The End of the World
The child has introduced himself by the name of Asriel. The child's appearance, plus their name, it can't just be a coincidence.
"toriel's son?" Sans wonders. Toriel's dead son, except not dead, apparently. If only she was still alive... he can't imagine her joy upon finding her son still alive. The weight of her death, of Papyrus and everyone, weighs heavily on him. The child had spoken of hope, and names that Sans knew but the child should not, like he knew everything that Sans had just endured. "..." He's so tired, he's not sure he has the strength to endure much longer, even with the faintest glimmer of 'hope.'
Light footsteps sound from behind him. Damn, they caught up fast. Sans pulls what remaining strength he has left in his heart, forcing himself to face them. The demonic human emerges, shadowed by the overcast moonlight. Their sleeves are long, dangling over their fingertips, but Sans can still see a glimmer of light from the tip of their knife.
"...Why does he recognize your name, and not mine?" They ask, just the slightest inflection betraying their interest.
After killing everyone, all they can think about is themselves.
"I guess it just means that Mom talked about me after we died, and not you," Asriel sounds remarkably calm, and doesn't seem to care about making them angry, despite facing a demon. "You lied, Chara. That took a long time. How many times did you LOAD?"
Chara stops, a few steps from Sans. Still looking at him, despite talking to Asriel. They shrug slowly. "Does it matter? I got it right this time. After I kill Sans, I'll finish the humans on the surface."
Sans waits for the human to start the fight. At the very least, he can make them work for their victory. And perhaps, there's a slim chance that Asriel's plan could work...
"And yet you're still talking about 'hope?' I'm not going to bring anyone back. Even though you've failed, do you think there's any chance you can win, Sans?" They watch him carefully.
"i mean..." Sans doesn't have the mental stamina to keep up with all of Chara's games. They warp the world just to see his reaction. The stronger his reaction, the more likely they are to mess with him. "dunno if it's about me winning at this point, but just stopping you. and at this point, if this kid here thinks he's got something to do that, i'm not ready to give up yet."
They actually grin lopsidedly at that. "Yes, of course. You promised you would 'stop me.' Winning was never part of the equation." The human actually looks at Asriel, for the first time since entering the ruins. "Az, why are you helping Sans, anyway? You hate Sans. Or are you just messing around, too?"
Sans backs away from both of them, letting them face off. He'd be lying if he said Chara's words didn't make him nervous. The two beings clearly knew each other, and likely had the same ability of time control. It could be an elaborate trick designed to give him false hope.
Asriel shakes his head. "I really hate him," he admits. "But together, we can stop you. So it has to be Sans."
"You hate him," Chara repeats. "I did, too. At first, he was just an obstacle. A real wall that I just couldn't seem to break. But each reset, I made a scratch on that wall. Each time I died, I hit just a little harder. Until finally, those scratches became cracks, and I eventually won. I... at that moment, when he finally died, I was so happy. I had to do it again. And... somehow, unlike the others, he knew I'd already won once before," they giggle hysterically, talking about a different Sans than him. "Killing him the second time was so easy, I didn't get how I'd died so many times before that. You were right, Az – being a god is great, but it's not fun if no one realizes it."
Asriel looks at him in a way he doesn't like.
"You never got that chance though, Az. So I can give it to you. Kill Sans. Or don't, just have fun. He might be stronger than you, but he's not stronger than me. I won't let him kill you."
A few seconds tick by as Sans waits for Asriel's answer. He has no defense to offer – cannot speak for another Sans in a different timeline, who apparently was a 'wall' for Asriel. But if Sans's last option leaves him, then he really can't stop Chara.
"I..." Asriel hesitates. "No! I'm not like you, Chara."
Chara and Sans both sigh almost simultaneously, both for very different reasons. "Az, come on... don't pretend like you've got a soul."
Asriel shakes his head vigorously, hands clenching. "At least I remember what it's like to have a conscience, and feelings! Besides, you... you'd probably just kill me, anyway!"
Chara shrugs. "C'mon... I would have let you kill him... the first time," they grin maniacally. "And I feel plenty of things. You're right – we're not alike. I have a soul." They raise their knife, taking a step forward-
Sans slams the human's soul away, to the wall. His entire body creaks with blue magic, worn out from earlier encounters. "now would be a great time for you to do your plan thing," he half-shouts to Asriel, keeping his eyes pinned on the human.
They're already collecting themselves, escaping his weakening magic, so he can't keep them pinned there forever.
