Time passed swiftly. On a desolate plain, devoid of human presence, no one would have imagined that a hidden experimental base lay beneath.
Inside this base, corpses of all kinds were scattered everywhere.
There were ordinary animal corpses, as well as those of ninja beasts imbued with chakra.
Kurogane Ren stood among them, holding a thick stack of experimental data in his hands.
He had begun with fusion experiments between ordinary animals, then moved on to ninja beasts. Only after completing those stages did he proceed to higher-grade materials.
Even then, he started with fusions between ninja beasts and higher-grade materials. After all, while wild animals were plentiful in such a remote area, obtaining live high-grade materials was far more troublesome.
"The experimental data… there's a problem," Kurogane Ren muttered as he examined the records.
It wasn't that the fusions had failed. In fact, they had succeeded.
The issue lay in the post-fusion changes.
Although the fused subject had successfully gained the physique of a ninja beast, over time, subtle abnormalities began to appear. There were even signs of gradual collapse, though the process was slow.
Tapping his head thoughtfully, Kurogane Ren recalled details from the original story before finally uttering three words.
"Heaven, Earth, and Human."
Hiruko hadn't just gathered bloodline corpses—he had also prepared the optimal location and waited for a rare celestial phenomenon, a solar eclipse, before attempting the final fusion.
Perhaps it required harnessing natural energy during such astronomical changes.
But that was only necessary for fusing all five bloodline limits. The earlier fusions didn't require such extreme conditions.
"Then this must be the inherent flaw of the Demon Assimilation Technique," Kurogane Ren sighed.
He recalled how Hiruko's originally tall and sturdy physique had shrunk into that of a frail, almost androgynous youth after using the technique.
And how, after failing to fuse with Kakashi Hatake, he had become something neither human nor monster.
Kurogane Ren had long suspected there would be flaws. A technique like this could never be perfect.
Even if Hiruko had successfully met all three conditions—Heaven, Earth, and Human—and fused five bloodline limits, it would only reduce the flaws, not eliminate them entirely.
So, should he abandon the technique because of its defects?
A faint smile curled at Kurogane Ren's lips.
Impossible.
Without it, his current limitations were far worse.
He had already anticipated flaws. Now they were simply confirmed. Though regrettable, there was no way he would give up on the one technique capable of changing his fate.
There was no alternative.
Sage Mode? He had tried before, but never even managed to begin, and it was too dangerous to attempt recklessly.
Moreover, in the later stages of the story, Sage Mode's power was limited unless the God Tree released all the world's natural energy—something that would never happen.
The Ten-Tails' jinchūriki?
That was a joke.
With his current fragile body, even housing a single tailed beast would likely kill him. The Ten-Tails would be certain death.
Thus, regardless of its flaws, the Demon Assimilation Technique was his only path.
Taking a deep breath, Kurogane Ren looked at the experimental data. It was time for the final phase of testing.
Without wasting a moment, he prepared everything necessary and began.
As for the test subjects struggling—whether animals or ninja beasts—it was useless. The restraints he had designed were inescapable, even for Jonin-level strength. Only those with exceptionally powerful physiques might break free.
Though he was only a Special Jonin, his understanding of ninjutsu and its power was extensive. This entire laboratory was his carefully constructed masterpiece. There would be no accidents.
Forming hand seals, more complex than those of the original technique due to modifications, he completed them swiftly.
"Ninja Art—Demon Assimilation Technique!"
Kurogane Ren watched coldly as the fusion process unfolded. He had seen this transformation many times already.
Finally, the fusion was complete.
He turned to the instruments on the operating table. It was time to verify the results.
A faint, almost devilish smile appeared on his face.
He felt no psychological burden. None of the subjects who ended up on his table were innocent.
Even so, he knew that if concepts like heaven and hell truly existed, he would undoubtedly be condemned to the deepest levels.
But that was a matter for after death.
As long as he was powerful, who could judge him?
Before long, Kurogane Ren finished recording the results.
Still, he wasn't in a hurry.
A single successful experiment—even one that matched all predictions—was not enough. He needed multiple trials to ensure stability.
After several more experiments, each one proceeded flawlessly, aligning perfectly with his expectations. Not a single unexpected outcome occurred.
Only then did Kurogane Ren finally relax.
Yet he didn't immediately proceed with fusing the Uzumaki bloodline. Instead, he washed up and lay down to rest.
After so many days of intense work and meticulous experimentation, his mind still felt sharp—but he knew it was only the illusion of excitement.
He needed to return himself to peak condition before taking the most critical step of his life.
Meanwhile, elsewhere.
In a dark cavern, the man presumed dead by Konoha—Obito Uchiha—had finally regained full control of his body.
Opposite him stood a figure aged to the brink of death—the once-dominant overlord of the ninja world, Madara Uchiha.
Seeing Obito's condition, Madara knew the time had come to set the next phase of his plan in motion.
Listening to Obito's excited talk about returning to Konoha to reunite with his companions, a faint, almost imperceptible smile formed on Madara's lips.
Yes… this was perfect.
The purer the heart, the more devastating the collapse when hope was shattered. Only then could he awaken the Mangekyō Sharingan and become a worthy pawn.
As for the girl Obito kept mentioning, Madara already knew who she was through Black Zetsu—and just how important she was to him.
The Mist ninja…
It was time for them to act.