Chapter Text

The barrier fizzled and sealed itself around the cave entrance with a hiss like fading lightning. The cave echoed with screams and cries. Monsters ran through the darkness searching for loved ones or sat crying as they tended to the wounded. Some of them were already beating fists or claws or tentacles against the barrier in helpless denial. They had lost…everything. Thousands of lives, and now their whole world. Trees, the oceans, the sun. All gone. They were trapped, sealed underground forever.

W.D. Gaster stood quiet among the chaos around him, watching the barrier with measured calm. He couldn’t keep his hands from shaking, but the rest of him was still. He needed to think. There wasn’t time for panic or grief. He needed to study the barrier now, before the humans on the other side buried the cave’s entrance. He might never have a chance to see it again. Still trembling, he reached into a pocket for his notebook and began to take notes. Eerie, pulsing light filtered through the barrier.

Seven humans had cast this spell. Seven souls. The power of the human soul was truly incredible.

“Gaster? Gaster! Oh, thank goodness!”

He blinked hard and looked up, but didn’t stop writing. He had always been good at moving his hands without needing to think about it.

King Asgore rushed toward him, Queen Toriel close behind. Asgore looked stricken; Toriel’s face was unreadable. The king clapped his hands on Gaster’s shoulders.

“Thank goodness you’re alright. I thought for sure—earlier, when you stayed behind in your laboratory…”

Gaster answered. There was the familiar hesitation on Asgore’s face as the king had to mentally translate what Gaster was saying. Gaster didn’t speak like any other monster alive. The king and queen were some of the few monsters who could understand his speech.

“I made it just in time. Unfortunately, I wasn’t fast enough to gather any of my equipment. I shall have to start from scratch.”

“I am just glad you’re safe, old friend.” The relief in Asgore’s voice was painful to hear. “What about your family? Did they ma—”

“That is not important right now.” Gaster’s hands shook, but he kept writing. There was no time. The light was already starting to fade as the humans buried the entrance. He gestured at the barrier, at the last glimpse of filtered light.

“Something needs to be done about that.”

***

Asgore named the blossoming city “Home.” He had never been good at naming things.

They built within the first cavern they could find, not far from where the cave’s entrance had been. The cavern was small. Eventually, the monsters would have to make their way deeper underground, find other caverns large enough to support the population.

For now, the numbers were still small. So few of them left. But it had been years now, and they were rebuilding, repopulating. Monsters could be resilient when they put their minds to it.

Resilience was a powerful thing. Gaster had been thinking about that a lot, lately.

“I think it’s high time we had an official science division,” Asgore said to him one day. They stood on a parapet overlooking the small city. “A team of brilliant minds to devote themselves to helping monsters adapt to our new lifestyles. To study the underground—and to begin to try and find a way out of it.”

Asgore’s eyes met Gaster’s. Not many people liked to look Gaster in the eye; he thought it must be because they found his stare…unsettling. Asgore was either too kind or too naïve to really notice. Probably both.

“I want you to lead it. I want you to be my Royal Scientist, in charge of the entire science division.”

“Me, Your Majesty?”

Asgore chuckled. “Who else? You’re the most brilliant of those brilliant minds I mentioned.”

It was true. That wasn’t ego; it was simple fact.

“You’d have all the resources you could need. A team. I’d only ask that you keep me up to speed on what you’re working on.” Asgore elbowed him lightly. “And come by for dinner once in awhile. We never see you anymore—Tori keeps asking about you.”

Gaster smiled faintly. “I am sorry, King Asgore. I have been so busy lately. I would be honored to lead the science division. And…of course, I would be delighted to spend more time with you and the queen.”

A team. A true lab, not the makeshift one he ran in his basement. The resources to finally, maybe, make progress on his study of the barrier and its relation to souls. He had been at a standstill these last few years, making the same notes and taking the same measurements over and over.

He and the king shook hands.

“Excellent! I had a feeling you would agree,” Asgore said with a wink. Gaster noticed for the first time that the king was starting to grow a beard.

Asgore slung an arm around Gaster’s narrow shoulders and steered him back toward the castle.

“Why don’t we discuss the details over tea? Tori discovered that you can make a tea out of those golden flowers you find growing down here. It’s positively delicious. And you can tell me about what projects you look forward to working on.”

“I have far too many ideas. I fear most of them would bore you.” Gaster smiled again. He hadn’t smiled this much in years. “But I do have one rather exciting project that I’ve been working with on paper. Monster society will need a source of power here in the underground. If we can’t utilize the wind or sun anymore, then…our energy will have to come from below. Geothermal power. Of course, we will need some kind of machine to extract it. Something massive…”

***

The cavern became cramped sooner than anyone could have predicted. Within only a few decades, monsters were starting to trickle out of Home in search of a better place to settle. Questing parties had found a chilly cavern not far from Home; and beyond that, a massive network of rivers and waterfalls. The caverns only grew larger the deeper the monsters travelled.

After the first trickles came the flood. Soon there was a mass exodus out of Home, with the king and queen leading the way. Gaster and his scientists went with them. The old city was nearly empty in a matter of months, and the long journey through the dark began.

Gaster never missed Home even once.

On such a long journey, it stood to reason that a sort of religion began to spring up. Gaster began to overhear monsters speaking off a “prophecy” concerning the old Delta Rune. They said that someday, someone would descend from the world above to free the monsters from the underground—in one way or another. Hogwash, as far as Gaster was concerned. He had more important things to think about than silly prophecies. According to some of the more industrious monsters who had gone on ahead, there was a place beyond the waterfalls where the earth opened up. Where the fiery heart of the world was exposed. If the rumors were true, it was the perfect place to build his power station. His…Core.

***

“Phew, it really is hot here, isn’t it?” Asgore was saying, tugging at the collar of his robe. “And not a flower in sight. We should call this place…hot…Hot Place. Lava…Level? Hm. Hot…lands?”

Gaster nodded vaguely, not really paying attention. He was surveying the area, taking in the vast, vast amounts of magma that coursed through the earth only a few hundred feet below them all. Everything was cast in an orange glow.

“Yes, ah…that last one, I think, that would work…”

Asgore fanned himself. “Some of the monsters are saying that there is a massive cavern a few miles ahead that should serve us all well. Beyond that, well, it seems they’ve found another edge of the barrier.” Asgore smiled a little sadly. “It seems our journey is at last almost over.”

Gaster turned to look at him.

“I think I will stay here. Some monsters have already started to build a settlement. This place will be perfect for my Core plan. I think it is best if I build the science division’s laboratory nearby, so we can directly monitor the construction and activation of the Core.”

It would take years to build the thing, and Gaster needed to be there for every single step of the process. There were certain…aspects to the Core that he particularly needed to supervise. When it was finished, it was going to be so much more than just a power station. But the king didn’t need to know that just yet. Even Gaster still wasn’t certain about how to do what he truly wanted to do.

Asgore looked rather pained at the news.

“I had a feeling this was coming,” he said. “You don’t want to at least accompany us? See the other end of the barrier?”

A large part of Gaster never wanted to see the barrier again. But the scientist in him knew that he had to. He gave the king’s shoulder a squeeze.

“I will visit you in your new home. I promise.”

Later, Gaster watched until the king, queen, and the thousands of monsters following them were out of sight. Then he turned to his science team.

“Well, no sense in dawdling. We have a lot of work to do.”