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simulation theory

Summary:

He's back.

And how could Asgore ever forget? The realization had struck him like a ton of bricks on his way to the throne room, the gaps in his mind suddenly filling, the name on the tip of his tongue in his grasp as if it had never left in the first place. Memories of a time long past bloomed in his mind like roses with sharp-tipped thorns.

Gaster.

Asgore has lost everything. His children died, his wife left, and his closest confidant has been missing without a trace for over a decade. The weight of the entire Underground rests on his shoulders, and terrible sacrifices had to be made for the good of monster-kind.

The final child has fallen from the surface world. The man who speaks in hands has returned – and he brings a warning of impending danger that has apparently destroyed the Underground many times before. He won't let that happen again.

Notes:

I started this way back when Undertale came out, if you can believe it. I even published it on AO3, but that version of the fic now rests in a hidden Private Works collection and I've finally decided to rewrite it.

Hope you guys enjoy! Concrit is super welcome.

A few notes on headcanons before we start: Gaster isn't a skeleton in this one, nor does he have any direct "blood" relation to Sans and Papyrus. The main focus here is Asgore, Gaster and Chara, though Alphys will have a bigger role to play as well. I know a lot of people don't like the Evil Chara headcanon, so heads up - that is the headcanon we are rolling with here.

(See the end of the work for more notes.)

Chapter 1: fallen down

Chapter Text

"A human has fallen from the Surface World!"

There wasn't a single thing Asgore wanted to hear less at that moment. Papyrus, bless him, didn't seem to notice the tension in the air, the stillness that had settled over them as soon as he'd mentioned human; he was too busy looking to Undyne for her approval. He received a half-hearted thumbs-up. Pleased with himself, he sat back down, sending an expectant glance into the round.

Everyone of import was gathered for something of a crisis meeting; Asgore himself, of course, as well as Undyne, Alphys, Sans and Papyrus. The latter was only here by virtue of the fact that the human had passed through Snowdin, right into the skeleton brothers' territory, and Papyrus was taking his guard duty about as seriously as he could possibly take anything.

"What can you tell us about the human?" Asgore asked cautiously, addressing Sans, but receiving an extremely long-winded response from Papyrus instead. Apparently, he'd gone on a date with the human. Or something. The way Papyrus' mind worked was a bit of a mystery to all present, and most of the information was very far from actually helpful.

"She was a human of very few words!" he chirped, "Which is unfortunate! I really wanted to talk to a human!"

"Thank you, Papyrus," Asgore said with a nod of appreciation. The tone he used was one that he usually reserved for talking to children, but Papyrus visibly appreciated it nonetheless. "Would you like to step out and keep watch for us?"

The tactic felt dirty. Papyrus was a very appreciated member of the Underground, no doubt, but he also wasn't exactly famous for knowing how to keep his jawbone shut on sensitive matters. And a human falling into the Underground for the first time in years? That was a sensitive matter indeed. It was enough that he knew. But then, the human was running free anyway, so it was only a matter of time until word spread.

Papyrus, being Papyrus, accepted the dirty tactic without even a trace of doubt on his features. He left happily, a spring in his step, wind fluttering under his red cape.

"So," Undyne began, "What will you have us do about the trespasser?"

Asgore sighed. "You know what to do. What needs to be done."

"We only need one more soul to break the barrier," Alphys supplied, voice thin and form awkwardly hunched together as though she'd rather be anywhere but here. Asgore shared that sentiment tenfold, though he took care to square his shoulders and keep his voice level.

"Then the barrier breaks, and we're free." Asgore didn't miss the hopeful glint in Undyne's eye as he spoke. He also didn't miss how it withered and died seconds later.

"And then what?" she asked.

That question was somehow even worse than the initial question that brought them all together, of what to do with the human. Take its soul, obviously. Break the barrier. That had been their one and only goal for decades. But what then, indeed? They were hardly strong enough to mount another war with the humans - a war that was surely coming, considering six, now seven, children would have wandered into the Underground only to never be seen again.

And Asgore himself had, in fact, declared war on the humans. It was rash, it was a decision borne of anger and despair at having lost two children in one night, and it was a decision that ended up being key to the morale of the monsters being restored. It was necessary. The deaths of the children following that were necessary. Seven lives for the lives of thousands.

But now? It had been so long since the last child fell that most monsters didn't even know what a human looked like (luckily for the human currently wandering around unchecked).

"We will cross that bridge when - and if - we get to it," Asgore said. "Until then, we must find the human, and make sure we know where it is. Make sure the monsters are safe. Let it come to me, and I will strike the final blow. Your jobs, until then, are clear. Guide the human, keep the Underground safe should it try anything. We will reconvene in New Home, when the time comes."

"Do you think it poses a threat?" Alphys asked.

"no," Sans supplied. "not this time."

Vague as ever, but then, no one expected anything else out of Sans. Only Asgore knew why he was here at all. He accepted the answer with a solemn nod.

"There must be another way," Alphys spoke up again, nervously pushing her glasses up the bridge of her nose. Her hand was visibly shaking as she did so.

He wished there was. Truly. "There isn't. We only need one more SOUL to break the barrier and reach freedom. We need to do this, and you know that."

