It’s a pleasant spring Saturday in Canterlot, the afternoon sun gently shines down upon the capital of Equestria, bringing a loving warmth befitting the celestial body controlled by Equestira’s motherly princess. That golden sun gently filters through the windows of Canterlot Castle bringing a little of the solar princess’s warmth to the quiet halls of the castle. The staff worked extra hard to finish all of their work before lunch so they could get out and enjoy the day.
The absence of ponies meant there was no one around to hear the lurid moans and groans of a pair of ponies fucking each other’s brains out. Their moans reach a crescendo with their bodies that absolutely would have been heard by anyone, were they in the area. Soon though things quiet down, as Dusk Shine pulls out of his sister, Gleaming Shield and pulls her onto his chest as he lays back against a big pile of pillows at the head of the bed.
The two of them lay there, resting after their sexual escapade, Dusk gently playing with Gleaming’s mane while she rests her head on his shoulder. Despite the fact that Gleaming is still physically bigger than Dusk, he holds her like she’s the smaller sibling. The two of them lay there for a while before Dusk speaks up.
“It's been a while since we've had a chance to do this, BSBFF.” Dusk says as he twirls her mane with his hoof.
“Too long, that’s for sure.” Gleaming says with a sigh. “And you’ve gotten better too.”
“Of course, I’m a grown stallion, Gleaming. I’ve had a chance to practice with a couple of friends with benefits.” He says as he pats her head.
“You’ve certainly grown a lot.” Gleaming leans into the patting for a moment before using her magic to ruffle his mane.
“I should really take the role of the older sibling now that I’m an adult.” Dusk ruffles his sister’s mane for a moment before nibbling on her ear.
The nibbling gets a squeak from Gleaming who blushes, laughs and pulls away from him a little. “Honestly Shine, you’re still too immature to really be the older sibling. Sure, you’ve come a long way since you were the curious little colt who asked if we could “commit coitus,” but you’ve still got a ways to go to take that role.”
“I’m being serious, Gleaming.” Dusk replies with a cross expression.
“As am I, Shine.” Gleaming’s laughter dies down as she looks him in the eye. “Plus, you’re still smaller than me.”
“You know I could change that, Gleaming.” Dusk says as Gleaming rolls off of him and climbs off of the bed.
Gleaming laughs as she starts towards the bathroom, “Sure you could, sure you could.”
Dusk Shine grinds his teeth for a moment before his horn lights up with a powerful flash of magic that quickly grows stronger, gaining a layer of over-glow as he rises from the bed. Dusk trains his horn on Gleaming and hits her square in the back with the spell. The spell takes hold of Gleamings body and quickly shrinks her down to the size of a school filly roughly the age of the Crusaders.
Gleaming yelps as the spell hits her, stumbling mid-step as the world suddenly gets significantly bigger around her. The doorknob that was once chest height now sits a good head taller than her and the door looks almost monolithic. She tries to quickly turn around to confront her brother, but ends up stumbling thanks to her new size. When she turns around to face her brother it becomes clear just how much smaller she is than him.
“Dusk! Why’d you do that?!” Gleaming practically squeaks out, her voice several octaves higher than it was before.
“Heh, I wanted to see how you’d look as a filly. Also, now that you look the part you should really act like the younger sibling.” Dusk says as he walks over to her and ruffles her hair, only to have her stab at him with her horn. “The spell is temporary.”
“Change me back!” Gleaming squeaks and stomps her hooves a bit.
“You’ll change back on your own, unless you orgasm while you’re that size, then you’ll have to grow up the old fashion way again.” Dusk says as he licks his lips and leers lustfully at her.
“You’re not going to try and make me orgasm.” Gleaming says as she takes a couple of steps back. “You’re not going to try to make me orgasm, right?”
Dusk takes a step towards Gleaming and that’s all the motivation she needs to start running. Despite her new size she’s quick, her little hooves carry her out of the bedroom and into the main room of the suite before Dusk can react. Her magic tosses the door to the suite open so she can run out into the hall. By this point Dusk’s had a chance to start moving too, and thanks to his bigger legs he’s able to move further with each step.
As Gleaming sprints down the hall, Dusk bursts out of the room and charges after her. His bigger size lets him catch up to her very quickly and tackle her to the ground with ease. Gleaming lets out a scream as he slams her to the ground, not expecting him to actually be able to catch her. She flails under Dusk’s weight but her hooves hit uselessly against him, which gets a chuckle out of him.
Dusk smiles lecherously down as his much smaller sister as he grabs her flailing hooves and holds them down on the ground. Gleaming glares up at him and continues to struggle, trying to escape but failing.
“Look at how small you are compared to me, Gleaming.” Dusk says as he adjusts his position to allow his hardening cock to rub against one of her hind legs. “Now you really are my little sister.”
“Stop it Dusk, I don’t want to be stuck at this size again!” Gleaming shouts up at him as she tries to charge her horn and shove him off, only to find that her magic refuses to respond.
“Oh, I forgot to mention, this spell also regresses your magic wellspring too. If you keep trying to use your magic you’ll end up passing out and that won’t be fun for either of us.” Dusk smirks before leaning in and licking her horn. “Accept your place, Gleaming.”
“N-no, I won’t.” Gleaming whimpers as Dusk goes from licking her horn to sucking on it for a moment. The sensation completely disrupts her attempts to access her magic and makes her start to leak a little down there.
“Then I’m going to have to make you stay like this.” Dusk grinds his dick against the inside of her left hind leg, his cock already mostly erect.
“Stop it Dusk!” Gleaming whines, struggling a bit again as Dusk makes his intentions very clear.
