For Science!

by FinnBeenie

Rating: mature
Tags: Romance, Porn, Sex, Fetish, Spike, Profanity, Slice of Life, Twilight Sparkle, My Little Pony: Friendship is Magic
Length: 3934

Twilight caught a grown-up Spike looking through her toy stash, and learns a particularly interesting fact about male dragon biology

Twilight caught a grown-up Spike looking through her toy stash one night. She questioned him, and learns about a particularly interesting fact about male dragons: the slit which usually contains a male dragon's member can be used for penetration. With Spike intent on exploring his body, Twilight's curiosity got the best of her and she insisted on observing. What started as scientific curiosity around dragon biology quickly led to much... hotter feelings in her, as she gets roped in deeper by Spike's needy moans.

(More chapters to come, maybe, in the future)

Contains: bottom Spike, biting, pseudo-incest?

Cover image cropped from Prismrti's post on twitter.

Published 2024-10-27 20:30:01 UTC
Last updated 2024-10-27 20:30:01 UTC

Late-night experimentation

“FINALLY! That’s everything for today!”

Twilight Sparkle stretched out her hooves and yawned as she stowed away the paperwork before her. It’s been a busy day, but that sums up just about every day now for her. Years have passed since her coronation as the ruler of Equestria, but trying to adjust to the monumental amount of bureaucracy and paperwork that comes with the position is still an ongoing process for the young princess, not to mention her teaching duties on top of everything. It's a good thing it’s a weekend tomorrow so she can take some time to recover.

Her old mentor Celestia has been... less than helpful with her advice, to put it politely. “Everything will work out if you just BELIEVE!” Although she meant well, that’s not really Twilight’s way of doing things. Although she’s been barely managing to hang on, this new lifestyle didn’t allow for much spare time for her to pursue her interests and hobbies. It’s not a huge deal, but she’s been missing those days when she would spend hours digging through old academic manuscripts and researching new spells in the library.

Twilight cast an organizer spell to tidy up her study as she closed the door behind her. She strolled along the long hallways leading to her bedroom on the other side of the castle, feeling exhausted. Everything in the royal castle was much bigger than her tree in Ponyville, as they were built to accommodate fully grown Alicorn. Although Celestia and Luna told her the growth spurt would come very soon, Twilight is still at her regular pony size for now. Inadvertently this meant the walks between every room were that much longer, especially after a long day.

As Twilight finally arrived at her bedroom, she noticed the door slightly agape, and the lights were on inside. She peeked through the crack, and a familiar figure popped into view. It was Spike, her number 1 assistant, and he appeared to be... rummaging through her drawers?

“What are you doing Spike?” Asked Twilight, as she entered her room. It’s pretty late already and he’s usually in bed by the time she returns every night, not to mention since his little growth spurt a while back he asked for his own room across the hall, so he doesn’t even sleep here anymore.

“No... nothing!” The purple dragon jumped, quickly hid something behind his back, slammed the drawer closed and turned his head immediately to Twilight. “You... you’re back early tonight!”

“It’s almost past midnight already! What are you doing in my room...” Twilight paused as she noticed a little... pink thing, accidentally peaking out behind Spike’s back as he clumsily tried to hide whatever he was holding from her. She glanced at the drawer by his legs, and it clicked. “Did you go through my... stash?”

“Wait! I can explain!” The purple dragon is heavily blushing now, “Please don’t get mad, I was just...”

Twilight wasn’t mad, really. She found it quite endearing to watch Spike stumble over his own words trying to explain away the embarrassment.

“Hey Spike, that’s okay! You know you could have just asked!” She tried to calm him down a little, it was a memory all too familiar to her, and she didn’t want to make it too embarrassing for him.

“You’re not... mad?”

“Of course not! I mean, you’ve grown a lot, and as with growing boys your age of course you will have... those urges, so it's nothing to be ashamed of! But I’m surprised, I never knew you were into stallions! You were all over Rarity a couple of years ago!”

“It’s not like that! Really! It’s...”

