Fandom: Steven Universe. Story idea: Fusions live in a rift space when their component gems are not fused, and the rift space is in a near constant state of orgy. Contains: Yuri, oral, tribbing.
"Woah.. where.. where am I?" Smokey Quartz questioned as she looked around at the void of colors around her. "You're in the Fusion Space," A tall, long haired fusion with a figure that made Smokey blush said as she approached, "This is where all us fusions spend our time when we aren't being formed out in the real world. My name's Rainbow Quartz."
"Smokey." She introduced herself, looking around, "Are we the only ones here or..?" "On no, not at all, but the others moved away from the spot where new fusions pop in so as not to..overwhelm them." Rainbow explained. "Overwhelmed? Me? I can handle anything." Smokey declared. Rainbow giggled, "Remember you said that. Follow me."
Rainbow quartz led Smokey across the colorful void of space to where all the other fusions were, "Now, we don't spend all of our time here, but this is where we spend the most time when not in use." Rainbow said, pointing to the massive fusion orgy. Sugilite had shapeshifted a futa cock and was brutally fucking Opal into the ground while nearby Sardonyx, shapeshifted into a smaller form, lay in a sixty-nine with Stevonnie.
Malachite and Alexandrite appeared to be in some kind of aggressive hate fuck, both struggling for dominance over the other. The tabled were turned when the corrupted Jasper fusion joined them, and the two began to gang up on Alexandrite; not that she actually seemed to care all that much.
"So fusions just fuck all day?" Smokey questioned. "Of course not," Rainbow said, "We've got entire lives in here. But without much else to do, we spend a lot of time here, having fun together. So, still think you can handle anything~?"
Rainbow Quartz was teasing of course. She didn't actually expect Smokey to join the party now or anytime soon. It had taken Stevonnie months to finally try it out. To her surprise though, Smokey seemed to take the teasing as a challenge. She grabbed the curvy fusion and pulled her down into a kiss, pushing her tongue inside of her mouth dominantly, "Anything, any time." She stated again.
Rainbow quartz grinned, letting her clothes vanish into light off of her body, leaving her naked, "Let's see it then~" Blushing against, Smokey only hesitated a moment before shifting her clothes off. Her chest was actually bigger than Rainbow's, if only slightly. She was female by default, as the fusion focused more on Steven's gem biology than his human parts, but if she wanted she could have shapeshifted into a futa easily, or even a D-girl, which no other fusion save for perhaps Stevonnie could do.
Rainbow got down and asked Smokey to get on her back. The three armed fusion did so, and Rainbow held her legs apart, plunging her tongue, highly skilled from decades of practice with the other fusions, into her pussy. Smokey groaned immediately, gripping the ground with all three hands as her hips reflexively bucked against Rainbow Quartz's face.
Rainbow found this cute, and pushed her tongue even deeper, wanting to see how quickly she could make the shorter fusion cum. As it happened, Smokey only lasted about five minutes before she came with a cry of pleasure, drenching Rainbow in earthy tasting juices. She licked her lips and moved forward, interlocking her legs with Smokey's so their pussies were pressed together.
She held Smokey down and began grinding their hips together. Smokey moaned, holding onto Rainbow as she thrust her hips smack wet slits together harder and faster. Smokey began to mimic the motions, grinding herself against Rainbow and causing them both to moan louder as they kept going, both getting more and more pleasure from it.
Smokey lasted a little longer this time, going ten minutes before she came again. Rainbow, close but not finished, moved forward and straddled Smokey's face. Smokey, believing she understood, pushed her tongue inside, shapeshifting it in that way only Amethyst and her fusions could to get it deep inside of Rainbow, pushing her over the edge as well.
Smokey lapped up the sweet tasting juices that flowed out as Rainbow came, and the taller fusion stood, "Oh you're going to fit in here wonderfully~"
Potential for this story is actually better than it appears at first glance. It could be just a massive one shot showing multiple different fusion pairings, or it could be a story showing the lives, relationships, and sexy times of the different fusions in this world where they all exist at once. I could even delve into as of yet unseen fusions.