It wasn't long before the two found themselves wandering a little way past the animal costume section, into a section a bit more adult version of the animal section that was out of the view of the public, with costumes that had more pronounced sexual features.
There was one costume that seemed a little out of place, it looked like a regular two person horse costume, sleek and black as midnight, until they realized it was missing a head. Katie took a close look at the instructions attached to the hanger, and showed John one of the images that showed a woman in the front section being penetrated by the man in the hind section, as if doing it reverse cowgirl style.
The two giggled, it didn't seem a particularly practical to wear it like that; since the man would have to fill the hind legs with his arms, but it seemed like something fun to wear for a one time night of fun.
It wasn't long before the two were ringing it up the cashier giving an impish smile to imply she understood what the two planned to do with it, even as the two blushed silently themselves and shuffled out.
---
The two had gotten home to try the centaur costume on, and found that the costume had supports to keep it supported and upright while both were in the costume, so once Katie entered the front part and strapped on a harness, the thing would easily hold up John.
"Alright, you're up darling," Katie said.
Getting on top of the costume so that he could slide in was a lot like trying to mount a horse, but it was easier than expected as he soon slid his legs in between Katie's, allowing him to push his arms out behind himself to slide them into the hind legs. With his face managing to fit into some cavity between the round girly butt of the horse section.
Katie had to push his head back so that she could zip the costume up over him, causing his mouth to slip in a rubbery tube from what must have been the fake vulva in the back of the costume, likely so whoever was in the back could suck off people mounting the costume.
It wasn't long until Katie had finished zipping up the costume, the costume creating a comfortable seal around the both of them; leaving Katie with only a headband with hard furred horse ears and a pair of backwards pointing horns to place on her head, having found it in side the costume while setting it up. It snapped into place before Katie could even adjust it, yet it seemed to be perfectly fitted where it ended up.
The two slid back and forth, trying to angle it so that John's dick would slide into her; and the first couple of times it missed, but then the costume seemed to constrict around them. Katie found it quite pleasurable, as the edges of the costume squeezing against her felt like soothing gel, and soon the two felt their sexes right up against each other, being squeezed even as John's dick got harder, leaving it only one place to go as John's dick speared Katie's pussy; only for bucking for pleasure to get harder, as there was no room for them to separate for proper thrusting.
John meanwhile as Katie bucked back and forth felt the ass cavity of the costume get pulled tight into his face; if it wasn't for the little bit of pussy hole, he might have been suffocated by the costume compressing all the air out of itself. He got a little worried as he felt gel leaking onto his teeth, it feeling like his teeth was being glued to the vaginal opening; not to mention, with how light the hind legs of the costume were getting, it almost felt like his hands were melting into the gel lining.
The two's worries dissipated as both were suddenly thrust into climax, their vision practically whiting out as their entire body tingled. Katie herself felt like she was having an out of body experience as if she was becoming one with the costume, while John felt like his body was exploding into a river of molten energy flowing in and out of Katie, only contained by the costume between them.
If either had more presence of mind, they may have seen a swirling aura around them as the magic of the costume bound the two into their new form.
John couldn't help but swish the tail as he tried to fan off the sweat and animalistic heat pouring from his lips. Part of him registered that he had been twisted into a mare body, but the afterglow of pleasure made him almost happy about this, like being stuck with his centre of consciousness nestled inside a mare pussy was some bizarre kind of bondage; his, or perhaps her, vaginal lips leaking with the combined arousal of the two of them.
Katie herself was practically brought to her knees as it were, making it look like the two of them were presenting. "Are you alright back there?" Katie said, feeling her body continuing out behind her.
'I'm okay' a voice in her mind seemed to call out. 'This is... Kind of kinky'.
Kattie kind of giggled, and with her presence of mind, grasped at the costume instructions; a brief flip through didn't seem to provide any information on removing it. "We might be stuck," Katie said, "the instructions don't say anything after how to put it on."
John winked her vulva in some weird masochistic excitement. 'I... I think that's actually kind of exciting, in a messed up way.'
Katie laughed. "What, getting excited about horse cock all of a sudden, given that's what you'd be taking like that," Katie said, only for images of young horny girls rubbing their pussies against John's new rump face to invade her mind, "huh... Then again, maybe the costume has turned us both... Bi I guess."
John's heat intensified for a brief moment as if blushing, as she rubbed her flanks together like she was trying to hold in her excitement. '...Maybe? I mean... Both certainly sounds nice.'
Katie smiled, and looked around; her room, now their room, seemed to have gotten bigger after their climax. And she found herself pulling the two towards a wardrobe, her control of the forelegs guiding them. As she opened it, she quickly pulled out a soft pink set of lingerie to look at it, noting it had four pieces rather than two.
As Katie started running her down her belly, she eventually caught on something sensitive, which caused John's consciousness to seem to spin around like he was turning his head; and we found himself looking out at Katie's hand through a vagina nested between their forelegs, causing John to raise on of said forelegs they both seemed to control as if by reflex.
Katie did feel John's sudden perspective switch, and removed her hand to show John their new clothes. "Looks like we're going to need a pair of panties on each end," she said, showing both a pair of panties with what looked like the back cut out, and a pair with a tail hole, though the latter pair seemed distorted, as the front was kind of shortened, while the back was extended, perhaps to account for the bent over stance.
John adjusted her stance as she caught a glimpse of a mirror, and looking at herself, standing front on, they could easily be mistaken for some kind of satyr, aside from having forelegs instead of hind legs. Their dark lower half a stark contrast to the upper, save for the pink bit of slit poking out between the legs. Taking a little spin, they noted the lower half was closer to the size of a pony than a full horse,
Turning to their rear end with John's perspective returning to the sex back there on the way, John got a good look at a slit not quite as equine as expected; certainly positioned like a horse, but much slimmer and tighter, parting her lips a bit with a wink, she figured it might actually be fairly tight even by human standards, so she might not have to worry about only horse dicks being able to satisfy her; appropriate, given her ass was round and firm like a human girl's ass rather than the thick trunks of a realistic pony. John then drew her attention lower, with something swinging between her legs which she parted, finding two black furred breasts swinging just bellow her right in front of her legs in lieu of a proper udder.
Katie was looking over her shoulder as John looked in the mirror. "Huh, so that's what the other bra was for," she said. She turned over the four piece set of lingerie, and noted that the set for her horse boobs seemed to have the shoulder straps attach to the panties; though perhaps another set wound just have the straps go between their legs and over their crotch to either side of the vulva in place of the shoulders.
'Funny that we need to cover up the horse bits too,' John thought.
Katie laughed. "Who's to say its not just to show off? We haven't looked at the rest of our new clothes yet, just the fun bits," Katie said, "though, maybe you'd like us to go out; dress up, show off a little and bring home a few boys and girls to fuck us every which way... Or maybe dress up just for ourselves, I'm sure that would be fun... Unless you just want to skip straight to stuffing ourselves full with whatever toys we can dig out."
John's arousal dripped down onto the carpet as Katie brought up these ideas, each of which excited her at both ends.