Orochimaru burst into manic laughter.
"Ha—ha—ha! This is it! This is the truth!"
Nagi withdrew his Yin chakra, allowing Orochimaru to examine the Mangekyō Sharingan more clearly.
Though greed burned in his eyes, a voice deep within Orochimaru told him—
This is not the end. This is not the end.
After observing it for a long time, he finally tore his gaze away.
At this moment, his admiration for Nagi reached an unprecedented height. The secret of the Mangekyō Sharingan… had truly been unraveled.
Nagi, however, felt it was partly luck.
On one hand, he seemed able—though he did not fully understand why—to control high-quality Yin–Yang chakra.
On the other hand, he and Tobirama Senju had thoroughly analyzed Fugaku Uchiha's Mangekyō Sharingan.
Perhaps in the future, the Uchiha clan would no longer need to rely on cruel methods to evolve their Sharingan.
Fugaku might even end up thanking them.
Nagi continued, deliberately broadening Orochimaru's perspective.
"In truth, this eye possesses only the dōjutsu of the Mangekyō Sharingan—but no unique dōjutsu."
"…What?"
Orochimaru froze.
"I have not truly solved the Mangekyō's deepest secret.
Its evolution depends on intense emotional upheaval experienced by the owner of both eyes.
That emotional stimulus generates a special chakra within the brain, which acts upon the optic nerves and transforms the eyes.
This is what is meant by 'the eye that reflects the heart.'"
He continued calmly:
"But that special chakra is, in essence, high-quality Yin Release chakra—combined with emotion-derived chakra.
The latter alters the nature of the former, producing the Mangekyō's unique dōjutsu abilities."
Orochimaru followed the logic.
"I see. So what's missing is the catalyst that transforms the Yin chakra's nature.
That explains it.
The Mangekyō in your hand has dōjutsu—but no awakened technique?"
"Correct."
Nagi went on:
"My experiments show that using the Mangekyō Sharingan consumes vast amounts of Yin Release chakra—or extremely high-quality Yin chakra.
Ordinary Uchiha do not possess sufficient quantity or purity.
So their bodies instinctively draw upon Yang Release chakra to compensate.
But as I said before—Yang chakra is closely tied to physical vitality.
If too much Yang chakra is depleted…"
He paused.
"The body deteriorates.
Most critically—if Yang chakra around the eyes continues to diminish—
The result is blindness."
[Kakashi Hatake: What?! Overuse leads to blindness?!]
He had only ever used his three-tomoe Sharingan—unaware it was already a Mangekyō.
[Ōnoki: That is crucial intelligence.]
[Fourth Raikage (A): So against a Mangekyō user, you just have to drag the fight out?]
[Ōnoki: But wait—Madara didn't seem blind back then!]
[Izuna Uchiha: No. In life, my brother and I both suffered from that problem.]
Within the Akatsuki, several members glanced toward Itachi Uchiha.
Was Nagi correct?
Itachi's expression remained unreadable.
Weakness was not something to reveal.
Beside him, the masked man—Obito Uchiha—lowered his gaze slightly.
So that's why Hashirama's cells grant me protection… High-quality Yang chakra offsets the Mangekyō's side effects.
He regarded Nagi with renewed caution.
Brilliant minds were admirable.
But excessively brilliant ones were dangerous.
Seeing Orochimaru's excitement waver into disappointment—treating the Mangekyō as somewhat incomplete—
Nagi added a final, irresistible lure.
"The Mangekyō Sharingan can evolve further."
"…What?!"
Orochimaru's face contorted in shock.
"Madara Uchiha could not have fought the First Hokage for so long with only the Mangekyō. Otherwise, he would have gone blind many times over."
"…That makes sense."
"According to the Second Hokage's records, Madara transplanted his younger brother's Mangekyō Sharingan after Izuna's death."
"Is that true?!"
Orochimaru felt his worldview shatter yet again.
"Yes.
The First Hokage possessed ultimate Yang Release.
Madara possessed ultimate Yin Release.
Though their chakra quality was comparable, the difference lay in quantity.
Izuna's high-quality Yin chakra compensated for that deficit.
Thus, Madara's Mangekyō evolved once more."
Nagi added calmly:
"Though in truth—Madara might have evolved it without transplantation."
"…Why?"
[Fugaku Uchiha: What?! There's another path to evolution?!]
[Izuna Uchiha: Hmph. Even without my eyes, my brother would have evolved them.]
[Madara Uchiha: …Of course.]
(Even if he wasn't entirely sure.)
Nagi answered:
"As one ages, Madara's Yin chakra would naturally increase.
Quantitative change produces qualitative transformation.
It would only be a matter of time."
Orochimaru nodded slowly.
"For anyone else, I might doubt it.
But he was Madara Uchiha."
"Precisely."
Then Nagi delivered the final strike.
"Perhaps Madara's eyes could evolve even further."
"…Ah? Aah?!"
Orochimaru nearly choked.
Further evolution?
"Who said biological evolution has a limit?
Natural selection. Survival of the fittest.
That is the law of the shinobi world."
With that, Nagi placed several books on the table:
On Biological Evolution
Cellular Studies of the Shinobi World
Genetic Factors in Chakra Transmission
"Your biotechnology will find answers within."
Orochimaru eagerly flipped through them.
"This…!
So that is how cellular structures generate chakra…
Genetic factors operate this way…"
He turned page after page, breath growing uneven.
"…Astounding."
(The shinobi world already possessed microscopes and a rudimentary understanding of cells—Boruto-era science even included paternity testing. Their micro-level knowledge existed—but was fragmented and skewed.)
After scanning through the material, Orochimaru looked up at Nagi.
Then he laughed.
"Hahaha… I understand now. So this is what you meant when you said you needed me.
Even if the issue of Living Corpse Reincarnation remains unresolved—
I cannot step off your ship now, Nagi.
As expected of Root's new leader."
Nagi rose and extended his hand.
"Welcome aboard the great vessel known as Science, Lord Orochimaru."
Orochimaru clasped it firmly.
"No. It is I who should say that.
From this day forward—please take care of me."
Their hands met.
The fish had taken the bait.
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