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Sans isn't quite sure when this all started. He's been having the dreams now for as long as he can remember. You're underneath him, keening and whining as you grind up against him and whisper pleas for him to fuck you in earnest. He knows, deep down, that this can't be real. Still, he doesn't want to let it go for anything. He curls his phalanges into the sheets beside your head, presses his skull into the junction of your neck and shoulders. Your smell is intoxicating to him as he breathes you in. The scent of you snakes down along his spine and twines between his ribs, leaving him feeling filled to the brim with you. Your skin is warm against his bones. Or at least, he imagines it would be, if you were really here and this were a real moment shared between the two of you rather than just a dream.
Sans groans and grinds down against you, the friction seeming too soft and yet still sending tremors through him. He pants for air and clutches the sheets tighter, rolling his hips to repeat the motion. You let out a soft whine beneath him, clutching at his ribs and throwing back your head.
“Fuck!” The waking world crashes down on him too quickly. Sans finds himself with a hand shoved down between his legs for his pelvis to rub against as he ruts in his sleep. His bones seem to rattle with the need coursing through him as he remembers the visage of you in his dream, softly moaning his name and begging for his cock.
With an irritated sigh he reaches for his pillow, turning over and propping himself up with the pillow between his legs. His whole body feels stretched tight like the string of a violin and he knows there's no way he'll get to sleep until it's taken care of. He clutches at the sheets of his bed, closes his eyesockets, and thinks of you. He imagines the soft curves of your flesh. The soft arcs of your skin look so comforting to him. He wants to rest himself against you and trail his fingers across every inch of you, mapping you out so that he'll never forget. He focuses on that, on thinking about all the different bits of you that would be exposed as he unwraps you like a present. He thinks about your lips and the way they would feel pressing up against him.
As though with a mind of their own, his hips start moving, grinding down against the pillow while he imagines it's you. He's panting harshly, whole body trembling at the sensation of something pressing back against his pubis and it grinds down. “Fuck...Babe...need you...” He groans out.
He imagines you arching into him, babbled pleas about how much you need him too falling from your mouth. He imagines the way roll your hips back up into his as he ruts down into you. Sans has to clamp a hand over his mouth to keep back the sounds as he whimpers and cries out your name. He knows he's being selfish, knows you deserve someone who will go slow and take the time to pleasure you the way you deserve, but he can't help himself as he cants against the pillow and convinces himself he's thrusting into you. “Fuck, please...please!”
He's building faster and faster, begging and whimpering into his hand as he climbs ever higher towards orgasm. His hips keep thrusting forward and he thinks he probably couldn't stop them even if he wanted to. Instead he embraces the oncoming storm, body shaking as he nears the edge. His spine arches as he cums, phalanges clutching at his jaw so tight he thinks the bones may shatter. A low cry of your name escapes him, doing its best to leak past his fingers and into the open air of the night. His other hand clutches desperately at his sheets, the joints popping as they shift. Even as he cums his hips still move in shaky, aborted grinds against the pillow.
After many long moments, he collapses against the bed. His body feels heavy with the afterglow of his orgasm. He can feel himself lulling back towards sleep, even as the phantom feeling of your imagined fingertips trail along his spine. He could almost swear he hears you whispering to him about what a good boy he is as he drifts back off to sleep.