(F to M Dog, F and M to F Horse)

“You know, I was hoping that the rent would be a little less…” Lisa looked at herself with a small smile, shaking her head. Her gorgeous figure was covered in shaggy white fluff thanks to her new costume.

“Less hot?” Her sister, Rebecca asked. Her voice was a little muffled, thanks to a cloth approximation of a horse’s head. Even through the mask, Lisa could hear the woman’s smile. “Not in that way, thermally.”

“Not quite…” Lisa looked to her backside. A cheap white tail brushed against her costume’s ankles, swaying with every wiggle of her hips. Luckily, the outfit was thick enough that she couldn’t feel its constant swaying.

“Less hot, but in the other way?” AJ asked from the doorway. He was the bottom half to his wife’s costume, a pair of suspenders keeping the horse’s comically large rump against his backside.

“Less embarrassing.” Lisa sighed. “I mean, I’m happy to help with chores, but since when is trick-or-treating a chore?”

“Since I wanted a pony, but ponies can’t exactly give out sweets.” Rebecca tutted.

“Yeah, about that… I don’t think Clydesdales count as ponies.” AJ kicked his feet, tilting his head at the swaying of the white pom-poms Rebecca had added to the outfit. “You sure the store’s not going to charge you for this?”

“Well, they won’t know. I’ll just pop the stitches out tomorrow.” Rebecca’s hands were on her hips, and Lisa had to bite back a laugh at how silly her sister looked.

Despite her best efforts, Lisa wasn’t fully able to keep herself from smiling.

“See, that’s the spirit,” AJ clapped her shoulder. “Just have fun with it.”

He was a little insufferable at times, but Lisa put up with him. After all, he made her sister happy, and her sister was the reason why she had a roof over her head. Still though, did she have to dress up like some kind of plus-sized furry?

“Hey, stop scrunching your nose like that,” said Rebecca. “You’re always welcome to trade with AJ.”

“And spend the whole night sucking your farts? I know you had barbecue last night.” Lisa scrunched her nose even more.

“Yeah, just the way Daddy likes it,” AJ laughed, then laughed harder at the disturbed look on Lisa’s face. “You’re really too easy. C’mon, zip us up.”

Lida grumbled to herself, but obliged… If only to shut him up.

However, as soon as the seam closed, she noticed something different in the air. It made her head feel a little funny, but in a good way. She wobbled in place, unaware of how the costumed pair before her were similarly swaying.

There was some part of her that had to wonder if there was a gas leak, or if she’d somehow mixed up one of the Halloween treats with some of AJ’s special gummies. But the latter always made her paranoid, and the former… Well, it had been a few years since she’d had gummy snacks, but had they ever been THAT good?

More to the point, there was something weird about her body. It was like she was getting worked up, but in a new way. She was used to an ache, a desperate emptiness that had to be filled no matter what.

This was warmer, more… Driven. An urge to press herself against something and… Really enjoy it? She wasn’t quite sure.

Despite herself, Lisa pressed herself against the horse rump in front of her. To her surprise, it was oddly warm and fleshy. She gave it an experimental squeeze and heard a muffled sound from within the costume.

“What’s the matter? I thought you like this,” Lisa huffed with amusement at AJ’s evident discomfort. Something about how he was moving seemed wrong, though. Plus the muffled sounds he was making made something distant flicker in her brain.

“Hey… You okay?” Lisa leaned forward, pressing her hands against roughly where she thought AJ’s head would be. As she did, she noticed how swollen her hands looked.

Actually, now that she thought about it, her face felt pretty swollen too. Lisa crinkled her nose, wondering if she could always see so much of it. And if it was always so black. Maybe she’d put makeup on it earlier? She couldn’t quite tell.

What she could tell; however, was that the costume beneath her seemed to be expanding and contracting… Almost like it was breathing.

“L-Lisa? I think something’s wrong…” Rebecca’s voice came from within the stuffed horse’s head. The words were said with enough force to jiggle the mask slightly.

They also sounded… Pretty. Lisa panted hotly, rolling her head from side to side, feeling her ears warmly brush against her cheeks. That felt wrong too. Maybe it was because she thought they should be softer?

Lisa couldn’t help herself from bumping her hips against AJ’s. It made a shiver of pleasure run through her, and her eyes rolled. She rubbed against him a little more. She sucked in deeper breaths, letting her chest rise and fall.

Her hind paws left the ground, and Lisa finally realized something was wrong. Feet. They were supposed to be feet, weren’t they? But she was sure they felt like paws.

She kicked her legs, thumping them against the backs of AJ’s legs. How long had she been grinding against him for? Was she really humping him?

“a-LuhEEEsuh!”

How long had Rebecca been calling her name? And… Was Rebecca always able to move that horse mouth like that?

Lisa struggled to focus, taking in the details of what she was seeing. It looked like the horse’s mask was staring right at her. Then it blinked, and Lisa near fell off her back.

One thing in particular kept them tethered, one amazingly pleasurable thing that Lisa now realized was well inside AJ.

If… There even was an AJ. Lisa became keenly aware that the only thing she could hear was Rebecca’s panicked gasps – or was it pleasure? Curiously, Lisa pumped her… His hips, and earned a whinny in reply.

A part of her realized this was wrong.  This shouldn’t be happening. She was somehow deep inside her sister’s husband’s… Oh. AJ definitely wasn’t supposed to have one of those. But damn, did it feel good.

Too good. A part of her realized this war wrong, but most of him too good to care about anything but feeling more pleasure. He pumped his hips again, tongue lolling from his mouth. He licked away the last of his old lipstick, revealing dark, rubbery lips beneath.

The horse struggled to choke out words, even as her treacherous hindquarters clenched around Lisa. Lisa barely noticed, too driven to keep pumping her hips, even as the horse’s grew larger, lifting him further off the ground.

He clamped his paws onto her hips, earning another pleasure-stricken whinny from the horse. He humped harder, slobbered onto her back, did everything a dog like him was supposed to. And she soon replied in kind, nothing but a desperate mare.