-UF!Sans is in for a surprise (Bottom UF!Sans)
When Sans from another timeline awoke and found that he was one again in bed with the human from the other timeline, he couldn't have been more ecstatic. He did enjoy the threesome last time he had been here with her and other him, but truth be told, it would've been much better if he had the human all for himself. And now that she was here alone with him, Sans threw off his jacket with the biggest grin on his face.
What he wasn't prepared for, was for this.
"Seriously, other Sans? Did you really think I was just going to let you have your way with me? Mm... Oh wow, you're tight...! Has other me not done this with you yet...!?"
All red Sans could do was whimper and moan as he tried to figure out how he ended up on his chest, his ass in the air while he was getting the lights fucked out of him from behind. His hands were bound down by what looked like two, blue phantasmal hands and what felt a little too much like a ghostly dick was plowing him with no mercy. He felt the human still for a moment to drape herself over his back and bite his trembling clavicle, causing him to cry out again.
None of this made sense. He should've been the one dominating her. He should be the one making her cry out his name. But none of that mattered anymore as the human continued to whisper things into his ear—such dirty things—and he broke down.
With one last whine, he cried out, "O-Oh god, p-please for the love of god j-just fuck me! I-I-I need your dick r-ramming into me! P-Please fill me with y-your cum a-and... and...!"
Sans didn't even have to imagine the grin that must've been on the human's face as she chuckled.
"Well, since you've asked so nicely... Nnh, I'm going to destroy you, other Sans."
And he couldn't have been happier when she did.
-Mirrors are fun (Sans decides to bring a giant mirror)
When Sans said that he wanted to get a better look at you when he was fucking you, you imagined that it was going to be something embarrassing, sure, but this was far beyond what you thought he meant. After enough foreplay to get you dripping wet, Sans had hoisted you up on his lap while your back was to his chest, his towering cock ready to penetrate your entrance twitching in anticipation. What you weren't ready for was him to use his magic to bring over the large mirror sitting across the room, setting it only a mere foot from the both of you.
"Shh, just watch."
With that, he slowly began pushing his thick member into you, keeping the pace painfully slow so that you could feel and see your tight lips spread wide to accommodate his girth.
You felt your face light up at the sight as Sans intentionally moved his hips so that you could get the best view of him languidly fucking you. Each thrust was accompanied with a small whine, your pants getting more shallow by the second from seeing every inch of Sans' phantasmal cock being massaged by your tight walls. The embarrassing sight and Sans' pace only drove you more wild, and when you do cry out your first peak, Sans kept his hand on your jaw to make sure that your eyes were glued on the mirror.
-Tentacles are fun (Sans makes tentacle dicks)
Sans had mentioned it from time to time that because his dick was made with magic, he had free reign over what kind of shape it took. You had first hand experience with this, such as the time he expanded it to close to twice its original size that it had pushed itself past your cervix, or the time he had been in heat and created two phantasmal cocks to burn through the heat faster. So when you had asked Sans what else he could do with it, the giant grin on his face should've been an indicator of what it would entail.
You whimpered and bit into the pillow as one writhing member—a tentacle shaped member, for that matter—filled your vagina, pushing against every inch of your inner walls that seemed impossible by human standards, and another equally squirming one was pushed into your other orifice. It felt as if you were about to burst from within, but Sans was good at controlling his magic. When the sensation was becoming too much, he eased off, ceasing the writhing of the two tentacles or decreasing their sizes so that you could have a breather.
"Saaaaans..." you whined, pushing your hips towards his. "C-C'mon... I can take, nnh, I-I can take more."
"Oh? You sure, kiddo? Can you really handle it...?" you heard Sans growl in your ear, sending another shiver down your spine. "Well, how 'bout this one for you?"
Another sharp moan escaped your lips as you felt another smaller tentacle slither forward and flick at your sensitive clit. "Aaah! S-Sans, h-how many of those can you make—mmph!" Your voice was cut off as you saw a flash of blue and another, thick tentacle was thrust into your mouth.
"I can make as many as you want... Ahh, yeah, I like it when you lick it like that...!"
Quickly your mind became muddled into a lust filled haze again as Sans began moving all of the tentacles at once. Eyes lulling back at the immense pleasure bombarding you from within and from without, you leave a mental note somewhere in your mind that you'll need to ask Sans to do this more often.
-Things get out of hand (Exhibitionism)
Along with exceptionally bad puns, it seemed that Sans enjoyed pulling pranks from time to time. The whoopie cushion in the hand trick that he pulled on you when you first met underground many months ago had been one example. (Could the adding incidental music in Papyrus' life count as well?) you wondered time and time again. However, ever since you two officially started dating, Sans would try and pull off more daring pranks.
It started innocent enough. A quick hug here, a sneaked kiss there, a playful smack on the butt when you passed by him in town... That sort of thing. But considering Sans' personality, it didn't end there.
You weren't sure how Sans pulled it off. By "it", you mean how he managed to sneak his magic into your panties to create a thinner than usual member on it. Had it not been for the pure shock of it suddenly materializing and plunging into you, you would've surely cried out lewdly in the middle of the supermarket. You had fallen to your knees at the sudden rush of pleasure coursing through your body, and on the contrary, Sans had feigned ignorance and rushed to your side in concern. You still caught the hint of a smirk on his face, along with the tint of blue in his left eye, proving that he was behind this.
No amount of glaring or whispered chastising words helped. Sans continued to help you get groceries while feigning the role of concerned boyfriend when he was the one causing the member inside you to writhe. At one point, the pleasure became too strong for you to fight off and you collapsed in Sans' arms, vision tearing from need as you pleadingly looked up at him.
Within an instant, you were swept up bridal style and in the next instant, he and you were in a small, dark room that seemed to be some kind of closet. Sans had used a shortcut to the backroom of the supermarket. After a heated whisper into your ear to keep quiet, everything became a blur.
Your jeans were yanked down along with the panties with the phantasmal member on it, and in one swift movement, your body was lifted up and pressed against the wall as Sans sheathed himself inside you. Stars flashed across your vision at the wonderful sensation of being filled to the brim, making you want to cry out. Still, the sounds you could hear from outside the closet reminded you of your current situation and you quickly bit into Sans' jacket to keep yourself quiet.
The coupling was fast paced—neither you nor Sans had a wish to be caught, after all. Sans' heavy breathing at your ear in addition to the frantic movement of his hips as he mercilessly pounded into you compounded your pleasure. Thus, it wasn't long before you reached your peak, followed closely by Sans cumming deep within you.
It's not even a few minutes afterwards that the short skeleton pulled himself out from you and slipped your panties and jeans back on... all the while leaving his seed in you. He gave you another teasing smirk before you realized that you were both standing in the unchecked areas of the supermarket again. Sans took your hand and nonchalantly continued on with the shopping, obviously enjoying your brightly flushed face from feeling the sticky cum slowly seeping out of you.
Oh, you were going to get him back for this some day! You weren't sure how, but you were definitely going to make him pay for this prank sooner or later.