cleaned and ready for your big night!"
-The End-
Author's Note
Don't ask... 
