A Regressor's Bucket List

Creak—

As Sejong lightly pushed the door open, a geometric structure was glowing in the center of a vast cavern.

The structure emitted a mysterious light, somewhere between blue and white, and possessed a form that seemed strangely familiar.

In the center was a massive sphere, and on the outside, circular bands of varying sizes layered together, encircling the sphere.

Woooong—

It looked almost like the orbits of electrons revolving around an atom.

Of course, the scale was vastly different, and instead of electrons moving along the orbits, there were circular bands.

The most distinct difference was that these bands were densely packed with unrecognizable characters. However, it was a structure that anyone who had studied during their school years would find familiar.

And that structure was...

"This is the essence that contains the core technology of Joseon."

It was the pivot that allowed this massive Floating Territory to stay suspended in the sky, and the power engine that established the system of utilizing mana known as 'Arts (Sulbeop).'

It was the pride of Joseon, corresponding to the Order's 'Central Satellite Magic Device.' As Sejong introduced it himself, this mana power hub concentrated the technology of the Floating Territory that had been developed over hundreds of years.

Naturally, unless one understood 'Arts (Sulbeop),' the Floating Territory’s unique magic system, they wouldn't even be able to guess the meaning of the characters packed onto those circular bands. But U-jin knew a little bit.

It wasn't that U-jin understood 'Arts (Sulbeop)' himself, but rather that he remembered the hint Kim Satgat had given him during the first round.

『...Just as a magic circle cannot be used simply because one knows how to draw the lines, Arts (Sulbeop) cannot be used simply because one can draw the characters.』

『......』

『The width of the stroke, the length, the tilt, the thickness, the mental imagery, the speed, the shading—every element existing in that moment must be imbued. Mana, by its nature, resembles a living creature.』

『......』

『...That is why it is so great. Not only creating those countless strokes but fitting them together like a puzzle... that is something no one but His Majesty could achieve.』

This was the first time U-jin had seen 'it' in person, including both the first round and his current life, but he had a rough idea of how incredible it was.

『Furthermore, it’s not just about the characters; even their positions contain the principles of all things in heaven and earth.』

『......』

『The rings, divided into three parts from the outside—the Yughabui (Instrument of Six Harmonies), the Samjinui (Instrument of Three Luminaries), and the Sayuui (Instrument of Four Journeys)—all contain the mysteries of the celestial bodies. The characters engraved upon them also hold the six cardinal directions and the movements of the sun, moon, and stars. It is not something easily understood by an ordinary mind.』

Of course, he hadn't fully understood Kim Satgat's explanation back then.

He only roughly grasped that because it was manufactured by placing characters in 'optimal' positions while considering countless factors, it required a level of precision and understanding that an average person couldn't even dream of.

And because of that, the impossible feat of creating a new type of mana power hub had been achieved.

Ahem—

"Listen well, for I shall not explain this twice."

...If U-jin, who had only heard about it, felt this way, how much more so for Sejong?

Sejong had watched and remembered every step of the process from the very beginning.

Even if no one else knew, he was one of the people who understood the significance of that structure best.

The voice of Sejong as he cleared his throat was now laced with uncontrollable joy.

The word 'doting' naturally came to mind.

With his lips twitching, unable to wait to show this off, he looked less like a monarch and more like an inventor who had just unveiled his creation to the world, or a father explaining his newborn baby.

The dignity of centuries of experience that had been exuded just a moment ago had vanished without a trace.

And so, gathering all that doting energy, Sejong began to explain the massive structure.

"This object is the Honcheon..."

Or rather, he tried to.

Clang—!

A hammer flew from somewhere and landed in front of Sejong, followed by a gruff voice.

"Hey! Didn't I tell ya not to give it such a shitty name!"

Despite the sudden appearance of a third party, U-jin didn't bother to turn his head.

The reason was simple.

Even without seeing the face, he knew who the owner of that voice was.

There was only one person here who would dare to use such crude language toward Sejong, the ruler of the Floating Territory.

The friend who had been with Sejong since he first ascended to the Upper Plane, and a core figure of 'Floating Specter Joseon' who had perhaps contributed more to this 'Floating Territory' than Sejong himself.

At the same time, he was the person who had invented this massive mana hub and completed the new mana utilization system called 'Arts (Sulbeop).'

"It's an Arc Reactor! An Arc Reactor!"

It was 'Jang Yeong-sil.'

* * *

Jang Yeong-sil.

The number one figure that came to mind when thinking of 'Sejong's recruitment of talent,' and a genius representing Joseon.

A scientist, engineer, and astronomer born as the child of a government slave in Dongnae-hyeon, Gyeongsang (modern-day Busan).

Despite his slave origins, he was appointed to official positions and became a world-class technologist who created numerous inventions representing Joseon.

"Honcheon Sulbeop Power Source, my foot... Just what kind of shitty, ancient name are you trying to stick on it now?"

"Ahem."