“Hey, it’s okay! Remember what Cadence says all the time? Love is love!” Twilight said as she moved closer to Spike.

“NO! Really! It’s... not that!” Spike meeped as he chucked the pink dildo onto Twilight’s bed. “It’s... promise me you won’t laugh if I tell you, okay?”

“I promise!” Twilight gave him a soft pat on the back with her hoof. It’s pretty hard to reach now with how tall he’s grown.

Spike sat down beside Twilight and glanced at her. She gave him a firm nod.

“So... Smolder and I were chatting the other day when she came to visit, and... somehow we got to the topic of...” Spike made a pumping motion with his claw, which Twilight immediately understood. He continued, “Smolder said it’s possible to stick something in the front here... and how ‘all the dudes back home are doing it’... so I wanted to try it out.”

Twilight was intrigued. “Oh! I.. eh, didn’t know that about dragons! How fascinating!” She fetched a notebook and quill from her nightstand and noted it down.

Spike hid his face behind his palms. “...Yeah, I thought maybe I could borrow one of your toys. I’ve never done it like it before.”

Twilight chuckled lightly, finding Spike’s shyness quite endearing.

“Hey! You said you wouldn’t laugh!” Spike looked a little annoyed.

“Sorry! Sorry! I wasn’t laughing at you! But really, you could have just asked. I would have bought you some new ones from Zecora!” Twilight replied.

But just then, an idea popped into her head. Without much thought, she blurted out a shocking request.

“Spike, is it okay if I... observe you?”

“WHAT? Are you serious? That’s...” Spike was taken aback by such a brash statement from Twilight.

Some common sense came back to the purple pony after hearing Spike’s response. She frantically tried to clarify. “No, it’s not like that! I’m just curious about... how that actually works? I just... really want to know how dragons work, and this is a really good opportunity. I know it’s awkward, and you can totally say no if you don’t want to!”

Spike sighed out loud. He could see the curiosity-fuelled excitement radiating from the purple pony. He had always seen Twilight as her big sister, which made her proposal extra awkward. But Twilight also never shied away from the topic of sex with him once he grew up, giving him sex ed lessons and such. She’s also got more experience with... those toys, and he could benefit from some guidance for his first time. Plus, he had a hunch she’s going to ask him again down the road. He knows well how unwavering her curiosity can be.

“...Fine, you can watch. I do need some help with... my first time, I don’t want to accidentally hurt myself.” On some level he still couldn’t believe he gave her ridiculous proposal a serious consideration, much less agreeing to it.

“YES! Thank you, Spike!” Twilight gave the dragon a big hug. Her excitement helped to dispel some of the awkwardness. She had gone through almost every single book in the Canterlot Grand Library, and she doesn’t remember there being much about dragon biology at all. No surprise, really, with relations between the two species only improving recently. But, that is about to change. This is a rare opportunity to investigate dragon intimacy! She eagerly opened her stash drawer, fetched a bottle of clear lubricant and a smaller-sized toy with her magic, then set both down on her bedside table. “So, first things first...”

“WAIT!” Spike yelled, his face practically boiling. “...Give me a second to mentally prepare!”

“Oh, sorry. I got a little carried away there. Take your time, we don’t have to wake up early tomorrow so there’s plenty of time.”

Spike sat in Twilight’s bed, silently trying to build up the courage needed. It took him a few minutes to gather himself. He slapped himself hard on the cheeks with the palm of his claws, then slowly scooted up the bed a little more and opened up his legs, allowing better access to his privates. “...Ok. Let’s do it.”

Twilight chuckled. Even though Spike’s much taller than her now, she finds his nervousness quite cute. She’s glad he trusts her enough to have her guide him through his first time, and she didn’t want to disappoint. Her educator mode quickly kicked in. “So, as I was saying, the first thing we need to play with these toys is lube. It’s very important to make sure both you and the toy are well-lubricated. We don’t want any chafing or tears, those are painful.” She then gestured to his claws, “Do you want to try using your claws to stretch it out before we start with the toy? I think it would make things easier. Ponies don’t have that luxury since we have hooves instead of claws.”

