— The Philosopher's Stone!
This object exists in many Western mythical worlds. Its essence and function differ completely across different worlds.
In some worlds, the Philosopher's Stone is merely a rare and precious metal. In others, it's an elixir of immortality. In yet others, it's a wish-granting device... In short, while the essence and function vary entirely, one point remains similar.
It consistently represents the pinnacle of alchemy in its respective world.
Ryuji possesses three Philosopher's Stones, each different.
The one he intends to use now is an ultimate metal from a certain Western fantasy world: the Universal Gold.
Its function is to substitute for the properties of any metal.
Of course, the term 'any' is relative to the world it belongs to.
Ryuji once attempted to have the Philosopher's Stone substitute for the ten great metals from the Marvel Comics Universe but failed.
Nevertheless, it remains a powerful treasure, capable of substituting for even the core material required to forge the Ugo Ring.
Noting the use of 'even' here, one should understand this core material is extremely precious.
To understand the Ugo Ring, one must first know the origin of the 'Book of Raziel'.
Actually, this book also existed in Ryuji's previous life.
In Solomon's myths and legends, the Archangel Raziel bestowed upon King Solomon a magical book capable of summoning and controlling spirits and demons.
That book was the 'Book of Raziel'.
Of course, the "Book of Raziel" Ryuji obtained through check-in wasn't from the Solomon myths of his previous life but from a similar world born from that prototype.
Ryuji's 'Book of Raziel' was also a magical book bestowed upon King Solomon by a deity, but it recorded not the summoning and controlling of spirits and demons, but their creation.
And Ugo was a Demon God created by King Solomon in that world.
He was not among the seventy-two pillars but was nobler and more powerful than them. His origins were extraordinary; he was not created by King Solomon from scratch.
Instead, he was transformed from another being.
His identity was one of the three Magi under Solomon's command, the world-creating magician, also the Child of God.
And the Ugo Ring was the alchemical tool he used when creating the world's earth to prevent its collapse.
Here, we should mention alchemy. In some worlds, alchemy is similar to magic.
But in other worlds, it encompasses a broad body of knowledge involving chemistry, physics, materials, mysticism, and other disciplines… a technology that allows the creation of various miraculous items through knowledge alone, without special abilities.
The Ugo Ring belongs to the latter type of alchemical item, producible simply through the application of knowledge.
However, that world and this one are different.
Especially regarding the core magical energy called 'Rukh', which doesn't exist here at all.
Although Chakra can achieve things Rukh could, the reactions produced by combining various substances are completely different.
Therefore, Ryuji could only use the Philosopher's Stone as a substitute.
After all, the Ugo Ring's core material is a magic-imbued mineral core. In that world's mysticism, it represented the earth's core, the world's origin, etc.
The Mechanical City Ryuji designed was to be a flying sky city, so the foundation was particularly important.
Generally, for maintaining flight, reinforcing rock hardness using Ninjutsu would suffice.
But Ryuji considered wartime scenarios where enemies might try to destroy the city by attacking its foundation. Hence, the foundation needed to be exceptionally solid and sturdy.
Initially, he considered forging a platform from rare metals and building the city upon it.
But considering funding and the immovable Dragon Vein, he changed the plan to excavate the earth bearing the Dragon Vein along with the city, then use the Ugo Ring to stabilize it, transforming the uplifted rock layer into a continental plate.
This would maintain the city foundation's vitality and thickness/hardness, solving both foundational defense and the immovable Dragon Vein problem.
In the future, the city's agricultural zones could also support farming.
After all, although small in area, this would undoubtedly be a continental plate equivalent to those of the world.
Regarding defense... Unless possessing the ability to destroy a continental plate, one shouldn't consider attacking the foundation.
As for duration... The Ugo Ring is a ten-meter-diameter ring. At its center is a magic circle combining a regular and inverted hexagram, requiring a mineral core as its energy source at the circle's heart.
The mineral core contains immense magical power. Amplified by the magic circle, it's sufficient to support the world.
And the magic crystal core's energy originates from the earth.
Ugo used a magic crystal core as the Ugo Ring's core to support the earth, making it the earth's core. The earth would continuously feed energy back into the core, creating an infinite cycle… a closed loop.
This is also why terms like 'eternal', 'infinite', etc., are frequently mentioned in the book.
Achieving this effect could, in a sense, be considered eternal.
Of course, Ryuji's Ugo Ring, substituted with the Philosopher's Stone, isn't that powerful. The earth area it can support is limited.
Otherwise, he could directly use it to improve the Land of Wind's geology. Why bother building a Mechanical City?
Additionally, the regular and inverted hexagram circle must be drawn in a single stroke to be effective. Ordinary people cannot do this; only a world-creating magician can.
Ryuji cannot either; he needs to use the 3D printer.
Not just the hexagram circle, but processing materials like the Philosopher's Stone, secondary Adamantium, and Vibranium also requires the 3D printer.
Therefore, Ryuji planned to return to Sunagakure, also to observe the specific negotiation process between Sunagakure and Konoha.
The next day.
Ryuji packed his belongings. Before leaving, he gave final instructions to Ebizo. "Ebizo-senpai, you can start arranging personnel to excavate the foundation. It's fine if the area is larger; we might expand later. But it absolutely cannot be smaller."
"Don't worry about that. Although I'm old, I'm not senile yet. I understand these basics."
"Then I leave this place to you."
"Alright!"
Thus, Ryuji left Roran, taking the two prisoners, Shibi and Choza.
...
The world doesn't revolve around a single individual.
During this period, besides Ryuji focusing on construction, other places and forces also took action.
Let's rewind thirteen days, to the fifth day after Ryuji successfully defeated the Konoha's team and secured the Dragon Vein.
Konoha, Hokage's Office.
"...To think even you were no match."
After listening to Minato's mission report, Hiruzen's expression turned grave. He even forgot to inhale from the pipe in his mouth, merely holding it there.
This was understandable; the news Minato brought was too serious.
Originally, he worried that when the four-village alliance attacked Konoha, Sunagakure would take advantage and attack as well.
Now, Konoha lost two Elite Jonin, while Sunagakure gained the Dragon Vein, greatly boosting their power. Their ambitions would likely swell further.
Making Sunagakure refrain from acting when Konoha was in trouble would probably be even more difficult.
Especially that Senki Ryuji. Even a team led by Minato was no match for him. His strength had been severely underestimated.
(A/N: This 'Book of Raziel' is not from the protagonist's previous life's myths, nor from Magi. It's the author's original creation, something I make up randomly.
Originally, it was set to be from 'Magi', but the later worldview and power system in Magi became too overpowered. Sinbad and David vied for the title of Sacred Palace Master, casually destroying universes.
Alibaba, relying on Amon's Metal Vessel, fought Sinbad to a standstill.
The background character King Solomon, before dying, created a universe with a mere thought. During his life, he severed the gods' manipulation of fate over all living beings.
When I was outlining, I had only seen the anime, not the manga parts, so...
In short, that's the situation. If I continued setting it as King Solomon's magic book from the Magi world, the power system would collapse.
Now, the foundation here is essentially a miniature, essence of continental plate. Only by possessing the ability to sink a continent could this foundation be destroyed.)