After returning home, Kagami immediately shut all the doors and windows. Then, unable to contain his anticipation, he spread out the secret technique scroll containing the Yin Seal in his bedroom.
With just a cursory glance, he spotted traces of the Uzumaki clan’s fuinjutsu among the many sealing formulas that made up the Yin Seal.
Clearly, the person who had originally developed the Yin Seal must have been a member of the Uzumaki clan—and one with extremely profound mastery of fuinjutsu and an exceptionally meticulous mind. There was even a good chance that the developer had been a woman.
Afterward, Kagami lightly ran his fingers across the fuinjutsu scroll as he began studying it word by word, line by line.
Throughout the process, his brows would occasionally knit together as he sank into deep thought, only for the corners of his mouth to rise into a smug smile moments later.
Before he knew it, two or three hours had passed.
"Phew..."
Letting out a soft breath, Kagami finally looked away from the scroll.
The Yin Seal was exactly as he had anticipated. It was indeed an extremely advanced and exquisitely designed secret technique.
With Kagami’s mastery of fuinjutsu, he could easily tell that the Yin Seal had undergone refinement across several generations. Every conceivable aspect had been taken into consideration by successive developers, turning it into an exceptionally mature secret technique with virtually no hidden dangers or flaws.
But precisely because the Yin Seal had been perfected to the point where it possessed almost no hidden dangers or flaws, the difficulty of mastering it had increased severalfold as well.
It placed almost excessively stringent demands on both the practitioner’s mastery of fuinjutsu and their ability to control chakra.
As far as Kagami could remember, there were only three people he knew of who had successfully mastered the Yin Seal: the first Nine-Tails jinchuriki, Uzumaki Mito; Tsunade; and, in the original timeline, Tsunade’s disciple, Haruno Sakura.
Of these three, the first two were powerhouses of the Uzumaki and Senju clans respectively. Whether in terms of bloodline or aptitude as shinobi, they belonged among the very best in the entire shinobi world.
As for the third, Haruno Sakura, although she possessed no particularly powerful bloodline, her talent for chakra control ranked among the very best of the Konoha Twelve.
Meanwhile, Shizune, despite being Tsunade’s direct disciple, had failed to master the Yin Seal due to the limitations of her own aptitude. From this alone, it was obvious just how demanding the Yin Seal was of its practitioners!
But none of that was what gave Kagami the biggest headache.
What truly troubled him was that, just as Tsunade had said, the Yin Seal really was a secret technique that only women could cultivate.
Perhaps the original Yin Seal could have been cultivated by both men and women. However, because the developers who had refined the Yin Seal throughout the generations were likely all women, the technique had gradually become increasingly tailored to the female body.
As a result, men encountered far more obstacles when attempting to cultivate the Yin Seal. And considering how demanding the technique already was to begin with, under normal circumstances, it was practically impossible for a man to successfully master it.
Still, Kagami had a fair amount of confidence in both his mastery of fuinjutsu and his chakra control. Thus, he quickly cast aside his apprehension and began attempting to cultivate the Yin Seal.
Like all fuinjutsu, the core of the Yin Seal lay in its sealing formula.
The difference was that its sealing formula was not engraved onto an enemy’s body, but onto the practitioner’s own body—and specifically, onto the center of the forehead, one of the most sensitive and vulnerable areas of the human body.
This placed extremely high demands on the practitioner’s understanding of human anatomy.
Fortunately, Kagami was a member of the Hyuga clan and possessed the Byakugan. He had received rigorous education in this field since childhood, and on top of that, his many years of research into human cloning had given him an extraordinarily deep understanding of the human body.
He might not dare claim to be number one in the current shinobi world when it came to human anatomy, but he could at least rank among the top ten.
So this particular hurdle posed no difficulty for him. He could attempt it again and again without worrying about accidentally damaging his own brain tissue.
He gathered his chakra...
Forming hand seals...
Engraving the sealing formula...
Kagami followed the steps recorded in the secret technique scroll, executing every stage in one smooth motion. His execution was virtually flawless!
After successfully engraving the Yin Seal’s sealing formula onto the center of his forehead, Kagami slowly opened his eyes and examined himself in the mirror before him.
Sure enough, the Yin Seal’s distinctive diamond-shaped mark had appeared on his forehead.
"Did it work?"
Kagami was immediately delighted, but his brows quickly furrowed again.
He had suddenly realized that the Yin Seal’s sealing formula engraved on his forehead had not connected to all the chakra pathways throughout his body as described in the secret technique scroll.
And if the sealing formula on his forehead could not connect to the chakra pathways throughout his body, then naturally, it would be unable to absorb and store chakra.
"How could this happen? Which step went wrong?"
Kagami suppressed his impatience and calmly began reviewing the entire process step by step.
Yet after thoroughly checking everything, he found no mistakes or omissions in his execution.
So he dispelled the sealing formula he had just engraved and tried again.
But the result remained the same.
No matter how many times he tried, the sealing formula he engraved simply refused to connect with the chakra pathways throughout his body.
"Could it be because of the differences between the male and female body?"
In that moment, Kagami arrived at a conclusion.
There was no way Tsunade would have given Rei a fake secret technique scroll for the Yin Seal, and there had been no mistakes in his own execution.
That left only one explanation—the structural differences between male and female bodies.
Perhaps the exact same procedure would succeed when performed by a woman, but simply could not succeed when performed by a man.
"It must be caused by the subtle differences between the chakra pathways of men and women!"
Kagami was somewhat irritated. If his guess was correct, then the problem wasn’t with him—it was with the Yin Seal itself.
But Tsunade had only given him seven days.
That amount of time was more than enough to learn the Yin Seal, but to modify the Yin Seal and make it suitable for men to cultivate?
Seven days was nowhere near enough.
"No wonder Tsunade wasn’t in any hurry to take the secret technique scroll back. Looks like she’s absolutely convinced I won’t be able to master the Yin Seal."
Kagami finally understood.
Tsunade was certain that he wouldn’t be able to learn the Yin Seal, which was why she had been willing to use the secret technique scroll as part of their deal.
On the surface, it appeared to be a fair exchange.
But in reality, Kagami would simply be doing Tsunade a favor for nothing in return.
Not only could Tsunade smoothly put the matter of Kagami stealing the secret technique behind them, she could also have him help suppress the Uchiha clan.
After all, the current Kagami was no longer some insignificant figure who could be pushed around at will. Even if Tsunade genuinely wanted to punish him, she would have to consider the consequences from every angle—Kagami’s potentially fierce resistance, as well as the attitude of the Hyuga clan.
"Tch, you dare underestimate me!"
Kagami clicked his tongue.
Then, without hesitation, he reached into the ninja pouch at his waist and pulled out the storage scroll containing his Fire Release clone...