"Cold," was all that Sans thought as he walked through Snowdin. He stopped for a second and pulled his jacket a little closer to his chest, continuing to walk through the quiet and empty streets, feeling the light wind whistle through the trees as it ruffled his jacket. He heard the light crunch of the snow under his slippers. He was thinking, thinking about what happened today. It had been a long day.
It started normally, he woke up and was greeted by his brother making breakfast, spaghetti as usual. He choked it down and walked with papyrus to his sentry station, after which papyrus left to check his puzzles. Sans, as usual, took a nap at his station, preparing to sleep the day away. But then a strange thing happened: he heard the ruin doors open. This has never happened before, so it startled him a little. What startled him even more was what came out: a human.
He'd never seen a human before, but he'd heard about them. He also remembered that promise from the lady behind that door. Curious, he decided to follow them. He noticed something strange right away; even while following at a distance, their movements seemed a little hollow, though he could not explain what that meant. Their clothes looked dusty, as if taken from an old wardrobe. It weirded him out a bit, and when he walked over a stick and made a loud crack, they didn't seem to react at all.
When he caught up with them, he said, "Human, don't you know how to greet a new pal, turn around, and shake my hand?" He extended his hand with his usual hand-whoopee cushion. When they shook it, it made a loud fart noise. The human made no reaction at all. This unnerved Sans quite a bit. He chuckled as he said, "The old whoopee cushion in the hand trick, it's always funny. That's uh, your cue to laugh, or, uh, to emote at all?" He noted their lack of emotion, but continued by guiding them through the bars his brother made. He noted another strange thing: when he told the human to hide behind the lamp, they didn't move at all. That was when he got the suspicion that something was terribly wrong.
"Heh, wished I'd been a bit more forceful," he thought, snapping back to where he was. Recollecting the day wasn't doing him any good. He was walking through the forest part of Snowdin now, the part where. He sighed and stopped, standing in the spot where the human had stuck his brother down. There was nothing left of him but a pile of dust. He sighed again and pulled a bottle of ketchup from his jacket, taking a small swig. "Alphys has probably evacuated Waterfall and Hotland now, which means the human is probably on their way to the throne room," he thought as he put the bottle back. "Guess I got to go do my duty, see ya soon, bro," he said as he gave a small chuckle and took a shortcut.
Appearing from behind a pillar, he stood against the pillar and simply waited. He had some time to think about what to do now. He had made a promise to never hurt a human, but the actions done, the lives lost, did that promise even matter now? He wasn't even sure it was human anymore. No matter, he knew he couldn't do anything anymore; his laziness had limits. He thought about the timelines, the reports he saw from Alphys's lab. He saw how the human was making the timeline unstable, causing errors. He knew he had to talk to the human, try to fix this, even if he couldn't remember what had happened exactly.
He heard the sound of someone walking, and knew what he had to do. He stood up and walked into the center of the hall, firmly in the Humans' view as they stopped in their tracks. "Heya, you've been busy, huh?" He asked them rhetorically as he looked into their blank expression. He had the strange feeling as he talked to them that they had heard them say this before; he didn't know why, but when he watched their looks, they looked almost bored, like this was almost routine for them. He continued his little speech, even dropping a warning before he finally unleashed his first attack. To his surprise, they dodged it all on the first try, with almost no effort, like they'd seen it before. As the fight continued, they dodged all his attacks with the same graceful ease. No matter what pattern of bones he used or blaster he tried to hit them with, they didn't get a single scratch on them. He was getting exhausted from fighting, but they didn't tire out at all.
Deciding to try talking to the human,
Sans halted his attack and attempted to reason with the human. He asked them if what they were doing was worth it and reminded them of the friends they once had, and decided to offer mercy. He could already tell partway through this talk that it wasn't getting to the human at all. They had that bored expression on their face again and simply waited for him to stop talking before they came in for another attack. He sighed, knowing that at least he had tried to reason with them. He started resuming his attacks again, mixing them up with his shortcuts and his skeleton-esis (heh.) as he slammed them into walls and teleported around, but nothing seemed to work. He decided to pull his final gambit and released an all-out attack, shattering tile and pillar as he used all that he had left up his sleeve, that is, except for his special attack. When it was over, he simply decided to use his final method, not giving the human a turn to attack and simply waiting out, as long as it would take to make them bored and quit, though Sans wondered if this would even affect them at all, and they already looked bored.
He just stood there and waited, feeling himself breathe heavily and sweat from all the exertion of using his attacks for the first time in a while. He began to yawn as he felt himself get exhausted from the adrenaline of the fight wearing down. He had tried throwing everything in his power, his opening attack, his blasters, even the fake-out spare. None of it mattered, though, in the face of this beast of a child. He breathed heavily as sweat dripped down his face. Sans finally thought, "Time to use the special attack, huh?" and hit them with everything he had. Finally, the dust had settled in the hall, and as Sans looked on, the kid emerged completely unscathed again. Sans was flabbergasted; they'd survived again. He trapped their soul in the battle box and began talking, explaining his special attack and telling them to give up. Finally, he just had to wait, wait out the human. "God, I'm tired," he thought to himself as he began to feel his breathing slow down and his eyes droop. "What's the harm in one nap?" he thought to himself as he finally closed his eyes and let rest take over his eyes.
SLASH! The sound of the knife slicing through the air hit Sans as he barely managed to dodge out of the way of another attack. Turning to the human to mock them for the miss, he watched in horror as the human turned their blade and unleashed another attack. He felt the blade tear his bones and rip his jacket as ketchup spurted out of him. All he could do was gasp out and collapse onto the floor. His attacks, his talking, all of it was worth nothing. He thought about how this meant all of his efforts were doomed. Looking at his red-stained hand, he simply looked up at the human and said, "Welp, guess that it's it, huh, just … don't say I didn't warn you." He picked himself up and began walking away. As he neared the end of the corridor, he saw a familiar face in a glimpse as his legs finally gave out and his body began to fade. All he saw was a large smile, and then a fade to black.