"I'm the only one who'd understand that. Even if you list those disgusting words to a snot-nosed brat, he won't understand a lick of it."

Unlike the birth and death years of 'Sejong,' which were clearly recorded in the Annals of the Joseon Dynasty, Jang Yeong-sil's years were uncertain from the start.

While his origin in Dongnae and his status as a government slave were clearly recorded, the specific names of his parents were not.

Regarding his later years, although it was recorded that he rose to positions like the Deputy Director of the Royal Wardrobe, there was no clear date of his death.

In particular, concerning those ambiguous final years, there was a record of him being flogged and dismissed after a palanquin he built for Sejong broke. After that, there were no records at all.

Where he went, what he did, how long he lived, whether he was reinstated or remained dismissed—none of it could be found in any record.

And the reason, of course, was standing right before them.

"Arc Re-ac-tor. See how sophisticated and crisp it sounds?"

"......"

"Right?"

It was because he had undergone Dimensional Transcendence to the Upper Plane along with Sejong.

Surprisingly, the special relationship between King Sejong the Great and the inventor Jang Yeong-sil from the Lower-Dimensional Plane was still continuing in the Upper Plane.

However, if there was one difference from the Lower-Dimensional Plane...

"...The two of you are much more informal than I expected."

"Don't you know the 'Loyalty between King and Subject'?."

"......"

"I'm over six hundred years old and my memory's fading, but that 'informality' ended back in the Lower World."

It was that the gap between the two, which would have been that of a King and a subject, had almost entirely vanished.

As evidenced by the hammer he had thrown upon his entrance, Jang Yeong-sil showed no etiquette whatsoever toward Sejong.

Truly, not even a shred of it.

"Ahem..."

Sejong's uncomfortable coughing suggested that he hadn't entirely consented to this, but seeing as he didn't strongly refute it, there seemed to be a reason.

"...Still, he's the one who freed you from being a slave."

U-jin cautiously offered a different opinion on their 'Loyalty between King and Subject' and took Sejong's side, but Jang Yeong-sil barked back in disgust.

"Freed, my foot. I just went from being a government slave to being this guy's private slave."

"......"

"It was better when I was a government slave in Dongnae. At least I could sleep back then. I was an idiot to follow him just because he offered me a rank. Now I can't even sleep properly and I'm still being worked to the bone. Can't you see?"

"......"

He spoke that way, but as he had mentioned, their bond had lasted for 600 years.

If he truly hated it enough to be that disgusted, he would have run away long ago.

The fact that he remained by Sejong's side without leaving the Floating Territory meant that while his attitude was rough, his heart was aligned with Sejong's.

In fact, the Floating Territory was built by Sejong gathering talent and Jang Yeong-sil leading them.

And the 'Arc Reactor' before them was the result of Sejong’s concept and Jang Yeong-sil’s design and completion.

"Since you're here, why don't you explain it yourself? I was just about to explain this Honcheon..."

"Arc Reactor."

"...The Arc Reactor. You know more about it than I do, don't you?"

"Forget it. What's the point of explaining? He won't understand it anyway."

Swish—

Picking up the hammer he had thrown on the ground, Jang Yeong-sil suddenly held it out toward Sejong and asked.

"And... didn't I tell you to temporarily reconstruct this for the input method of the Order's 'Central Satellite Magic Device'?"

Flinch—

"...I did relay that message."

"If you're gonna do it, I'll explain."

"......"

At Jang Yeong-sil's words, Sejong flinched and took a step back.

"Do you think changing the input method is as easy as naming a dog?"

"......"

"I have to engrave new intaglios inside the Sayuui (Instrument of Four Journeys) and even drive in the rings. Are you gonna do it? Are you?!"

As Jang Yeong-sil shrieked, Sejong turned his head and closed his eyes as if he were used to it.

He waved his hand with a cough.

"...I ask this of you, my friend."

"Friend, my ass."

Leaving behind that short remark, he turned back toward the Arc Reactor.

After the storm had passed, Sejong wiped away some cold sweat and turned to U-jin with a hollow laugh.

Hoho—

"He’s naturally a bit impatient and has a very rough personality. He gave me quite a hard time in the Lower World because of that as well."

"......"

"I shall explain it myself."

Sejong’s subsequent explanation was rather cliché.

"...Thus, it produces an enormous amount of output relative to its size, but unlike common sense, it has a marvelous and efficient structure that directly converts reactive substances into mana for supply."

Of course, for someone encountering this 'Arc Reactor' for the very first time, it was content that could be found interesting.

"...It emits no pollutants, so it is free from the risk of accidents, and in terms of stability..."

However, while it was U-jin's first time seeing it in person, it wasn't as if he didn't know of its existence.

Since he already knew how great it was and its general principles, he simply listened while nodding; his curiosity wasn't particularly piqued.

And at the end of Sejong’s explanation...

"...So. Do you feel like joining us now?"

The same question sat there once again.