Kurogane Ren slept for an entire day and two nights.
When he finally opened his eyes again, the first thing he felt was hunger—and at the same time, his mind had finally recovered its clarity.
He stood up and looked at himself in the mirror. For a moment, he didn't even recognize the disheveled figure staring back.
Though he wasn't a clean freak, this state was still unacceptable. After spending quite some time tidying himself up, he looked again at his reflection. His face was still pale, but now he wore a faint smile.
That pallor was likely permanent.
For the sake of his research and training, he had consumed countless soldier pills and pushed his chakra to its limits.
As everyone knew, chakra was a combination of physical and mental energy. His physical energy had been overdrawn for far too long, and his recovery could no longer keep up. That was why his complexion remained so pale.
If this continued, he would undoubtedly become short-lived.
But from the moment he obtained the Demon Assimilation Technique, his path had already changed.
Pushing open the door, Kurogane Ren stepped forward firmly toward a brand-new future.
After filling his stomach, he began making his next arrangements.
First, since he didn't know when Rin Nohara would be captured by the Mist ninja, he needed to begin surveillance immediately. That part was simple—his crows could handle it.
As for the rest, it would take a bit more time.
The next day, Kurogane Ren went to the Hokage's mission board and accepted a relatively complex solo mission. With the mission scroll in hand, he left the village barrier.
Looking at the task written on the scroll, he had no intention of actually completing it.
Because he himself was the one who had issued the mission. It was merely a legitimate excuse to leave Konoha.
After confirming that no one was following him, Kurogane Ren bit his finger, formed hand seals, and pressed his palm to the ground.
"Summoning Technique!"
However, this summoning didn't produce a ninja beast.
Naturally, this was intentional. By using far less chakra than required, the summoning was bound to fail—but at the same time, the intended target would still sense it.
Just like how Madara Uchiha forcibly attempted to summon the Nine-Tails from within Naruto Uzumaki—even if unsuccessful, it would still trigger a reaction.
At that moment, in a dimly lit experimental base, a crow blinked. It was one of Kurogane Ren's summons.
Flapping its wings, it flew over and, following his prior instructions, opened a massive scroll.
Inscribed upon it was another Summoning Technique formula.
In the next instant, outside Konoha, Kurogane Ren's figure vanished in a puff of white smoke—and reappeared inside his experimental base.
Standing within the base, he looked at the various corpses preserved in cultivation tanks before shifting his gaze to the final row.
All of them shared one common trait—their hair was red.
These were corpses of the Uzumaki clan.
He hadn't killed them himself. He had simply instructed his crows to monitor the Land of Whirlpools.
Then, during the destruction of the Uzumaki clan, he took advantage of the chaos to collect some of the fallen bodies.
As for those responsible for their extermination… it could only be said that none of the great ninja villages were clean.
Why choose the Uzumaki clan?
Because to overcome his greatest flaw—his lack of chakra—the most obvious choice was the clan renowned for vitality and longevity: the Uzumaki.
Anyone who had seen the original story would remember the overwhelming chakra reserves of Naruto Uzumaki, even earning him the nickname "Chakra Monster."
Of course, Kurogane Ren understood that ordinary Uzumaki clan members didn't possess chakra on that level. Naruto's power came not only from his Uzumaki heritage, but also from the Nine-Tails and his status as Asura's reincarnation.
But even so, the Uzumaki clan's chakra was far from ordinary.
Kurogane Ren had even devised a simple formula for chakra capacity:
y = x \cdot i
Here, y represented total chakra, x represented physical strength developed through training, and i represented the innate chakra coefficient.
Physical strength could be improved through effort, but the chakra coefficient was something one was born with—it barely changed through training.
Naturally, there were exceptional individuals. People like Jiraiya and Minato Namikaze had high coefficients, representing the peak of ordinary humans.
As for the Uzumaki clan—even the weakest among them had a high coefficient.
This meant that with even moderate training, their chakra reserves would far surpass those who trained desperately but had low coefficients.
After all, not everyone was Might Guy. His immense chakra came from extreme physical conditioning—but even that required exceptional bodily talent.
Finally, Kurogane Ren stopped before one particular corpse.
He couldn't measure its chakra coefficient, but it certainly wouldn't be low.
What he had determined was its chakra nature: wind and lightning.
Exactly two of the three attributes he lacked—and both relatively rare.
It wasn't that he hadn't wanted a body with wind, lightning, and fire. It was simply impossible to find.
There were bodies with three attributes, but not the combination he needed.
Wind was already rare, lightning slightly less so. Finding both together was difficult enough—let alone adding a third element.
Even though fire wasn't rare, the combination remained elusive.
Thus, the corpse before him was his best possible fusion material.
A burning intensity filled Kurogane Ren's eyes. Once he fused with this body, his chakra problem would likely be resolved.
But…
Now was not the time.
Though he had thoroughly studied the Demon Assimilation Technique, he had never performed it himself. He couldn't guarantee success on the first attempt.
And since it involved his own body, he had to be extremely cautious.
He needed to suppress his excitement and begin with experiments—starting with animal corpses. Fortunately, he had plenty of expendable materials for testing.
Only when he was absolutely certain would he proceed with the final step.
"Hopefully, there's enough time."
Using the Clairvoyance Technique, Kurogane Ren glanced at Rin Nohara, who was still mourning Obito Uchiha's "death" while visiting Kakashi Hatake.
He narrowed his eyes.
He didn't care about her fate.
What mattered was that the Mist ninja would implant the Three-Tails into her.
A complete Tailed Beast was far too conspicuous—something that would likely attract the attention of figures like Madara Uchiha or Black Zetsu.
But just a portion of a Tailed Beast's chakra…
That, he wanted.