Spike nodded. He reached for the bottle of lube and squeezed a big dollop of it onto his free claw, then reached for the vertical opening between his legs. His fingers moved clumsily as he tried to apply the lube liberally to the area, sticking them inside and trying his best to rub it all over. The lube is cold, and it felt pretty funny on his sensitive parts, but not in a bad way. He continued with his escapades for a little bit, slowly becoming more conscious of the act as he went. He moved one finger to two, then to three, gradually stretching out his insides in preparation for the toy’s grand entrance.

Twilight got out her notebook again, she planned to take all the notes she could. She observed a few drops of juice flowing out of his slit as he worked his fingers, forming a nice watery sheen in the area. She noted down that male dragons are capable of self-lubricating, and judging by the quiet moans escaping his maw, it’s starting to feel good.

“I think that’s good enough Spike, do you wanna move on?”

Spike nodded, sheepishly withdrawing his fingers. It’s pretty awkward doing something so private in front of others, made worse by the fact that it’s his first time, but he didn’t want to stop.

Twilight fetched the smaller toy from her nightstand, lathered lube all over it and handed it to Spike. It was in the shape of a griffin’s member but without the barbs. “This was my first toy, I really like the tapering on it. Should go in pretty easy, just remember to take it slow. Don’t push it if it hurts, okay?”

Spike carefully lined up the toy with his slit and rested the tip against it. He took a deep breath again, trying to mentally prepare himself for penetration. “This is it.” He thought, as he gave it a firm but gentle push.

The tip slowly slid inside him. It felt... firm, but also very soft, against the sensitive flesh of his penis inside, still flaccid. His body reacted to the foreign intrusion by tensing up involuntarily, but he continued to push the toy in with his left claw. His slit swallowed the toy up inch by inch. It made its way inside without much resistance or pain, thanks to his preparations and the copious amounts of lube used. Slowly but surely, the flared base of the red rocket made landfall against his scales. The toy really wasn’t that big, only three inches in length and barely thicker than two of his fingers, but it felt... full. Really full. It wasn’t unpleasant, though, the feeling of it resting against the underside of his penis inside was actually quite unique and pleasurable.

Spike gasped quietly as he bottomed out on the dildo, the tip poking at a sensitive bundle of nerve endings inside him. After a brief rest period, he resumed his endeavour. His left claw grabbed the base of the toy and slowly pulled at it, until only the tip remained inside him, then slowly pushed it back inside. The movement against his still soft member inside made him moan quietly. It was really embarrassing, he pulled a pillow over his face with his free claw, trying to muffle the involuntary noises he was making.

It smelled like Twilight. Well... it’s her pillow, and he’s in her room after all. But... he never noticed how... sweet, how... enticing... her scent was. Like a mixture of lavender and butterfly pea tea.

It was definitely weird at this point. Twilight’s like a big sister to him, he shouldn’t find her scent... sexy, but he did. Maybe it’s his arousal playing tricks on his mind, but Twilight’s scent was acting like an aphrodisiac to him at that moment. His left claw picked up its pace as he took a big sniff of her pillow, the act of which made Twilight blush as she observed his explorations.

Somehow Spike’s own dick remained soft through his increasing arousal, but it was becoming a lot more sensitive in the midst of getting rubbed and poked left and right by the erratic movement of the dildo inside him. His moan became louder as he worked the toy frantically, wanting to chase the next high. Juices were now overflowing between his legs and leaving a visible wet spot on Twilight’s sheets. He wanted more, more pleasure and more satisfaction.

Twilight closely observed the dragon pleasuring himself. It was an undoubtedly erotic sight, seeing him go at it with such urgency and intensity. She felt a tingle starting between her hind legs, but she tried to suppress it the best she could, continuing to document her observations.

Spike continued to thrust himself relentlessly with the smaller toy, but his insides were now fully stretched to its size and he felt the fullness fading away. It was no longer satisfying him. He wanted something bigger, something longer. He let the toy fall out of him as he reached for his original choice: a longer, thicker and more realistic-looking stallion-shaped dildo that he had thrown on the bed earlier. He didn’t properly lube the toy this time, he wasn’t thinking straight from being so turned on. The lack of lube and the bigger size made his clumsy insertion attempt a lot more difficult. He winced in pain as the flared tip popped into him.

