The mission Fujimoto Tōma had just completed was a routine commission in the Land of Rivers. Nothing difficult.
A-rank and S-rank missions sounded intimidating, mostly because people remembered spectacles like Zabuza clashing with Kakashi. In reality, most high-level missions were only dangerous when information was wrong or when there were civilians to protect. Even the Land of Waves disaster would have gone very differently if the intel had been accurate and Kakashi had not been constrained.
For shinobi, at least before truly absurd individuals started appearing, information mattered more than raw danger.
For Tōma, the mission itself was irrelevant. He had finished it easily.
What mattered was something he had felt while he was there.
Natural energy. Vast. Dense. Abnormally so.
At the time, he had been on duty and needed to return to report, so he had not stayed behind to investigate. Now, with the mission complete and Tsunade having effectively given him extended leave, it was time to go back.
Natural energy was critical to him.
The modification of his body had slowed to a crawl. Slower every day. At this rate, he genuinely wondered if he would finish before the Ōtsutsuki ever appeared.
He knew the reason. The natural energy density of the world was simply too low.
If it were higher, the process would still be slow, but not like this.
Sometimes, Tōma could not help feeling unlucky. If he had been born before the Divine Tree drained the world dry, this would not be an issue. But now, most of the planet's natural energy had already been consumed, leaving behind only scraps.
Scraps were not enough.
That was why the massive concentration he had sensed in the Land of Rivers mattered so much.
Perhaps even Naruto's Sage Mode limitation had something to do with this, he thought briefly. Five minutes of power, preceded by long absorption times. The world itself simply did not have enough natural energy to spare.
There was no way to confirm it, so he let the thought go.
In the next moment, Tōma vanished.
He had left a Flying Thunder God marker behind during the mission.
He reappeared near the coastline of the Land of Rivers.
Following the faint pull of his senses, Tōma moved inland, the natural energy growing clearer with every step. His smile widened.
He had not imagined it. This quantity was abnormal. How it had survived until now did not matter. The fact that it had was enough.
Soon, he reached a dead end.
A stone door blocked the path, its surface carved with unfamiliar patterns. Mechanisms. Traps.
So that was how it had been preserved.
Tōma stared at it for a moment, then sighed.
He had no intention of solving puzzles or searching for someone who understood ancient mechanisms.
He drew the Inkshadow Blade.
One clean swing.
The sword cut through stone as easily as slicing tofu. The mechanisms shattered, useless against raw force. Moments later, he stepped inside.
What greeted him made him pause.
The underground space was enormous. Far larger than expected. A ruin, ancient and deep, stretching downward beyond sight.
Tōma searched his memory of the original story.
Nothing.
A structure this large should have appeared somewhere. And yet, there was no trace of it in his recollection.
Either he had missed it entirely, or this place had never been mentioned.
He stopped thinking about it.
Whether it was known or unknown did not matter. The natural energy did.
Ignoring the remnants of traps and mechanisms, Tōma advanced directly. Walls were cut apart. Gaps were crossed by manipulating magnetic fields to float through the air. He did not bother with finesse.
Eventually, he reached what looked like a central hall.
The natural energy he sensed was directly above.
Only then did he slow down.
He examined the surroundings and frowned. There was something here. Not a standard sealing array. And on a nearby island-like platform, a massive, intricate pattern was carved into the stone.
It did not resemble any fuinjutsu he knew.
Tōma looked up at the ancient ruin, at the overwhelming natural energy overhead, and a thought formed.
This place likely predated shinobi entirely.
Whatever power system this was, it existed before chakra-based techniques.
That alone made it invaluable.
He summoned paper and pen and carefully copied the entire pattern, committing every line to record. Whatever it was, he could study it later, after his body modification was complete.
Nearby, he found what appeared to be a switch. Presumably meant to open the final chamber. Something was missing. Without it, the mechanism was inert.
He did not try to force it.
With this much natural energy involved, brute force at the final stage was too risky. Destroying it by accident would be unforgivable.
Then a different thought struck him.
If this was not a shinobi-style seal, would it even respond to ninjutsu defenses?
Worth testing.
Tōma formed hand seals slowly. Awkwardly.
Earth Release.
He almost never used it. Without the attribute affinity, training it was inefficient. Still, he knew the basics. The power was terrible, but that did not matter.
His body sank into the ground, and he "swam" forward through the earth toward the source.
No resistance.
None at all.
When he emerged, Tōma froze.
Before him was a lake.
A glowing, emerald lake.
Liquid natural energy.
For a moment, he simply stared. Then understanding clicked.
This was not energy condensed from the air.
It was a vein.
A mineral deposit infused with natural energy.
That explained everything. The Divine Tree had drained ambient energy first. Deposits like this had either been overlooked or never reached before Kaguya consumed the chakra fruit.
The details were irrelevant.
What mattered was this.
His natural energy problem was solved.
Tōma sat down at the edge of the lake, closed his eyes, and began absorbing.
Green light rose from the surface, flowing toward him in visible streams. Almost immediately, his body reacted. A familiar sensation returned.
Soreness. Tingling. Rapid reconstruction.
He had only felt this once before, at the very beginning.
This time, it was stronger. And strangely comfortable.
When he finally opened his eyes, a long time had passed.
The effect of this session alone rivaled days of previous effort.
And the lake had barely diminished.
Tōma exhaled slowly, excitement burning in his eyes.
Still, he stopped.
His body was already reaching its limit. Pushing further would be counterproductive. Even with a lake like this, the process would take time.
And something else bothered him.
This amount of natural energy was excessive. Abnormal. His modification process might not be entirely… standard.
That was a problem for later.
As he stood, a faint mark briefly surfaced on his forehead. The same mark that once existed only on his soul.
Tōma did not notice.
He planted a Flying Thunder God kunai nearby, then layered simple detection seals throughout the ruins. Weak, but sufficient. If anyone entered, he would know.
If this place was disturbed, everything would collapse.
Only after finishing did he return to Konoha.
Satisfied.