Asriel gulps audibly, nodding his head. "I just need a little time!" He lifts his hands, six rainbow-colored hearts appearing around him. The six human souls... Sans's eyes flicker to what his 'partner' is up to, but the human is already moving, so he can't afford to watch for long.
"I'm going to LOAD! And undo all the destruction Chara has caused!" Asriel squeezes his eyes shut, the souls around him resonating with power.
Chara runs towards them with their knife. Sans can't tell if they're after him or Asriel, so Sans flings them back with his magic again.
"Load?! This is my world!" Chara shrieks as they hit the wall. "You can't do that! And even if you could, what would be the point?! You won't even exist to SAVE! I'll just overwrite over whatever you think you can do!"
Nothing happens.
The souls behind Asriel stop resonating. "...What?" Asriel holds out his hands helplessly. "Even with the power of the human souls, I can't... why can't I...?"
The human rises again. And this time, around them appears the same rainbow-colored souls. They hold out their hands, as Asriel had, as if to beckon to them. Sans half turns around, only to see Asriel with the same souls, though they quiver as if uncertain of their existence.
"twelve human souls?!" Sans's eyes widen. Only six human souls have died in the underground. He's certain of that. And yet... somehow, Asriel and Chara have matching human souls surrounding them.
"Can't you count?" Chara says. Sans looks again, and the human is right – the souls that Asriel holds have one key difference. Chara has a red soul in addition to the six others.
Frisk's soul... The seventh and final soul that was supposed to set all monsters free...
In some alternate timeline, the human must have taken all the other human souls. But in this world, Asriel has also taken them.
But two of the same existing, in different circumstances, is a paradox. The world itself cannot come to terms with something within it that originated from a parallel universe. And so, one of them must break...
"No...!" The human souls surrounding Asriel shatter, leaving just Chara's seven.
Not just that, but the monster child's own form begins to waver uncertainly, as if becoming a ghost. The human souls, which house unbelievable power, had been the key to his existence. Without them, he... whatever kind of being Asriel is, Sans figures Asriel will no longer be able to exist. The child clutches himself as if he might shatter at any moment... and he probably will, too.
"what's plan b, kid?" Sans says with surprising calmness. If Asriel only has a few moments left, Sans needs him to stay calm in case they have another way to defeat Chara.
"There's no other plan!" Asriel screams and falls to the ground, unable to match Sans's composure.
"You can stop pretending to be someone you're not, Az," Chara walks slowly towards them. "Asriel hasn't existed for a long time, anyway."
The souls around Chara flicker.
Chara stops, looking at them.
The six human souls, all except Frisk's, inch away from Chara. They fade out, and then... the souls re-appear next to Asriel. They surround the kneeling child, rotating slowly. Asriel's form stops shaking. Hesitantly, he looks up to the human souls.
"Impossible... the human souls..." Chara stares. "They... they belong to me, you can't just..."
Asriel rises, holding his hands as if praying. His body glows, like the souls, a strong magical power radiating through him and the souls. "I can feel it... Sans!" He smiles joyfully at the skeleton. "The human souls... they understand what we're trying to do. They want to save the world, too!"
Sans grins, the first real smile in a while. For the first time in a long time... hope floods back into him. They can win. For once, something isn't going according to Chara's plan. And... he can feel it, too. The desires of the human souls flood into him. The peace and happiness that they failed to obtain... they can at least help the rest of the world.
"It doesn't matter," the human has regained their indifference. "There's nothing you can do that I can't undo. So kill me, and I'll come back. LOAD, and I'll overwrite your SAVE. Don't you both get it? This still means NOTHING."
"No..." Asriel shakes his head slowly, still smiling. "There's one place Frisk can't return to, no matter how many times they reset."
Chara's eyes slowly widen, seeming to realize what Asriel is up to. "No, you can't do that."
"Sans! I'm going to send you back in time..."
"Reset!" Chara shrieks. The world fills with static, but remains in place. The human SOULS refuse to let the human use their power. "LOAD! RESET! Reset reset reset reset reset reset reset-"
They fling themselves crazily at Sans, knife swinging. Sans pushes them away with a blast of gravity again. If they're actually scared of Asriel's plan... then it must mean it will work.
"monsters... humans... everyone's hearts are banding together to stop you," Sans's smiles patiently at Chara. He's filled with an unbelievable strength; the hopes and dreams of the human souls.
"...Now. I'll send you to the one point where you could have stopped Chara. Only this time, you'll have all the memories you need to succeed!" Asriel cries.
The souls burst with power, washing over Sans and the world...
The world fades and ceases to exist.
But he can feel it... There's more. Memories he had forgotten in other timelines begin to come back to him...