Twilight had to step in before he could hurt himself further. Her horn lit up, and a purple aura appeared on the base of the dildo as she held it there, preventing Spike from pushing it any deeper inside himself. “Hey, Spike! Easy! Remember what we said earlier? Don’t be so impatient, you could really hurt yourself!”

Spike whined in frustration. He didn’t want to stop despite the pain. But Twilight’s words did knock some sense back into him. Begrudgingly, he pulled the tip out of himself as Twilight fetched the lube bottle and lathered on a thick layer of lube onto the toy. He knew his tendencies to go overboard when his desires would overwhelm him, and he felt he couldn’t trust himself fully knowing how horny he was. But he also didn’t want to stop here, he hadn’t climaxed yet, and he wanted more. A risky idea popped into his head, too embarrassing for him normally, but he was horny and common sense was scarce.

“Hey... Twi, Can you... maybe... help me with... that?”

Twilight stared at him, a little shocked and surprised at such a bold request. “Wait wait wait, so you're wanting me... to control this thing for you?”

“...Yeah. I... I can’t really think straight right now and I don’t think I can trust myself... You know how dragons get with greed, right? And right now I’m... I’m really greedy for... that cock to fill me up.” Spike recoiled into the bed as those words came out of him. He couldn’t believe what he just said.

That logic... actually made a lot of sense in Twilight’s head, but she couldn’t really get over the fact that this was Spike, who she viewed as her little brother, asking her to help him masturbate. It’s crossing basically all the lines and boundaries between a proper sibling relationship. There’s no way, right?

She took another look at the purple dragon now hiding behind two pillows. It was practically a dripping mess between those legs. He looked really, really desperate for some release, and she felt bad denying that from him.

And hey, in the end, this is all just for science... right?

So, despite her better judgment, she agreed, much to Spike’s delight.

“On one condition though, you have to tell me if I’m hurting you, okay?”

Spike gave her a meek nod.

Twilight turned her body to sit on the bed facing him. Her horn lit up again as the purple aura lighted up at the base of the long stallion dildo, but this time moving it into position between his legs. “Okay, relax now, and let me know when you’re ready.”

Spike sheepishly bent back both knees and opened up his legs, and moved both claws onto each side of his slit, pulling it open gently. It was quite the view, his member faintly visible inside, still appearing soft and pink. A faint blush appeared on Twilight’s cheeks but she tried to ignore that feeling and gently pushed the flared tip inside of him. Spike moaned out of pleasure. The lube made a big difference, this time it went in smoothly and with no pain at all.

Twilight continued the insertion, her eyes scanned his face intensely, watching for any grimacing. Slowly and gently inching the dildo deeper inside her number one assistant, who’s now squirming uncontrollably.

Spike was practically melting into the bed. The shaft inside him felt... incredibly huge, and it was putting a lot of pressure on his own sensitive dick, squeezing it against his own flesh and causing him intense pleasure. He can’t help but let out squeaks and squeals from his maw as the large stallion dildo made its way deeper inside him, panting intensely.

“Those are some cute noises you’re making there Spike.”

Twilight felt the need to tease him, just a little.

“Ha... Shut... Shut up! Oh...”

“Looks like you’re really enjoying yourself.”

“...Yeah... It’s... Ha. It’s really good... Keep going...”

The toy is long, about 10 inches, modelled after real pony junk. Unfortunately for Spike, his insides were not built to accommodate such lengths, only managing about two-thirds of the entire length, just past the ring, before bottoming out. Not that he cared, it felt incredibly full inside him, and the pressure against his own member was driving him into a frenzy of lust. His claws were grabbing onto Twilight’s sheets for dear life as she began slowly pumping that thing inside him, moaning loudly. The flare at the tip stretched him to his newbie limits and created a moving ring of intensity that slowly traversed up and down his body. “...Faster... Faster!” he called out, seeking that next level of euphoria.

