Notes: Thank you for all the kind reviews! I realized this works better as a single fic with oneshots, so this has been updated accordingly. The title has also changed!
Summary: Sans realizes things are repeating when he opens his journal one day and realizes there's already an entry for that day written down. Sans starts keeping a tally.
They show up in Snowdin one day because there's nowhere else to go. It's a nice place, everyone knows each other. And everyone treats Sans and Papyrus kindly. It's not home - not their real home - but it'll do.
Papyrus doesn't remember much of where they were before.
Sans wishes he was that lucky.
Sans builds a workshop behind their house. He fills it with the things he was able to salvage from before. Blueprints. Pictures. His badge.
The machine.
He locks it behind a door, and with it, any hope of going back to before.
Snowdin's not that bad, anyways.
Sans keeps a journal.
He's used to keeping journals, he used to do it all the time before, although he lost them all when he and Papyrus arrived. Still, it isn't hard to enchant a notebook so that the writing will remain, even if things start getting weird. It's a force of habit, just like dating his journal entries.
Sans fills the pages with noteworthy things about Snowdin. The teens in the woods. The Royal Guard. The names of everyone at Grillby's. The innkeeper who's always nice to Papyrus. The door deep in the forest, perfect for practicing knock knock jokes, and the woman behind the door, perfect for practicing jokes with.
Sans realizes things are repeating when he opens his journal one day and realizes there's already an entry for that day written down.
Sans starts keeping a tally.
After five loops, he unlocks his workshop for the first time. Papyrus gets angry he spends all night there, and Sans wishes he could explain things better, but it would be easier if Papyrus didn't get involved.
Timelines are stopping and starting, repeating and ending. But who? And more importantly, why?
Papyrus talks about a flower, in some loops. A fanclub, too.
Sans jots down a name - Flowey - and reminds himself to ask about it sometime.
Twenty loops go by.
Nothing changes.
Maybe the anomaly is just bored.
Thirty more loops go by.
The teens in the forest have disappeared. Papyrus has too.
Sans sits at the door to the Ruins, and when the end finally comes for him, he can't even summon the urge to fight back.
Who fights back against a flower, anyways?
Sans learns to remember that flower.
And he learns to start getting rid of it before problems can start.
The loops keep happening, but he takes a grim satisfaction in killing that stupid flower over and over again.
Fifteen more loops go by, and something finally changes.
A human walks out of the Ruins.
Sans knows he made a promise. But even then, he wonders, just for a moment, if it's worth it.
Then he changes his mind. Getting to the surface stopped appealing to him a long time ago. And even if he did get there, it's still not home.
He makes a new friend.
For a short while, no resets happen.
But then, strange things start happening. The loops are shorter and faster, only rewinding maybe a day behind at a time, sometimes even a few minutes at a time.
Sans gets a new journal and keeps a closer eye on the human.
He doesn't believe in coincidences, not by a long shot.
Sometimes the human gets a weird look in their eyes, like they've heard it all before.
Sans knows that look. It's the same look he gets sometimes, especially when Papyrus tells him to read his mail. Sans always has to resist pointing out he's read them all before. He knows every line in every letter.
But the human doesn't look tired.
They look filled with determination.
What's their goal? For the first time, Sans doesn't know. And the unknown makes him sick and hopeful all at once.
Maybe they have a shot of getting out of the underground after all.
At the resort, Sans has dinner with them.
He also threatens them. It's not like he doesn't like the human - he really does!
But he doesn't trust them. If they have the ability to change time, they're dangerous. They could destroy the whole underground.
He just wants to...warn them, is all.
Sometimes the kid starts crying. Sometimes they just look scared.
And sometimes, they just stare right back.
Sans isn't sure which makes him feel worst.
He judges them.
Asgore dies. Monsters are still trapped underground.
Sans always figured it wouldn't change.
Snowdin's not that bad, anyways.
A human walks out of the Ruins.
Sans finds himself meeting a human who turns to shake his hand first before he can even finish reaching them. Papyrus and Undyne seem to remember the human too.
Things are changing.
The barrier is broken.
They're finally free, they can -
A human walks out of the Ruins.
Sans finds himself meeting a human who is lightly covered in dust.
Something is wrong.
The human starts killing monsters. But not all at once.
Sometimes, the human seems to target a specific one.
Sometimes, Papyrus is the one that dies.
Sans wishes he could kill the human right then and there for it.
But he doesn't.
It's all going to be reset anyways, isn't it?
A human walks out of the Ruins.
Sans finds himself meeting a shambling human covered in dust, who stares at him with a blank expression.
Something is really wrong.
Sans tries to appeal to their humanity. Puzzles are nice, aren't they? Wouldn't they enjoy them, if they just tried?
Nothing works.
He tries to warn them.
They kill Papyrus anyways.
Sans follows them into Waterfall, watches as they slaughter every last monster there, watches as Shyren sings a warbling song and the human mercilessly kills her anyways.
He has so many chances, and he doesn't take any of them.
At the final corridor, Sans stands before the human. He doesn't want to do this. He knows there's no point in doing this. Everything will just reset.
But he's run the numbers. He's seen all the countless timelines that have ended. If he doesn't stop the human, everything is over.
He gives a final warning. The human doesn't listen.
He shows them a bad time.
He knows he can't win.
He keeps showing them a bad time anyways.
When the knife finally hits him, Sans finds himself at peace. It'll be nice to see everyone again - the people of Snowdin, everyone at Grillby's, Undyne, Papyrus…
A human walks out of the Ruins.
Sans stares at the human before him, and takes their hand.
He wonders if one of the other Sans-es out there is enjoying life on the surface, and if he'll ever get to be that lucky.
He probably won't be.
But hey, he's got all the time in the world to prove himself wrong.