i won't let you leave me【Yandere!Sans x Reader】

You finally meet him

He had only seen his soulmate for a few seconds-barely a glimpse and immediately fell in love. That's how soulmates worked. Your soul had left your body, lighting up your eyes briefly from the brilliantness of it.

For a few seconds-you smiling at him, him in awe-it was perfect.

So when your soul was crushed by a car before he could reach it, what little bit of mental stability he had left wavered. He started to feel his soul crack in heartbreak, his body turns to dust with his soul dissipating. Denial coursed through him, determined to prove that you were not dead, that it was not real.

And for a brief moment, his determination passed Frisk's, and a glitch reset button made of wingdings flickered for only a second-

But it was enough. Because with his frantic brain scavenging for any kind of hope-any glimpse that perhaps it was all a bad dream-the idea of having to live through everything again to get back to the surface didn't bother him anymore.

Sans couldn't live in this timeline anymore. Partially because of his magic going haywire and causing destruction, but mostly due to his own selfish need to be with you.

He was completely, and utterly broken. Unable to accept that you could be dead. That he wouldn't get to have a soulmate. To experience true happiness.

Of course. The world was giving him a second chance-most likely gaster-and he wasn't going to let it go.

He didn't care if it took a hundred more timelines for Frisk to bring them all back to the surface.

He didn't care that there was a chance for genocide. Because his body was melting, his brain already shattered in dismay and disbelief.

And he decided, this time, he wouldn't let you die.

He would protect you this time, and make use of this second chance he knew he didn't deserve but wanted.

"sorry, m' gonna make sure next time is perfect."

Before it could flicker away, he pressed it.

Everything went black.

And lit up once again.

Frisk saved them all.

Sans failed again.

Watched you die.

Watched you crumble into a pile of blood.

So he tried.

Again. And again. And again and again and againagainagainagainagainagain-

****

At this point, one would have to be living under a rock to not know about monsters. Their bright smiles as they greet the world after hundreds of years, and the small child leading them. It had been almost two years at this point, and everyone had settled and (more or less) accepted the new reality.

During those years many discoveries and progressions of technology occurred. But the most talked about, and rarest occurring one were soulmates.

Apparently, before the war that sealed them all underground, human 'souls' would be drawn to a monster one (or monster to a monster soul), where an unbreakable bond would match their age expectancy until one died and the other died from grief. Of course, this is extremely rare. The only reason this can happen is compatibility. Certain souls (apparently there were different colors?) would be able to bond with a specific monster's magic, making that monster more powerful.