I was tagged to do this thing...I find a song...then make a story with it.The song that I chose was Stronger Than You,the Undertale version.It's a parody of the Steven Universe song under the same name.
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Bock...bock...bock...

The footsteps of the human echoed through the chamber.Their SOUL was darkened by LOVE and EXP.

There were a true demon now.

Maybe in another timeline we're friends...

"You know, kid..."Sans the skeleton leaned on a pillar,one eye closed."It'd be a crime if I had to go back on the promise that I made for you."

Frisk looked at him with a blank face,his hands gripping a knife.

"But you killed Toriel..."Sans growled,his blue eye looking for any sign of emotion."And Papyrus.Undyne...Mettaton...you killed them all.

Therefore,the promise no longer stands."

Sans hoped to intimidate the child,to make him just BACK OFF.

But instead Frisk tilted his head to the side slightly and a sinister smile appeared on his face.Sans shuddered,becuase when he first met Frisk,nobody could think that a child like him could make a smile so sinister.

"I made my choice long ago."Frisk laughed,twirling the knife in his right hand."I chose genocide.And if you beat me...I'll just reset."

"Then we'll be stuck here forever,fighting in this hall.Let's go,dirty brother killer."Sans growled.

They entered a FIGHT,and Sans knew that one hit,and he was a goner.

Whatever.It's a win-win situation.I beat Frisk,well,he doesn't pass.I die,well...

See you soon,Papyrus.

Frisk started off trying to swipe at Sans with his knife,but he dodged with ease.

"Too slow."He teased."My turn.This is going to hurt...a skeleTON."

He used his Gaster Blaster,and Frisk got hit,but it wasn't enough to take him down.

"I know you'll reset each time I beat ya,but I'll be right back here to meet 'cha."Sans said.

Haha.That rhymed.

Frisk swiped again,but failed.

"Gosh,I've seen a flower do better!"Sans shook his head.

The FIGHT went on,and Frisk never landed a hit.

Sans hit him with the Gaster Blasters one last time.

And Frisk's SOUL broke.

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I haven't actually played Undertale so...

...

Expect imperfections.