When you had become a teenage drake, you were glad that your height wasn't the only thing to grow. Mind you, your cock would grow on its own from time to time, but it would shrink back down after a while. Now, however, it's at a length that you can be proud of.
The fact it's on Twilight's crotch makes you slightly less proud.
"It worked!" she says behind you, your knees kneeling on the mattress of her bed. She looking down at your once scaly dick, dangling between her legs. She then looks up. "You ready to begin the experiment? Your thingy may be on me, but you'll be the one to feel all the sensations."
You raise an eyebrow. How did you agree to this again?
"So it's going to feel like I'm putting my dick in someone else," you say in a tone of uncertainty, "but it's also going to feel like someone is ramming my dick up my ass?"
"Precisely," Twilight says, and you feel the mattress shift, accommodating the new weight. You gulp. "If I were to get anything out of this, then I wouldn't be able to be objective; if you weren't getting anything, then you wouldn't be doing this."
Oh, right. Twilight had offered you anal: she just didn't tell you who's.
"Now that we're done talking," Twilight says, and you feel something prod at your ass. You can feel your dick flare in suspense and your asshole open and close in fear. "It's time to begin fucking!"
How is it Twilight can make the dirtiest, messed up act, sound so innocent? It's as if she truly just curious about the results of this weird exchange without considering the connotations attached to it. For a moment, you consider the possibility of her having Asperger, and then you feel your cock enter your ass.
It's both the greatest and awful sensation you've ever felt.
You feel your cock slide into the tight tunnel, the walls lucubrating the length of your shaft, clenching on it out of pure reflex—and it feels fucking fantastic. Your ass, however, is crying out pain at feeling a foreign object inside it for the first time, feeling so wrong as something that's not supposed to be in your tunnel is now pushing against its walls.
You're both happy and sad when Twilight pulls out.
"How was that for your first taste?" she says. You give her your answer, and then she gives you a hopeful expression. "I'd be concerned if you enjoyed it outright—no pony enjoys having a cock up their ass for the first time."
It's that innocent tone again. How does she do it?!
"Now then." You feel the bed move as she shifts, the fur of two hands placing themselves on your butt cheeks. "Time to make you feel good in both ways!" She parts your cheeks like that one guy did the red sea, ramming your dick back up your ass, and you yelp once more. "There we go!"
No creature should ever be capable of such innocent. And no creature should ever be turned on by such innocence. Your cock stretches further down your tunnel, much to your chagrin, in more ways than just one.
"Now Spike," you hear the voice beyond your shoulders, slightly panting. "I want you to focus on how it feels to have it inside you instead of the sensation of your dick. Can you do that?"
You try. These findings are important to her, in some fucked up innocent way, and you could never call yourself a true number-one assistant if you did not comply with her requests. You focus on the sensation of your ass, which feels so alien to your mind, being in a state its never been in before—but you bypass the strange effect.
You focus on the walls of your anal, never really ever considering their existence before until something hard is pressing against it. You have to admit, that despite the strangeness, the feeling of their existence isn't unpleasant. In fact, the more you focus on it, the more you're able to derive pleasure from it.
"It feels kinda nice," you say, shakily. "No doubt it's weird, but if you get past the weirdness, it feels kinda nice to have something filling out back there."
"Now aren't you the good boy?" she says, patting the spines atop your head. "Now that you're over yourself, it's time to move on to stage two!"
You feel your cock dive forward, it delighting in fully being accommodating inside your tunnel, which clenches down on every inch of it. You yelp in surprise, but its pitch is filled with that as pleasure, your walls feeling so deviously good at being prodded, of being pushed outward, that the sensation makes your cock even harder.
The absurdity of the situation turns out to be the greatest joy in of itself.
"How does it feel, Spike?" There's a shift in Twilight's voice, one of that of an interested authority, her breath upon your ear-fins. "Knowing that your cock is on my crotch, fucking your own ass? That you're getting off on the dirty sensation of fucking yourself?"
She whines, pulling out till your tip is the only thing past your asshole, before ramming it back in, again and again. "That your dear sister is doing all the hard work, just to make you cum? You better intake every sensation and describe it vividly."
You feel great and fucking better than that. Your cock is ramming up the tight tunnel, over and over, that it's like your having sex with the tightest pussy around. Your ass, however, carries the sensation of said pussy—of being split apart and of being filled. The sensation of your walls accommodating the shaft, of feeling it rub all along them, pushing them outward as they contract inward.
So, in short, you were getting the full package deal. You really did owe Twilight after this.
"Did you know that the pleasure spots for males is actually in their ass?" Twilight says, beginning to ram you faster than before. "To think that some males will enjoy that bliss due to stigma, even fewer to do so with their own cock, and intake every sensation. You were quite easy to break in—you should be proud of yourself for being so open-minded.
Pride is the last thing on your mind as you feel a pressure building at the base of your shaft. Twilight's thighs are slamming against your ass as she gets into a groove, the fur of her coat nice on your rear, her stomach periodically resting along your back, and her forehooves dangling over your shoulder. The sensation of her marely body on your own feels good, quelling the feeling that any of this could be considered gay.
"Oh, is time to finish up so soon?" she says, her hindlegs adjusting on the matters. She begins to thrust at the fastest speed possible. "Guess all good boys deserve to finish."
You can't take the building sensation still anymore, banging your ass against your cock to acquire even more of the sensation, the act going on for a few moments longer. You pant, your cock filling your ass, which clenches more and more, until you blow over, filling yourself with your own seed.
You then fall forward in exhaustion.
"Interesting," Twilight says, hopping from the bed, and turning to gaze at your collapsed form. With the glow of her horn, magic of the same color surrounds her crotch, removing that which is not hers and returning it to its true owner.
Oh, and seamen is leaking out your asshole BTW.
"Now that is over with." Twilight levitates a clipboard out from nowhere and holds it before her face, peering at you from over its top. "I want you to describe the act in every way possible."
You regale the experience, hinting that she may have also turned you gay.
