"Aizen-sama."
"This is...?"
Just as Aizen Sōsuke was pondering, the young man standing behind him suddenly spoke cautiously.
Yakushi Kabuto also kept his gaze on the blade embryo, his eyes seemingly filled with some confusion. Hidden deeper within that gaze was cautious probing, and a subtle fear of somehow being exposed to such a secret.
Yakushi Kabuto had always been a very pragmatic person.
When he was in Root, he was a competent assassin and spy.
When he followed Orochimaro, he was an excellent mole and research assistant.
Later, when he was dispatched to Sasori's side, he was an outstanding double agent.
No matter when or where, he always moved in a direction that benefited his own survival, and in all dangerous situations, he could find the most suitable position for himself.
Because of this, after Orochimaro-sama died and this man appeared before him, Yakushi Kabuto quickly accepted the fact that he had been 'captured' and swiftly showed enough submission to the man in front of him.
"This is the research I'm conducting, Kabuto-kun."
Aizen Sōsuke seemed completely oblivious to the other party's cautiousness, speaking in a relaxed tone: "A weapon that can materialize a person's spirit."
"However, it's still an unfinished product for now."
The moment he heard this, Yakushi Kabuto's heart immediately tightened, but his expression didn't change at all:
"Truly remarkable research."
"Is its main body also Wood Release cells?"
"To be precise, it should be the god tree factor—that's the name I've given to this property."
Aizen Sōsuke turned to look at him, his palm gently resting on the young man's head, as if completely unaware of the young man's increasingly respectful expression, and smiled gently: "Kabuto-kun, do you know how Chakra is formed within a Ninja's body?"
"It's through the combination of spiritual energy and physical energy," Yakushi Kabuto replied obediently, bowing his head, his voice without the slightest hesitation, perfectly demonstrating his value.
"Then, why did Ninja only appear a thousand years ago?" Aizen Sōsuke continued to ask.
"Because... the accumulation of human civilization's research on the body required a long time as a transition?"
However, just the second question made Yakushi Kabuto, eager to quickly demonstrate his value to this man, begin to hesitate.
"No."
Aizen Sōsuke released his hand and shook his head slightly: "It's because, until a thousand years ago, the [Chakra Pathway System] organ might not have existed in human bodies."
Yakushi Kabuto was stunned.
How could that be?
The concept of Chakra Pathway System, for a Ninja, is a basic theory that they encounter from their very first lesson in becoming a Ninja.
Aizen Sōsuke's voice continued: "Over the years, I have dissected countless bodies of Ninja and civilians. Everyone's body contains an existence called the Chakra Pathway System."
"However, this organ is independent of all physiological systems. It is clearly a complete network more complex than blood vessels and nerves, yet it neither participates in blood circulation nor intervenes in the nervous system, as if it was naturally created to transmit energy."
"Just like an outsider."
"This does not align with existing theories of species evolution."
"Therefore, I became curious."
"Until I consulted countless ancient texts and finally found a common origin from numerous ancient records—the god tree."
Hearing this, Yakushi Kabuto's heart couldn't help but skip a beat, his expression growing more serious.
Aizen Sōsuke's voice continued: "After that, by connecting it with the Wood Release that was once demonstrated by Shodai(1st)-sama in the past, and gaining a deeper understanding, I gradually began to form connections."
As he spoke, he turned to look at the young man beside him and raised a finger, like a gentle teacher, patiently guiding him:
"Kabuto-kun, do you know?"
"In tropical and subtropical regions, there exists a type of holoparasitic plant called Balanophoraceae."
"They survive entirely by attaching to the host's body and absorbing nutrients, inducing the host to extend vascular Roots to connect and interlock with them, intercepting nutrients from the host's body to produce their own fruits."
"At the same time, a small portion of them can actively secrete special signals to prevent the host from being infested by pests, thus possessing certain ecological value."
Listening to the other party's words, Yakushi Kabuto subconsciously widened his eyes and said in astonishment:
"Aizen-sama."
"Are you saying that the Chakra Pathway System is a... plant parasite that lives inside the human body?"
"Originally, I couldn't be sure."
Aizen Sōsuke turned his head back to look at the blade embryo in front of him: "Until I isolated the complete Chakra Pathway System from dozens of corpses and conducted a precise comparison with Orochimaro-sama's Wood Release cell research, I found that there was indeed a high degree of similarity in some genetic structures."
"I named it the 'god tree factor'."
"That well-known legend is probably indeed the origin of all Chakra in the Ninja World... Kabuto-kun should have heard of it."
Yakushi Kabuto had certainly heard of it.
The god tree, born at the world's origin, bore fruit. The goddess Kaguya swallowed it, thereby gaining the power to quell all wars in the world, becoming a deity standing among humans.
However, over a long period, she transformed into an unprecedented evil god.
Eventually, the Six Paths Sage stepped forward and sealed her on the moon.
This was a myth that all Konoha children had heard.
But, wasn't this just a myth?
If all of this had truly existed, then... just imagining the scenes described in that myth sent shivers down Yakushi Kabuto's spine.
Just how terrifying was that power?