Dusk’s horn lights up, his magic helping to hold Gleaming in place as he adjusts himself properly. His rock hard pecker pokes her pussy, making her shout again, this time calling for help. Dusk simply smirks and pushes his shaft into her very tight filly cunt, the size of his dick spreading her somewhat painfully as he slowly pushes the first couple inches into her. Gleaming whimpers and cries under him from the pain of her small fillyhood being spread over the girth of his adult sized penis.
Dusk holds himself there, letting his little sister adapt to the size of his cock for a few moments before slowly pressing further in. As his dick slips into her depths it causes her belly to visibly bulge, eventually he’s stopped by her cervix with just about half his cock inside of her. He gives her a couple of moments to adjust before he starts thrusting, each pull and push makes Gleaming’s body shiver and twitch under him. She continues to try and stop him, but her efforts are hampered by his gentle thrusts and a slowly building desire inside of her.
Gleaming whimpers as Dusk dominates her in the middle of the hallway. Despite her efforts to resist her brother’s forceful advances, his size is simply too much for her to overcome at this size. The initial pain of his cock stretching him quickly faded and was replaced with a strange warmth and pleasure that she didn’t want.
Now, as Dusk slowly fucks her, she’s fighting a loosing battle against her body. The familiar feeling of being in heat seeps into her body, the desire to breed and the need to orgasm warring against her desire to not be stuck as a filly again. All the while Dusk stares down at her with an insufferable grin as his cock grinds against several sensitive spots inside of her love tunnel with each thrust.
Slowly Dusk’s actions push Gleaming up to the brink of orgasm and then over it. Gleaming lets out a powerful moan as she climaxes, her body wracked with both her orgasm and the magic of the spell solidifying her fate as the smaller—and younger—sibling. Dusk simply smirks down at her and continues to thrust slowly as her young pussy milks his cock to the best of its ability.
Once Gleaming’s orgasm comes to an end Dusk picks up his pace a little, his hooves still holding her down by the legs as he thrusts his big dick into her small body. Having her filly juices coating his cock makes it easier to fuck her, the slick sex fluids letting him thrust into her quicker and a little deeper as his cock twitches and spurts little dollops of pre-cum.
Rutting her in the middle of the hall where somepony could walk in on them at any moment simply adds to Dusk’s lust. All of a sudden, as he adjusts his hips and thrusts into her again, she moans and climaxes again, soaking their crotches with even more of her filly cum.
“Looks like you really are the little sister now, Gleaming.” He grunts as he drives his cock into her depths again.
Gleaming can’t reply as she pants and rides out the high of her second climax. Even as her eyes roll back into her head from the power of her climax, Dusk’s form dominates her vision. She simply can’t escape him as he thrusts into her depths throughout her orgasm. His overpowering strength kept her held down, firmly pressed into the floor of the hall.
Dusk continues fucking his little sister, slowly slightly to stave off his own orgasm qs he savors the feeling of her tight cunt around his cock. Dusk smiles down at her, fucking her like this is everything he dreamed of. Being the bigger of the two makes it so much easier to fill every inch of her with his cock. Having her belly bulge with each thrust was also an erotic bonus of her new size.
At this point Gleaming can only pant and moan between gasping breaths, her body having lost all ability to fight back. With the warm stirring of heat, the two orgasms and her new size, what would have been mildly exhausting before, now has her utterly unable to do anything. As she lays there under her big brother a feeling of shame wells within her, shame that she couldn't resist Dusk, shame that she came so quickly, shame that somewhere deep down, she likes it.
Those thoughts are suppressed as she has a third orgasm, her body not really producing much in the way of filly cum this time. Gleaming's moans are also quieter, the exertion of multiple orgasms having worn her out a fair bit. Her fillyhood weakly squeezes Dusk's shaft which still makes him thrust a bit faster.
Dusk's ability to hold back his own orgasm starts to crumble as she milks him softly with her third orgasm. He picks up his pace as his dick throbs inside of her, his flare starting to expand. A couple dozen more thrusts and Dusk's cock is fully flared as he hits his peak. His shaft pulses powerfully with each spurt of cum as he packs her womb full of his seed, her belly swelling slightly from the size of his load. His load is big enough that it eventually forces its way out around his cock, dribbling down Gleaming's crotch and onto her tail and the floor.
Gleaming looks away shamefully as her body milks his cock, the waves of warmth filling her sealing her fate even more than her first orgasm. She can't say anything with how tired and out of breath she is, not that she'd really know what to say. As Dusk's orgasm comes to an end, he pulls out of her and off of her. Despite the freedom, Gleaming doesn't move, not caring to try as more of his cum leaks out of her and onto her tail.
Dusk uses his magic to lift her onto his back, casting a quick glance at the mess and deciding to leave it for one of the maids as he carries her back to her room. Her filly cunt leaks his spunk onto his back during the walk so their first destination is the bathroom for a proper bath.
It takes a bit of time for the bath to fill with warm water, but when it's ready, Dusk climbs in with Gleaming in his magic and sets to work cleaning the two of them up. The bath lasts for about half an hour but by the end of it the two of them are clean as a whistle. Dusk takes his time to gently dry Gleaming before bringing her over to the bed and wrapping her in a big snuggly hug.
"I promise I'll take care of your needs, just like a big brother should." Dusk says to Gleaming as she drifts off to sleep, exhaustion catching up with her at last.
With his sister held in his forelegs, Dusk also decides it's a good time for a nap, slowly and carefully adjusting until he's comfy in bed without waking Gleaming, before he drifts off to sleep.