So I'm joining the Undertale fandom a little late, but here's a story set in the AU where you fight Sans in Snowdin instead of Papyrus, who you fight in the Last Corridor. Obviously, it's part of the genocide route.

Thanks to WolfHowl091, because if she hadn't put up with my constant questions and doubts about this, it wouldn't be finished.

"Hey kid."

You stare at the skeleton, his form blurred through the thick fog. He stands at ease; slouched over, hands shoved in pockets, a lazy grin on his face. He knows what you are - what you've done – but if you didn't already know you would never have guessed. His relaxed demeanour is unnerving, and you subconsciously tighten your grip on the handle of your knife.

He shuffles slightly, his slippers crunching through the snow. The sound is like a warm knife through butter as it cuts through the silence. "So, having fun?" he asks, voice jovial as always. "I guess you are, judging by the wide smile you've been wearing as you slaughter innocents." As your eyes widen, he smirks. "Oh yeah, I've been watching. I've seen every slash, stab and slice, every single monster in the nearby vicinity crumble to dust. You're leaving no stone unturned in your quest for LOVE, are you?"

He quietens for a moment, as if gathering his thoughts. You risk tearing your gaze from the bony figure to glance at the blade of your knife; it's coated in the dust of those whose lives you stole. He isn't wrong; you backtracked a couple dozen times just in case you missed a chance to gain more EXP. Your legs ache from trudging through mounds of snow and the knife feels like lead in your hand.

"It's happened too often now," the skeleton says, slapping you out of your thoughts and back to reality. You hastily draw your attention back to him, mentally berating yourself for your temporary loss of focus. "Over and over," he continues, seemingly not noticing your short distraction, "he dies. Time after time after time. I think after every reset, 'maybe this time will be different'. I hope and I pray, but to no avail."

"Every single time, you kill my brother."

Your hand clenches around the knife handle again as a feeling rises within you. It surely can't be guilt; it's far too late for that. You're much too far gone.

The skeleton hunches his shoulders. "It always plays out the same way. You come through the door, skip through my brother's puzzles, then reach this area. Every time, he appeals to your humanity." He let out a short bark of laughter. "My bro always sees the best in people. I don't know how he does it. It was his downfall with you, though. Every time, he spares you, and every time you murder him."

Your hand starts to shake and you find yourself unable to quell it. All you can do is hope he doesn't pick up on the tremor, on your weakness.

The skeleton's voice softens. "He believed in you," he says, his voice a mere whisper. You can barely hear his words over the howling wind. "He always believed in you, and you always struck him down without a care. Do you have any idea how I feel? Knowing what's coming, but being unable to do anything. The crushing feeling of hopelessness… I can't take it anymore. I can't lose him again."

"So here I am."

His eyes properly meet yours for the first time, the lights dulled with a never-ending grief. "I sent him off to help evacuate. He wanted to be here to fight you, but I wouldn't let him. He wasn't exactly happy, but I'd rather he be unhappy than dead."

He sighs loudly, as if tired of it all. "You'd think I'd learn from my brother's mistakes. You'd think I'd kill you before the monologue, before you had the chance to kill me first. I owe it to my bro to at least try, though, so…"

He removes his right hand from his pocket and holds it out towards you, palm up.

"I made a promise."

You stare at the skeleton, confused by the unexpected move. You watch the bony hand as it hovers invitingly. Suspecting a trick you stay alert, frozen fingers still tight around the knife's handle. His smile appears to, if anything, shift from menacing to comforting as he stands with arm outstretched.

"I promised," he continues, "that if a human walked through that door, I would spare them."

As he speaks you jerk your head up to look him in the eye once more. Why he would make such a promise is beyond you, when he remembers all that you've done. When he knows what you are.

"It doesn't have to be this way," he says quietly. "This can end, here and now. All you have to do is drop the knife. Put it on the floor and walk away. That's it. You can do that for me, right… friend?"

You stare, unmoving. He cannot be serious. After everything, all the murders you committed, all the EXP and LOVE you gained, there is absolutely no way he would offer you mercy.

It must be a trap.

Somehow though, even with that knowledge, you still find yourself considering it. How easy it would be to finally unclench your hand, to let the knife fall to land harmlessly in the snow. You would finally be free from this endless cycle of hate, destruction and death.

No.

If you accept his mercy, you will die.

You have no choice.

In one fluid motion you attack, arcing your knife in a downward slash aimed at the skeleton you once called a friend. He throws himself to the side, and you glimpse the sad smile he displays as your knife passes by harmlessly.

You spin, desperate to gain the upper hand. Moving faster than you ever have before, you throw your arm toward the sky, the knife cleanly scoring an incision up the back of his spine.

He staggers forward as the bone cracks and flakes, hand flying back instinctively to hold the wound you inflicted. He makes no sound, but he doesn't need to. You step back as he collapses face-first into the snow, no longer able to support himself. Still he remains silent, even as he forces his head up so he can support it with his free hand while escaping the face full of slush.

The silence is deafening as you stand there, just watching him. His position cannot be comfortable, folded in on himself like he is, but the damage you dealt to his spine renders him unable to move.

After what feels like an eternity of nothing, he laughs quietly, lacking the energy for anything louder. "I should have known it would end like this," he wheezes into the raging wind, rapidly losing the little strength he has left. "Why bother appealing to your humanity when you're just a demon in disguise?"

You force yourself not to react, not to show emotion.

"I warned you-"

He breaks off, hacking. Each cough causes more of his broken spine to splinter and fall off. "He won't forget this," he hisses. "I warned you. You're gonna have… a bad time..."

The skeleton's body pulses, converting into dust. As the bones crumble and the pile of dust gathers, you here one last word spoken into the wind.

"Papyrus…"

He is gone, leaving only his signature hoodie coated in golden dust.

You force down the rising wave of feelings, steeling yourself. You turn slowly, body aching, and walk numbly through the fog, away from the remains of your old friend, willing yourself not to care.

You don't need Sans watching over you, judging your every move.

You judge yourself enough for both of you.