If they didn't, then the sacrifice of the others will have been in vain. They had to do this. Asgore wasn't sure if he wasn't trying to convince himself of that as much as he was trying to convince Alphys.

She sniffled. "I don't want to use the machine again," she said, and it was very nearly a whisper, not meant for anyone's ears, but reaching them anyway.

"You must." Asgore was firm. He was resolute. He could not risk showing a single crack in his resolve, or everything would fall apart. Inside him, a storm raged. He felt sick. Alphys looked sick.

"There has to be another way," she repeated quietly, eyes downcast. She adjusted her glasses with an obviously shaking hand. But there wasn't another way - they'd spent two decades trying to find another way, and there simply... wasn't. The barrier would only yield to seven human SOULs, nothing more, nothing less, and this was the only way to acquire them; sacrificing monsterkind as a whole was not an option.

Asgore sighed, the weariness of decades past on his shoulders. "If you can find a way," he said, "Then I would be most grateful to you. If you cannot, then we will proceed with the plan." He turned to face the others. "I do not want any unnecessary bloodshed, nor do I want any unnecessary loss of life or SOUL, be it monster... or human. Circumstance has left us with little choice in that regard. I trust that I need not remind you of our predicament, and I lament that it comes down to us versus them. We have no other choice."

"We could just... stay. Here." Alphys said, still so quiet Asgore had to strain to hear her. She'd gone beet-red before she even finished the sentence. "... I mean, we've... we've been here this long right?"

"Then the sacrifice of the other six human SOULs will have been in vain, and we will be trapped here for eternity," Asgore reminded her, allowing a bit of gentleness to bleed into his otherwise stern tone. "If you can find another way, you are welcome to. Until then, we follow the plan as we have done for the previous humans."

With that, he rose to his feet, watching the others do the same in response with their heads lowered in respect. The conversation was over. There was to be no further debate.

"Well then. You all have your orders. The child should be in Waterfall now," he turned to face Undyne, who nodded in wordless understanding. It was up to her to capture the child or guide it further toward New Home. "Keep me updated on the happenings. Do not let any monsters come to harm, if you can at all prevent it."

Undyne inclined her head, taking hold of her spear. It caught the sparse unnatural light of the roundtable chamber, glinting like rubies (or fresh blood, his mind supplied, sending a shudder down his spine.)

"You are all dismissed," Asgore said with a nod to show his appreciation.

Alphys was first out of the room with surprising speed. Understandable. She was a gentle soul, a young soul, and none of this had been particularly easy on her. Asgore knew the SOULs of the six others rested heavily on her conscience. He wished he could take that burden from her - it was, after all, his orders that led to the creation of the DT Extraction Machine. To the deaths. It was necessary, he reminded himself. All of this was necessary, for monsterkind as a whole.

Wasn't it?

Undyne shot him a glance, a raised eyebrow. I hope you know what you're doing, it said. He didn't. He threw her a solemn smile in return anyway, and it seemed to satisfy her for now; she stalked out of the room, her armor rattling loudly in the otherwise oppressively silent room.

Sans remained. For a long time, they were both silent, stood around the empty and too-large table, in the too-large room meant for more than just their sad five-soul crisis meeting.

There were supposed to be more here.

Something was wrong.

Someone was missing.

How could he forget?

"you feel it too?" Sans asked, finally breaking the silence. Asgore almost wished he hadn't. "he's back."

He's back. Who was back? Who left? Asgore felt like he'd been punched square in the chest, forcing air out of his lungs, keeping it out, his throat was too tight. The room seemed to spin. He was back. He was gone. He was missing.

Who was he?

"Who?" he dared to ask.

"you know who."

He didn't, though he knew it was something he absolutely should know. It was on the tip of his tongue, always evading his grasp, flitting just out of reach. He really was forgetting something. Something important. Someone important.

"We have more pressing concerns at the moment," Asgore said. The human took first priority for now, though he would be lying if he said that he didn't feel like something was horribly wrong. "Keep an eye on the human. You know what you have to do."

"could be dangerous. been a while since he was around."

The pronoun game was really starting to wear on Asgore's patience, frustration bubbled in his lungs and coiled in his muscles, but he still dared not ask who on earth he was forgetting for a second time. Admitting that he didn't know who he was felt more dangerous than carrying on the endless game of pretending he knew what he was doing. Like forgetting an in-laws name. Except with much higher stakes.

"We will deal with him when and if it becomes relevant. We have more pressing concerns," he repeated firmly.

For a long time, Sans said nothing, studying Asgore through white pinprick pupils in a sea of black. Eyes that suddenly felt unsettlingly familiar, and not just because of Papyrus. There wasn't a doubt in Asgore's mind that Sans saw straight through him, but that, too, was a concern for another day.

"fine," Sans said finally, and rose to his feet with a dramatic groan and exaggerated stretch. "don't say i didn't warn ya."

Asgore dipped his head, a thank you, please leave going unsaid. Sans took the hint and, with a casual two-finger salute, shuffled out of the room, pointedly leaving the door ajar.

Spirits.

With a long sigh of his own, Asgore rubbed his face, hefted his trident, and made off toward the throne room.