Hello, this was a request from GayseyCasey!
DISCLAIMER:
If you have a problem with Male Reader x Sans, then here are some options.
1.) Fuck off
2.) Don't read
3.) Just request your own ship. (Also I don't do OC x sans, only reader x Sans, or Sans x Sans.
None the less, enjoy!
(1639 words long!)

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Red (Underfell-Sans) x Male!Reader

~3rd person POV~
It was snowing outside, the cold air filling the room as a slightly chubby skeleton sat down on the sofa with a smaller skeleton male in his lap, a blanket draped over his shoulders before wrapping around the small male as if it was a burrito and they were the filling of it. The snow poured down like a thunderstorm, being unforgiven towards the trees and who ever was stupid enough to be outside at that time. The two males who sat on the couch were alone without a tall vexed 'Edge Lord'' around them. The males didn't know where he was and neither of them cared much- since they were distracted by the TV and all, and a horror show by the star himself, Mettaton. They cuddled closer, Red's arms around the small boy as loud screaming and crying came from the TV. (Your name) didn't seem to enjoy it very much but Fell was delighted by it although he wasn't much of a fan of the star himself. However, (Your name) did seem to enjoy the comfort that the taller skeleton gave off as he sat in his lap, turning around to face him and hiding his face into the warm jacket he wore. "Hm.. Did you want somethin' kid?" He asked, his head turning down to look at the smaller male in his lap.

You smile and shake your head, reaching your arms up to wrap your arms around his neck and leaning up a bit to plant a loving kiss on his cheek, his face flushing with a bright pinkish red cherry colored blush as his eyes went blank for a moment before white highlights appeared in his eyes. Studying his face you see that he looks drained and tired, since he had been using all his magic to fuel that red highlight in one eye socket the loss of magic had made him frail and tired without him even realizing it. He wrapped his arms around you and smiled weakly, nuzzling his head into your neck as his face still continued to show the candy apple red on his cheeks.

~Fell Sans' POV~

Staring down at the kid I felt a sense of comfort and want, the want to protect them and protect them. I was out one day 'working' my shift when he just came out of seemingly nowhere, he seemed lost but not scared, but he seemed to have immediately taken a liking to me, holding my hand when we walked off. Boss hadn't seemed to be much of a fan to him, not wanting him to even be in our- or even my life but I had actually put in effort for once in my life (Or rather how Boss would describe it...) and earned the respect to keep him. Of course we had now shared a room with separate beds and stuffed but he had taken up the habit of cuddling close to me instead since the snow storms lately have been colder and such. ...Nuzzling my face into his neck I could smell the scent of a fresh blanket leaving the drier radiate off of him. I felt so comfy, and the tv noises sounded like mumbling, not paying attention to anything except for (Your name).

I carefully wrap my arms around his lower waist, and stand up, holding the small male in my arms while he used his legs to wrap them around my waist while I walk upstairs, going to our room and laying down on my back with (your name) on my chest, his head laying down on my chest as he let out a happy hum of satisfaction, allowing his hands to grab onto the shoulders of my jacket.

He seemed so happy and calm, his tired eyes. He had fallen asleep, a cheerful feeling growing onto me as I shut my eyes in an effort to fall asleep.

. . .

I woke up to the small skeleton sitting on top on top of my chest, planting kisses all over my face multiple times as they smiled happily. I chuckles and tried to sit up before he grabbed my by the cheeks and pulled me into a kiss on the mouth. I was shocked and glared a bit, not out of anger but out of embarrassment but I still didn't bother pulling away from the kiss , not wanting him to feel ashamed of himself but rather not wanting to pull away..

Eventually he stopped and I sat up, pulling him close to me before leaning down to kiss them again, shutting my eyes as we kissed, It was dim out- well it was actually always dim so in normal words it was just dimmer than usual, and I could feel red smoke leaving my eye socket as I kissed him. He seemed to squirm a bit in my lap, gently grabbing either side of my jacket and slowly pushing it off of my arms, allowing myself to assist him in his attempt to pull it off.

He dropped it to the ground and pulled away from the kiss, yanking off my shirt and having the upper hand of the battle, witch I wasn't okay with. I carefully grabbed his wrists and flipped us so he was now under me, but began to regret my actions as I felt a pain in my soul about how I would feel later on if I hurt him, or harmed him in any way. Unlike my brother Papyrus, I didn't feel the need to harm or hurt others unless I had a well reasonable reason to do so, and began to feel beads of sweat appear on the forehead of my skull.

However despite (your name) wrists being cuffed by his hand he reached up and gently grabbed ahold of my cheek, rubbing it with his thumb to calm me down before I tried to sigh as well as I could before continuing. Thinking about what to do first I gently slid my hand up under the warm (choice of colour) turtleneck shirt he was wearing, gently allowing my hands to glide over his ribs, him shivering in response as his (choice of colour) soul showed through the shirt.

I gently lifted the shirt off of him, exposing his chest and some of his pelvis to me as he looked away, his hair (witch was made of magic) flaming up as if it was made of fire, the colour of it dimly lighting the room we were in, and our faces. I could see his eyes shut tightly, not out of him being a wuss but rather not knowing what to expect in feelings and touchment. I chuckled before lightly grabbing his soul, sticking my finger into it and licking it gently witch made him whine out loudly for more, deciding not to give him more but rather being even more gentle with it, by pulling my finger out of it and giving it small soft licks to it.
(Your name) opened their eyes and glared at me,

~Your POV~
I whined glaring up at Red, the dark chuckling from his mouth escaping him like a purring cat as he gently bit into it, suckig on it slightly before his fingers gently gripped the rim of my pants, putting my soul down on the messy bed side table near his bed before proceeding to gently pull down my pants before proceeding rubbing small circles on my upper ribs, causing me to shiver in delight. His hands gently grabbed my hips, slightly rubbing them before leaning down and gently licking my neck, sucking on it and nibbling here and there to prepare me for a painful bite, his teeth sinking into part of my neck and part of my shoulder bone, blood dripping out of the wound before being lapped up by his red tongue, the feeling of pain and pleasure running through me as his hand suddenly grasped the base of my cock and began to rub, causing my entire body to shake with a pleasurable pain.

~3rd person POV~

Fell gently kissed away the blood off of (your name)'s neck, before lapping it up again, his hand still rubbing his dick, gently pumping it as he stared down at him, going in for a kiss before gently sliding his tongue into (your name)'s mouth, having a passionate french kiss with you, his soul glowing brightly likewise yours was too. It felt amazing, the heated love between the both of you as the rooms were full of moans and pants, as you could feel yourself reaching the edge when he began to squeeze and pump your cock, gently digging each tip of his finger into it, your dick twitching as he clawed into your chest, and left a trail of blood behind, allowing you to climax onto his hand and the sheets.

You pant softly as he pulls away from the kiss, moaning softly as a string of saliva connecting both of your tongues as you stare into each other's eyes, still panting as you both calm down, the movement of your chest rising and falling as you shiver and moan slightly. As you both lay there, you feel the attraction between you two grow, closer together.

...

He pulls you close and plants a kiss on your forehead, a smile streched out across his face as he mumbles a soft "I love you.."

...As you shut your eyes you smile, feeling wanted and comforted, cuddling closer as he pulled a blanket over you and him. ...Happy.