For a long time, Gaster simply leans over the central control panels, flipping switches and hitting buttons. You and Alphys share a glance every now and again, but neither of you really know what he's doing.

And then there's a spark. A purple spark of Magic, running along some sort of channel in the floor towards the big window, where it disappears into the octagonal room of the center of the CORE. You see it beyond the window, jumping along one of the thin, gossamer cables, until it hits the wall, disappearing into the node from which the cable runs.

And then it explodes outwards. A brilliant, vibrant wave of Magic, running out from that one node, jumping across every cable it touches to light another point on the wall of the huge room. And as the Magic ripples outward, you see that the etchings in the walls of the room are runes- not unlike the ones Gaster carved into you not so long ago to save your life. But while there were a few hundred on you, there must be thousands- no, millions covering the walls of the octagonal room, each lighting with Magic an instant after the one beside it, until the entire room is lit up, Magic arcing along the cables and flickering and pulsing on the walls.

And then you hear it. A muffled thwoom.... Thwoom.... Thwoom.... like the huge blade of a fan passing by, somewhere deep in the CORE. And it gets faster, louder, until it sounds not unlike the pounding footsteps of a person striding along. And there's a humming noise growing, too, throbbing in your ears like a deep bass beat.

You peel your eyes from the growing radiance in the center chamber and look back to Gaster.

He's not so much leaning over the control panels anymore, he's standing upright. And he's controlling the entire room. Everything he does, every button pressed, every switch flipped, every dial turned, is done with his summonable hands. With his normal hands, he's making wide and grand gestures, presumably controlling his summonable hands. But he looks like a conductor of some great orchestra, or... or it maybe even looks like he's dancing, pivoting in place, swaying just a little, sweeping his arms around, sharp twitches of the wrist and fingers sending his Magic flying.

And, to top it all off, his eyes are closed, and his expression is totally relaxed.

Watching him is... kind of mesmerizing, honestly. You can't look away. And as you watch, the sounds of the CORE growing and working their way into your brain, you realize that the Royal Scientist's precise, graceful movements aren't in the slightest bit out of synch with the great machine's music.

And then the light of the Magic in the heart of the CORE suddenly washes out from the purple of Gaster's Magic to a brilliant white, and the glow is so bright you can barely see, until one of Gaster's gestures brings down some sort of tinted glass cover over the window.

And from there, he calms down. Ish. He's still rocking a little on his toes, and that big grin is back, but he's not... dancing anymore.

"Right!" He says, clasping his hands together in front of him. "That's the main conductor unit on, but we've still got to check on the secondary unit, and check the containment and distribution units and backup flood tanks. Also have to get the cooling system online again, since that wolf isn't in Snowdin anymore. Come on, no time to waste!"

And with that, he's already out the door.

You and Alphys hurry along after him, but you come to an abrupt halt on stepping out the door. If you thought the CORE was impressive in the dark, you are utterly awestruck now. It's all catwalks and girders and tubes and pipes and wires and air ducts elevator shafts and now you can see that the entire thing wraps around the huge octagonal room, and everything, everything is moving. Machinery is shifting and humming, and the magma turbines are spinning so much faster now, and it seems certain intersections of the catwalks can rotate to connect other catwalks, and there are several huge, clear tubes in which you can see magma or water or concentrated liquid Magic rushing through, and there are so many lights, dials and gauges and monitors and so many others you don't know the names or purposes of, and-...

And it's like the whole thing is alive. Like it's living and breathing and it's got a heartbeat of its own.

And Gaster is on the move already. You have to run to catch up as he guides you and Alphys to an elevator, a different one than before. This one, you can actually see the whole elevator shaft, the bottom set on a foundation that plunged deep into the magma below, while the top is supported by thick cables connected to... somewhere far above.

Gaster ushers you into the elevator and pulls the gate closed- because it's one of those old-looking elevator doors where it's a collapsible gate for a door instead of a sliding door- and then he grabs a sort of emergency-brake looking lever and slams it to one side. The elevator lurches into motion and in moments you've arrived at your next destination, another catwalk, though this one is higher up, suspended from above by wires.

