Title:
"The Broken Promise"

"Hey Sans"

"*Yeah (Y/N)"

"Have you ever thought on what could actually happen when we're on the surface. . . . like what if the humans still hate us... would they even let us stay on the surface...would they still hurt us...would they declare war again...would they trap us here again or. . . . .would they like to befriend us to have peace once again with them and let us monsters achieve our dream to see the real stars and not this once in the undergrounds"
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"Sans are you alright"

"*Yeah I'm fine but (Y/n)"

"Yes Sans"

"*You know I hate making promises but I'll make you an acceptional"

"Ok so what's your promise"

"*To bring you to the surface and to....love you and only you"

"....if your making promises then I will as well"

"*Ok so what are you going to promises"

"Wait for a sec I'm going to put it in an echo flower so we'll both remember our promises"

"*Ok,but can I hear what your promise is"

"Ok I,(Y/n)(L/n) promise to love you and only you and I will never and I mean never leave your side now and forever"

"*....you really mean that"

"of course silly why would I promise something that I would easily break"

"*Heh guess your right"

☆ The Day before Frisk came to the Underground ☆

"Hey Sans have you been feeling strange like something bad is going to happen",I said as I swing my skeleton legs as I was sitting on top of the table of Sans' post(Sorry forgot what its called pls correct me if I'm wrong).

"*Yeah but I think is just nothing to worry about", Sans said as he drinking his ketchup.

"Ok Sans I trust you"

•°☆ The Present ☆°•

"Sans I heard something in the forest lets check it out"

"*ok (Y/n) but we have to hide on the trees got that"

"Ok Sans now c'mon"

"*ok"

As we teleport on a tree we both saw a human whose hands are covered in dust with a knife on there hands walking out of the ruins door.

"....S-sans do y-you think the h-human killed everyone in the ruins especially the old lady"
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"S-sans are y-"

"*I'm fine and yes I think that kid killed everyone in the ruins I think we should kill them but we have to keep an eye out to see if they are doing a genocide route"

"O-ok Sans"

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*Crunch

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"*Friend don't you know how to greet an old pal turn around and shake my hand", after Sans said that the human turn around and shake Sans hand.

As the human grab Sans hand a sound was made "*Pffffffffffffffffffffrrrrrrrrrtttt".

"*Heh the old whoopie cushion on a hand trick classic. So Hey names Sans, Sans the skeleton""And I'm (Y/N),(Y/N) (L/N)"

♤Frisk/Chara's fight with Papyrus♤

Y/N POV

I was watch the human while Sans is somewhere. Sans told me to watch the human before he disappear without telling me what he's plan.

As I watch the human I saw that they were about to fight Papy. I thought they were going to spare him but I was wrong,so wrong.

After the human killed Papyrus they were about to go to waterfalls but was stop by a walls of bones.

"Why?"

"Why would you kill innocent monsters huh? WHAT DID THEY DO FOR YOU TO  KILL THEM!?!"

"This time I won't hide or watch you kill innocent monsters this time I.WILL.END.YOU"

As I finish what I said. I used my magic to summon bones and Gaster blasters.

They tried striking me countless times. I manage to dodge their attacks some manage to cut me but I didn't gave up for I was determine to end this.

We continued fight, As I send another wave of bones which they manage to dodge.
  They strike me. I however wasn't fast enough to dodge the attack.

"Ugh..hehe...he....didn't...s-see that...o-one coming..."
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"S-s-sans...I'm..s-sorry....for...b-breaking.....my........p-promise......to............you"

♤In the Judgement Hall Sans Battle♤

Sans POV

I was standing here waiting for the kid to arrival.
'That kid is so dead after why did that kid reset? Why did they chose the genocide route? We were so happy on the surface WE finally saw the stars and live in peace

I'm sorry everyone I couldn't protect you all especially you (Y/N). I couldn't protect you and thank you for atleast trying'

I was snapped out of my thought as I heard the kid's footsteps. Shadows was cast over my eyesocket as I spoke to them "*kid why would you reset were finally have peace but you go and reset so why? Aren't satisfied that you go and reset back then kill everyone"
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"*So that's how its gonna be"
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"*sigh....welp since you don't regret what you did. YOU'RE GONNA HAVE A BAD TIME"

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And done finally done with my 2nd oneshot story any ways thats all and I think I'm gonna make a second part of this not sure but  you can comment if ya want a second part or request so thats all for now

❤~See ya next time my beautiful butterflies