Admittedly running out of ideas on this one...but then I came up with something. Heheheheheheheh.
Steven watches in fear as Jasper walks in, already nude. "Alright, cub, ready for your last lesson?" The young boy nods slowly, swallowing hard in fear. "So far you've seen how the female form can be used to give you pleasure. But now, I'm here to show you something special. On your hands and knees, boy."
He obeys submissively, flinching when Jasper grunts. "Other way." He turns around slowly, facing away from the warrior and waiting in fear. When he starts to look back, he sees an odd sight...an incredibly long tongue. Surprised, he goes to ask a question but cuts off with a gasp, fisting the blankets below him.
[She put it up my-] He groans again as the moist tendril presses further into him. At first, the sensation is weird, but as he gets used to it and relaxes, he can feel it start to feel better. [It's...not that bad,] he admits. He looks down between his legs to see he'd recovered faster than before.
As suddenly as it started, Jasper removed her tongue, and Steven looks back in confusion. "Oh, it's not over, cub. That was just the first part. Turn back around." He obeys, looking back at the wall and waiting.
Suddenly, something much firmer presses against him from behind. As it breaks past the ring of his anus, he figures out what it is. [A...finger?] He grunts as the firmer digit thrusts in and out, not too painful but certainly a tad uncomfortable. "Th-that feels w-weird," he complains, causing the warrior to stop.
"That's why I'm building you up to it. Now quiet, you're almost loose enough." Steven swallows hard, suddenly very afraid of what comes next. Jasper continues her motions, and Steven starts to pant. Before he reaches his peak, though, Jasper pulls out her fingers, making Steven sigh in exasperatioon. "Don't worry, it's time for the last step. You ready?"
"Ready for whaaaaaaaAAAAAAAAAAAHHHHHH!" He shouts as a much larger shape forces its way inside of him. When Jasper's hands grasp his hips, he becomes sure of what's moving in and out of him.
Jasper grunts, thrusting in and out with a shape-shifted shaft, and Steven's groans are a sharp counterpoint. But despite the discomfort of something so large moving within him, he can feel himself growing harder and ready to burst.
With a final shout, Steven groans out one last orgasm as a warm liquid fills up his behind. The young hybrid collapses onto the bed, dancing on the edge of consciousness, listening as the gems each file through to give him a kiss on the forehead, whispering one last "happy birthday" before leaving him to rest.
[That was...an interesting...gift...] he thinks before falling asleep.
So, that's what I came up with to finish out this series. I hope you're all happy. Remember, any pairing, any situation, any AU, etc etc...
FUCKERY! *bows for applause*