The second he's got the gate open, Gaster is striding- almost running- forward, each of his footfalls matching perfectly the pulse that echoes through the CORE. You and Alphys both have to hurry to keep up.

At some point- you're not entirely sure when, but at some point- the catwalk becomes a hallway, the walls lined with more switchboards and monitors, and Gaster has begun that mesmerizing dance again as you move down the hall, operating the machinery with ease.

And then you're coming into another huge chamber with magma at the bottom. It seems like it's almost an exact replica of the main chamber, just on a smaller scale, still with catwalks and cables spanning the entire thing, and a big octagonal pillar of a room right in the middle.

But instead of going into the control room, Gaster just flings open the door to be met with a brilliant white light.

"Look! It's already going! My autonomous startup system still works!" He seems exceptionally proud of that fact.

And then he's closing the door to the control room, and already striding away again, on to whatever system needs checking on next.

Eventually, after it seems you've run through the entire CORE, just barely managing to keep within arm's reach of the end of Gaster's coat flapping behind him, the three of you make it back to the main elevator, and Gaster takes you all back up to the part of the CORE that's open to the public. When the elevator doors open, you see Sans and Papyrus are already waiting there, apparently having already finished the puzzles.

"Well?" Gaster asks his taller son, face lit with an excited smile. "Did you enjoy the puzzles?"

"I did!" Papyrus exclaims. "And I didn't even need any help solving them!"

"Excellent! And you'll be glad to know that everything is still working just fine, and I've remembered what I came here for. We can start building the CORE 2.0 within the week!"

Everyone's excited about that.

There's a bit more talking, then you all turn to go.

"Wait!" Alphys suddenly calls. "D-Doctor, don't you need to shut the C-CORE down?"

"Nah," Gaster gestures dismissively. "When I turned it on, I set it to run itself out in a few hours. It'll shut itself down automatically just fine." He gets a kind of sad look on his face when he says that, and you can guess why.

But Alphys still has questions. "B-but when we all l-left the Underground, I h-had to shut it down so it wouldn't b-blow up. What's s-stopping it f-from doing that now?"

"Well, see," Gaster's voice shifts into that tone that Sans calls his Royal-Scientist-lecture-mode, "when the CORE was powering the whole Underground, it was set to just keep on producing Magic to power everything. And while there is a lot of extra measures to make sure it doesn't blow up, if it just kept on producing Magic without anything to use that Magic, eventually the buildup would become so great that it would rupture all the containment units and explode the CORE- though, if everything worked properly, it would probably take a good ten or fifteen years of the CORE just sitting there before it blew up. However, like I said, in turning it on now, I reset the reproduction loop to produce a much smaller amount of Magic in a much greater amount of time, so much so that it's using more Magic than it's producing, and in a few hours, it'll run itself dry and shut down." His mini-lecture over, Gaster sighs, his shoulders slumping a little. "It's a real shame, though. My third greatest creation just sitting down here, collecting dust. It was supposed to work for centuries."

"Well," Papyrus says with a grin, "we'll just have to make sure the new CORE is even better. On the surface, I'm sure it'll be used for a long time!"

Gaster just smiles and nods. "Right. Anyway, we should probably get going. It's probably dark outside already."

You all begin to leave again.

On the walk out, Gaster takes the lead, once more striding across that long blue catwalk, this time with the CORE lit up around him, and there's something about that image that burns itself into your brain. He walks with complete confidence, his coat billowing as the updrafts fill it with mist from below, and now his hands swing freely at his sides. And you can't shake the feeling that there's a new excitement in him, a new spark of life in his Soul.

§

A/N

Basically, if any of you were wondering what Gaster might be imagining the CORE music to sound like, or you just want something to listen to as you imagine Gaster running excitedly through a big huge machine, here's pretty much the whole playlist I was listening to as I wrote this chapter.

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Wow, that's a lot of the same one song.

But, of course, I still feel the need to say, if any of you have similarly epic CORE remixes, please do tell me!

Aaaaaanyway, thanks for reading, and I hope you enjoyed it! Comments and votes are my Favorite Things, and every notification I get makes my day!