Shin had long suspected that the core inside the moon was the Demonic Statue of the Outer Path.
Such a vast place—with a miniature sun in the sky, forests and rivers below—required energy to sustain it all.
And the Demonic Statue of the Outer Path solved that problem perfectly.
It seemed that after Hamura arrived on the moon, he had begun making preparations in this regard. On one hand, he used Sealing Technique to seal the Demonic Statue of the Outer Path; on the other, he used it as the energy source within the moon.
In essence, the Demonic Statue of the Outer Path was the shell of the Ten-Tails. Though all its chakra had been extracted to form the One-Tails through Nine-Tails, even an empty shell still possessed the greatest vitality and an unimaginable amount of chakra.
The Ten-Tails itself was the origin of chakra. Even as a shell, it continuously generated chakra without end.
It was merely that, without the Tailed Beasts within it, this chakra could not be preserved for long. Hamura had made use of this point, turning the Ten-Tails' shell into a perpetual generator.
In the original story, when Naruto Uzumaki and the others entered the moon, they had also seen a small artificial moon, vast forests, and even abandoned villages. Though its interior was dilapidated, it still retained an appearance not too different from the Main World.
However, by then, the Demonic Statue of the Outer Path had long since left the moon, and even the Fourth Shinobi World War had ended. The source of energy at the time was the Giant Tenseigan, formed from a massive collection of Byakugan.
Of course, in this world, because the main and branch families still existed, that Giant Tenseigan had yet to appear. If events had proceeded