(Sans P.O.V) Sans knew it had to work this time. Once and for all this timeline will be purged of this demon child. He checked his cameras from his lab basement. The child is leaving the ruins! He had to get down there. He teleport's down the forest and greets them way he normally does. Whoopee cushion in the hand trick, then the lamp. He noticed they didn't do behind the lamp this time. He checked their LV. 3, they already have 3 LV. He cursed under his breath. They had initiated a Genocide route this past reset. This meant he had to hurry.
All throughout the forest his suspicions were confirmed, the kid was killing off every monster they came across. Finally they came across the bridge, where Pap's had his machine set up. Once again, the machine didn't activate and the kid continued on their way into snowdin. Before they did they stopped by him "heya kid, if you keep going the way you're going, y o u ' e"
He teleported out of the forest and back into his basement, where he continued to re-program systems and change functions. He looked up at his camera. The kid was just out of the shop, and heading down out of the town. He knew where they were going. To meet Papyrus for their battle. He didn't want to watch but it was like he couldn't look away from the screen.
Papyrus, like so many times before, gave his speech about believing the human could still be good. Sans watched as the Human moved forward once more and the battle initiated. He could see the look on their face. This wasn't just out of curiosity anymore. Sans remembers the first time they initiated a Genocide route. The look on their face was indecisive, as if they weren't sure what to do, but now he could see the look in their eye. They were now just doing this for fun, for the pleasure of it. It was sick and it sickened him almost to the point he wanted to break his promise before he was supposed to, but if this worked, then he wouldn't have to worry about that.
He watched with baited breath, as the human pulled back their fist, the pink-leather glove, wrapped around their hand. He watched as they swung toward Papyrus, and instantly destroyed his body. Pap's head fell to the ground. "W-W-Well, that's not what I-I-I expected, but I still believe in you, you can do better, I know you can!, you just have to try again" and with those famous last words, Papyrus's head disappeared along with the rest of his body.
He came out of his basement and walked down to where it happened. His dust was resting in the ground, almost as if the dust just came out of nowhere, but Sans knew better. Papyrus's scarf was stuck under a clump of snow and was peaceful looking, as if Papyrus had dropped it because he didn't tie it right, and was just looking for it around Snowdin. Sans would find it and take it to him. Pap's would thank him, give him a huge hug, and the pair would go into the forest for sentry duty. Sans scooped up the dust and put it on his scarf, wrapping it up like a bindle, and carried it into the house. He took out the left over spaghetti that papyrus had made last night. Sans was so proud of him, because for once, it had flavor, and texture and was more than frozen noodles with ketchup. Papyrus was bragging about how it was his best one yet, and it was, so it should be savored for as long as possible. Sans scooped out some dust, and warmed up some of the spaghetti. He then took the dust and sprinkled some over the spaghetti. He chuckled because it just looked like he was putting on Parmesan, not the remains of his dead brother. He smiled at the thought of how Papyrus loathed Parmesan cheese. He would always sprinkle some on his plate whenever it was made, sometimes just to spite Papyrus, and because he liked it. Papyrus would get mad and say something like "Sans!, don't do that!, it ruins the flavor of the Spaghetti!". Sans would chuckle and try a bite with the cheese on it and say "Heh you're right bro, I don't think I can eat this, seeing as it made such a cheesy gesture at me". Papyrus would scold him for the pun, and for putting Parmesan, but would laugh and sit down to eat anyways.
He took the plate of spaghetti and put it on top of the fridge. It didn't matter, everything would reset eventually. He went back down to the basement, and checked his cameras. The kid had already made it past Gerson's shop and was in the hallway of echo flowers. He had to hurry. He continued to work and watch the kid the same time. They walk past Temmie village where the room goes dark and they encounter Undyne, only for the Monster kid, to once again, get in the way and be carted off.
Sans watched as they went up to the bridge, and the Monster Kid called out to them. Sans watched the humans face carefully. Every single time, whenever the Human fought Monster Kid, the look on their face was always sorrow and regret, but this time the human didn't even hesitate as they rushed forward and stuck out their foot, ready to land a blow to his face, and always at the last second, Undyne would get in the way, and Monster Kid would leave. Every time, he would watch in amazement as Undyne transformed, while speaking to the human with such a powerful voice that even he felt inspired to go and help her, but sadly, he couldn't interfere.
7 times. That is how many times he felt time go back a little. He caught himself repeating actions, or recounting swears he took the same drink of coffee every couple of minutes. He watched as the human initiated the Undyne fight once more, and started to deliver killing blows. He watched as Undyne just took each attack like it was nothing, but Sans wasn't stupid. He knew, that even though Undyne had high stats in this form, that no one was invincible.
He watched as The human delivered the killing blow, and Undyne stood shaken. "d-d-damn it!, not even that power was enough?...well, if y-y-you think that im gonna give up, you're wrong! I've got my f-f-friends behind me. Alphys said she would watch me fight you, and i-i-if anything went wrong, she would e-e-e-vacuate everyone!, by now, she has already called Asgore, and told him to absorb the six human souls". Undyne was melting now. "a-a-and with that kind of power, THIS WORLD WILL LIVE ON!" She was smiling her biggest smile, even as she was dying, because she knew that even though she had lost the battle, the war was far from over.
Sans watched carefully as they made their way into Hotland. He saw them talk with Mettaton and continue out into the next area. They walked all through Hotland and finally made it to Mettaton. He watched, as he's done a thousand times before, as Mettaton transformed into his original form. He watched, helplessly, as they pulled out their gun, and fired six shots in quick succession. The lights faded out and Mettaton was shaking. "S-s-s-o, I gu-gu-guess you don't want to join my f-f-fan club?" and with those last words, an explosion rocked the area. He watched as the human continued down their path. He had to hurry, because at this rate the human would be at the judgement hall before he could finish. He watched as they found their way through Asgores home, and unlatched the key, all while the weed was telling them the story of how he died.
It was done, he had finished it. He looked up at his camera. His stomach turned into knots. they were at the Judgment hall, walking through it, about to stop and be prepared to greet him. He had to get down there now or the kid would reset and he would have lost so much progress. He teleports in at the last second.
"Heya, I see you've been busy. So, can I ask you a question?" He went through with the normal mantra. "Do you believe that even the worst person can change?", that anyone can be good if they just try?, heheheheheh, Ive got another question for you" He said. "Do you wanna have a bad time?, because if you take another step forward, you're really not gonna like what happens next"
They step forward, as they always do. "whelp, sorry old lady, this is why I don't make promises". He saw the world go dark around him as the battle was initiated. He picked them up, slammed them into the ground and went through the battle as normal.
12 times. This was how many times he had killed them. He knew it in his gut they were getting close. It was this one for sure, that they would land a hit. He watched as the human managed to dodge his ring of Gaster blasters. He saw waiting patiently, as they knew he would fall asleep, he tried his best, but years of laziness had that affect on him. He fell asleep. He managed to dodge the first strike, but since his turn ended they got another strike, and it landed perfectly. He got up. "huh, guess that's it then, whelp, I'm going to grillbys. Papyrus?, do you want anything?"
He stumbled out of the hall and teleported back to his basement. He was running out time, any second now he would be turned to dust. If this worked the world would reset, but the Human wont reset with it. He typed in the remaining variables and activated it. He felt himself being reduced to dust as the world around him was filled with a blinding bright light.