Already you could tell there was something peculiar about the dildo you had ordered. Sure, it was modelled after a horse cock, but that wasn't what was unusual about it. No, what struck you was the aura that it had, one that tickled something deep and e̶q̶u̶i̶n̶e̶ primal within you. From its length to its girth, and even its smell- not the plasticky scent of silicon but more earthy and musty, more natural. The urge grew, you needed this thing planted within you, now.

So you lay yourself out on the floor, taking the base of the cock in a hand, ready to press it inside. But, you find your aim compelled elsewhere- not towards your anus, despite how ready it was, but instead towards your sack. Had you another moment to ponder this, perhaps you would have shifted your aim. But, in your excitement, you push it down, and the tip strikes against your jewels.

There was the all too familiar sickening lurch of your nethers and gut, having your nuts struck like that, but you were committed, for reasons god knows why. You pull back, and strike again. Another lurch, one that threatens to send your lunch up your throat and across your face... But the tip of the dildo was striking... deeper. You wanted more. So again you pull back, and again you push, and this time- oh, what a wonderful feeling, as if you were opening up, both physically and spiritually. The wave of nausea was fading away, instead replaced by a tightness in your sack, one that was pulling on each testes, as if to escape from your abuse. And you know... that wasn't a bad idea- why not help them along?

Again you strike, pushing the tip deeper inside of you, forcing your balls to foist themselves tight against your crotch, as if it were a cold winter night. But it was anything but cold- you were red hot, and down to get hotter, as you twist and work the tip into the crevice that was forming where your balls once say. More. Just a bit more. Back... then in.
A gasp, one higher and softer than you expected, escapes from your lips as one part of your sex slips inside, squeezing and turning through canals that your body had long considered closed. Another strike, another gasp, and the other goes a similar way, a pleasant warmth radiating from below your belly as they nestle into a more familiar place, one that seems more intimate and true.

The tip was further within you now, and there was no turning back- Not like you wanted to, anyway. The median ring was so close to coming inside- you wanted it. You wanted to draw out every last piece of masculinity from you, leave you as a gasping and moaning little mare. To let its masculinity overwhelm and consume your own. To let it blossom forth within you and give you the opportunity to be the mother you found that you wanted to be. Your own shaft quivered, as if afraid, dribbling out a milky and thinning seed that you no longer found any use for. But you weren't afraid.

You right yourself, putting yourself into a squat, and letting the base of your stallion rest firmly against the floor. Bit by bit, you lower yourself, letting out a moan as you let him carve his way into you, splitting open flesh that was meant to be open, that was meant to be filled. Your cock withdrew, retreating from a losing battle as it dribbled out the last load it would ever release. Just as you reached the median ring, your old self asserted its new identity as a clit,  slipping into the thickening lips of your gash right as you slip over the ring.

Whatever a wonderful feeling that was, leaving you laughing, crying, and sweating, rocking on hindhooves you didn't even realize you grew, scraping the floor with forehooves you couldn't wait to trot with. You were a mare, and you were happy with that.
You settle your weight down completely onto your haunches, letting your stallion completely inside of you. Something below your belly churns, a heat and pressure that made you tremble. You press your hooves against your belly, as if to contain the feeling that almost wanted to pop out of you. You knew what it was, it didn't have to be said. Just the final step... Just the final step until...

Your stallion fidgeted, and a warmth flows inside of you. It was enough to pull you out of your reverie, shouting in surprise as you leapt off the dildo and landed on all four hooves. How... What... How could it have...?

And yet, you can see the dildo sitting there, a fresh load of cum running down its length... With the moment suddenly interrupted, you were left there to consider how you now stood on four hooves, your ears pinning against your neck, and a tail swaying from your rear. For a moment, terror and fear threatened to grip you... until you realized once more the warmth coming from under your belly. It gave you some assurance. Some comfort. A feeling that everything would be alright. That you were going to be a wonderful mother, to a beautiful little foal.

Another shining light brought to the world.