Twilight watched as the purple dragon drifted deeper into the sea of pleasure, trying to keep her own calm. She can’t deny the scene in front of her was incredibly erotic, and her body reacted accordingly. The tingling between her own legs intensified as she observed him bobbing and weaving while she steadily increased the speed of her thrusts. This is not good, she thought. She was only observing for scientific reasons, and that was her little brother in front of her. She shouldn’t be aroused by him, but she couldn’t deny it as a small patch of wetness was now forming under the sheets where she was sitting. She tried distracting herself from those sinful urges, but only for them to hit her harder as Spike’s loud moans of pleasure shoved them back into her head. She couldn’t focus on the task at hand anymore, her thrusts becoming faster and more erratic.

“Ha... Wait... Twi... It’s, it’s... too much, ha... I think I’m really...!”

Spike couldn’t finish his sentence as the climax hit, causing the soft and squishy member inside his slit to explode. It felt like a huge wave washing over him, causing him to lose control of his limbs. He felt a strong need to hold something, something warm and soft and... sweet smelling. His instincts kicked in as he suddenly grabbed onto Twilight’s front hooves, pulled her down onto the bed, and hugged her, squeezing her tightly to his chest. The first wave washed over as a second wave inched in closer, crashing down on him, then a third, then a fourth, causing his own member to shoot squirts and squirts of dragon seed into his own insides, overflowing and wetting Twilight’s fur as he held her there. His maw was despite for something to chomp on as the climax continued. He bit her, on her shoulders, lightly, causing her to yelp in response. He held her close, arms wrapped around both her front legs, locking her in with her maw, and rode through the most intense climax he’d ever experienced.

The climax lasted over a minute, and as the final wave washed over him, it took away his strength. His arms relaxed around her as she was finally able to free herself from his grip. He slumped back onto the bed, exhausted, letting the large stallion toy fall out of him slowly. It took another minute for him to recover a little bit of his common sense. He glanced at Twilight, seeing the red bite mark on her shoulder, as a daunting realization set in.

“HOLY FUCK, I’M SO SORRY! I DIDN’T MEAN TO... I SWEAR! I... I DON’T KNOW WHAT CAME OVER ME...”

“It’s okay Spike. Your body... reacted more strongly than I anticipated.” She tried to comfort the frantic dragon, but she couldn’t really look at him right now, so she turned her back against him as she sat back up.

“But I... I hurt you! I didn’t mean to...”

“No, really, it’s fine. This didn’t hurt... well a little bit, but I’ll be fine... I just... didn’t anticipate you doing that, like, the whole hugging thing and all.”

“I’m really sorry, I’m...”

Spike scanned over Twilight’s body, looking for any more signs of damage, and that’s when he noticed the growing wet spot underneath her. Wait, it can’t be... He felt down his own body, onto his leg, the spot on his thigh that lined up against her crotch as he held her previously. It was wet.

“Wait... are you... wet?”

“It’s not like that! It’s... just a biological reaction!”

Twilight turned back, frantically trying to find any excuse for her own arousal. That’s when she noticed a rocket tip peeking out of his slit, and rapidly growing in size.

Spike pulled a blanket over himself trying to cover his now full-on hard-on. The both of them quickly turned their backs against each other in embarrassment.

“...I think I’m gonna go back to my own room now...”

“Yeah... I think that’s a good idea.”

Spike got off the bed and made his way to the exit, trying to hide his erect member from Twilight as best as he could.

“Sorry... for the mess, and... thank you, Twi.” He said, sheepishly, before closing the door behind him.

Twilight laid back down on her bed. She didn’t bother to clean up, she wasn’t in the mind space for that right now. The ball of fire inside her own body was simply too much at the moment.

She knew this was gonna be a long night to endure.

Author's Note

This is my first time writing a fic! I know the subject matter is a bit taboo (I mean who really ships Spike and Twi) but I like taboo crackships, so here ya go. I'm still quite inexperienced at this so any criticisms and suggestions are welcome!