So, this man's goal is to recreate the powers that existed in those myths?
The young man's thoughts grew more complex.
But then, he seemed to notice a problem in Aizen Sōsuke's words.
Parasitic plants.
Human host.
Absorbing the host's nutrients.
Bearing fruit.
Yakushi Kabuto subconsciously asked: "If our Chakra Pathway System is truly a parasitic plant, then... what about their fruits?"
Aizen Sōsuke looked at him and retorted:
"Indeed."
"What about their fruits?"
Yakushi Kabuto was startled, inexplicably recalling the earlier myth once again.
—The fruit swallowed by Kaguya.
The young man's body completely stiffened.
Looking at his expression, which vaguely showed some disbelief, Aizen Sōsuke shook his head, his gaze returning to the blade embryo before him:
"In short, what this factor contains is by no means a limited power like Wood Release, but rather more possibilities."
"This is what I will continue to explore next."
"This blade you see now is merely a preliminary result in my process of seeking the truth."
"Next, I will try to integrate the underlying operating logic of the Sharingan and Byakugan into this blade... I hope the results will satisfy me."
This idea was not a sudden whim, but the result of countless searches.
Unlike the various Bloodline Limits currently existing in the Ninja World, which are derived from the fusion of multiple Chakra natures, the truly most ancient and mysterious Bloodlines are actually only three:
The special physique of the Senju Clan.
The Sharingan of the Uchiha Clan.
The Byakugan of the Hyuga Clan.
As for other bloodlines, they are merely derivatives of intertwined Chakra natures.
At the same time, these three also share a common origin.
Which is the god tree.
Or rather, the mysterious Six Paths Sage and Hamura Ōtsutsuki.
Since that's the case, combining them back into one should yield a good product, right?
Aizen Sōsuke thought.
The only problem was that this project required an enormous amount of resources, energy, and wealth. As an ordinary researcher, he, with his current identity, simply couldn't acquire such a large quantity of resources in a short time, let alone the Wood Release cells that Konoha had layers of secrecy shrouding.
—This was one of the reasons he set his sights on Orochimaro.
Also, it was because, throughout the entire Village, Orochimaro was the only man who could make him feel a slight sense of apprehension.
Just like Urahara Kisuke back then.
The problem that still exists now is that a traditional zanpakutō is formed by Ōetsu Nimaiya constructing an Asauchi from a spiritual body, and then a Shinigami infuses their own will into it, thereby giving birth to a materialized representation of their own spirit.
The god tree factor can carry will.
The peak of the Sharingan, the Mangekyo Sharingan, is sufficient to replace spiritual materialization.
The Byakugan possesses a special property of fusing with different bloodlines, inherently having unlimited potential, making it an excellent catalyst.
Therefore, he needs at least one pair of pure [Mangekyo Sharingan] and a relatively large number of [Byakugan] as the foundation for his zanpakutō research.
Aside from that, the fundamental soul of the zanpakutō itself still lacks a suitable replacement.
However, Aizen Sōsuke did have an idea.
As he continued to ponder, Yakushi Kabuto had already recovered from the initial shock and cautiously asked:
"But, Aizen-sama."
"Why... would you tell me all of this?"
"I'm just an ordinary Chunin."
What he didn't say aloud was that just an hour ago, he was still Orochimaro's subordinate, and he had only just been captured and brought here. Why would he receive such trust from the other party? And by what right could he access his deepest secrets?
Yakushi Kabuto didn't understand.
How could he know that Aizen Sōsuke's attention on him wasn't just for a day or two?
However, listening to his words, Aizen Sōsuke seemed rather indifferent. He slowly walked to the desk in the center of the laboratory, sat down, and then cast a gentle gaze upon him:
"The word 'trust' is synonymous with 'reliance'."
"Those are actions of the weak."
"We don't need them."
"If it were me, I would only ask if you want to come with me, not to trust me and come with me."
"Don't trust anyone, and that includes me."
He said this, interlacing his fingers on the table, quietly looking at the young man across the desk, his gaze behind the thick glasses showing a hint of encouragement, his tone gentle:
"So, are you willing to follow me and explore the truth of this world?"
"Kabuto-kun."
These were the plainest of words, yet they caused Yakushi Kabuto, who had experienced countless betrayals, killings, commands, and loyalty tests since childhood, to involuntarily freeze.
As if his deepest spirit had been directly touched.
Suddenly, Yakushi Kabuto's mind recalled that figure deeply etched in his memory—his mother, who never recognized him until her death.
Yakushi Nonou.
'Don't trust anyone, and follow him?'
'...I couldn't ask for more.'
Suddenly, he seemed to let go of something, and his whole being became lighter.
No need for loyalty, no need for trust.
Just following behind him, exploring the true face of this world.
Thinking of this.
When he looked up again, meeting Aizen Sōsuke's gaze, a false yet brilliant smile appeared on the young man's face.
As if the mask had finally melted onto his face, merging with his true appearance.
Then, he decisively knelt on one knee.
Yakushi Kabuto sincerely bowed his head and said:
"Yes."
"Aizen-sama."