"...Aizen-sama."
"What… is that?"
As Aizen stood silently in thought, the young man behind him finally spoke up, his voice cautious, almost hesitant.
Kabuto's gaze remained fixed on the sword embryo before them.
There was curiosity in his eyes, but beneath that curiosity hid a trace of fear—a quiet, instinctive dread of having come too close to something that should have remained unknown.
Kabuto had always been a man who understood the times and adapted to them.
When he served under Root, he was an efficient assassin and a reliable spy.
Under Orochimaru, he became a competent agent and laboratory assistant.
Later, when he was sent to Sasori, he had played the role of an excellent double agent.
No matter where he was, Kabuto always knew how to survive. He could find his place even in the most dangerous of situations.
That was why, after Orochimaru's death and this man's sudden appearance, Kabuto had quickly accepted his new role as a captive—and just as quickly, he had shown this man the obedience he wanted to see.
"This," Aizen said softly, "is my current research, Kabuto-kun."
"A weapon that can give form to the human soul."
"Though for now, it is still incomplete."
At those words, Kabuto's heart clenched, though his expression remained perfectly calm.
"An incredible field of study," he said evenly. "Is its base also derived from Wood Release cells?"
"More precisely," Aizen replied, "from something I've chosen to call the Divine Tree Factor."
He turned toward Kabuto, resting his palm lightly on the boy's head. His smile was gentle, unassuming, as though he hadn't noticed the growing reverence and caution in Kabuto's eyes.
"Kabuto-kun, do you know how a shinobi's chakra is formed?"
"It's the combination of spiritual and physical energy," Kabuto answered without hesitation, head bowed in obedience—his tone flawless, the answer perfect.
"Then tell me," Aizen continued, "why did shinobi only appear a thousand years ago?"
Kabuto paused. "Because… human civilization needed time to accumulate knowledge of the body?"
Aizen shook his head slightly. "No. It's because, before that time, the human body likely did not yet possess what we now call the chakra network."
Kabuto froze. That was impossible.
The chakra network was among the first lessons any shinobi learned—it was as fundamental as life itself.
Aizen continued calmly, "Over the years, I've dissected countless bodies, shinobi and civilian alike. Every single one has a network of pathways—what we call the chakra system."
"Yet this system is unlike any other organ. It is more complex than the blood vessels or the nerves, but it connects to neither. It serves only one purpose—to conduct energy."
"As though it were something alien."
"It does not fit with the known laws of evolution."
"So I began to wonder."
"After reading through countless old scrolls, I finally found a single recurring name at the origin of every legend—the Divine Tree."
Kabuto's heart skipped a beat, his face growing more solemn.
Aizen went on, "When I compared the chakra network with the Wood Release cells once extracted from the First Hokage, the similarities in their structures became undeniable."
He raised a finger, like a patient teacher guiding a student.
"Kabuto-kun, did you know that in tropical and subtropical regions, there exists a parasitic plant family known as the Balanophoraceae?"
"They survive entirely by attaching themselves to a host, absorbing its nutrients, and forming root structures that fuse with those of the host.
In return, a few of them secrete special substances to protect their hosts from pests, creating a form of ecological balance."
Kabuto's eyes widened unconsciously. "Aizen-sama… are you saying the chakra network is a kind of parasitic organism—one that lives within the human body?"
"I wasn't certain at first," Aizen replied, turning his gaze back toward the white sword embryo.
"But after isolating dozens of complete chakra networks and comparing them with Orochimaru's Wood Release samples, I found that part of their genetic structure matched almost perfectly."
"I named it the Divine Tree Factor."
"The ancient legend, it seems, may not be a myth at all. It may truly be the origin of all chakra in this world."
Kabuto had, of course, heard that legend.
The Divine Tree that grew at the dawn of the world had borne a sacred fruit. The goddess Kaguya had eaten it and gained the power to end all wars, becoming a divine being upon the earth.
But over time, she had transformed into a monstrous god of destruction.
In the end, the Sage of Six Paths rose to oppose her and sealed her away upon the moon.
It was a story every child in Konoha had heard before.
But… what if it wasn't a story?
If all of that had truly happened… what kind of terrifying power had once existed in this world?
And this man—was he trying to recreate that power?
As these thoughts churned through Kabuto's mind, he caught on one particular detail in Aizen's explanation.
A parasitic plant. A human host.
Absorbing the host's nutrients.
Producing a fruit.
Kabuto asked quietly, "If the chakra network really is a parasitic organism… then what about its fruit?"
Aizen turned toward him, his tone as mild as ever.
"Indeed," he said. "What about its fruit?"
Kabuto froze. His mind went back, unbidden, to the myth—the fruit that Kaguya had eaten.
His entire body stiffened.
Seeing Kabuto's stunned expression, Aizen simply smiled faintly and looked back at the sword embryo.
"In any case," he said, "the Divine Tree Factor is far more than what Wood Release could ever hope to be. It holds limitless potential."
"That is what I intend to explore next."
"What you see before you is merely a preliminary result of that exploration."
"Next, I plan to integrate the fundamental structures of the Sharingan and the Byakugan into this sword. Hopefully, the outcome will be… satisfactory."
It wasn't an impulsive idea. It was the culmination of years of meticulous thought.
Among all the bloodlines in the shinobi world, there were only three that could be called truly ancient and mysterious.
The special physique of the Senju clan. The Sharingan of the Uchiha clan. The Byakugan of the Hyuga clan.
All other kekkei genkai were merely derivatives—variations born from the blending of chakra attributes.
These three, however, shared a single origin.
The Divine Tree.
Or, more precisely, the two brothers known as the Sage of Six Paths and Hamura.
If that was the case, then recombining their legacies might yield something remarkable indeed.
Aizen's eyes narrowed slightly.
The problem, however, was that the project required immense resources—funds, energy, and materials far beyond what any ordinary researcher could acquire.
The Wood Release cells, buried deep beneath Konoha's classified archives, were practically untouchable.
That was why he had turned his attention toward Orochimaru in the first place. And also why Orochimaru was one of the few men he truly regarded with caution.
Just like Urahara Kisuke, once upon a time.
The remaining issue was the essence of the Zanpakutō itself.
Traditionally, a Zanpakutō was born when Ōetsu Nimaiya forged an Asauchi from spiritual matter, and a Shinigami infused it with their own will—giving physical form to the shape of their soul.
The Divine Tree Factor could serve as the vessel for that will.
The Mangekyō Sharingan could stand in for the soul's manifestation. And the Byakugan, capable of merging with various bloodlines, made a perfect catalyst.
To begin, he would need at least one pure pair of Mangekyō Sharingan and a substantial number of Byakugan to form the foundation of his research.
But there was still one problem—the core soul that would serve as the Zanpakutō's base.
Aizen was still searching for a replacement.
As he pondered this, Kabuto finally regained his composure and ventured carefully,
"But, Aizen-sama… why tell me all this?"
"I'm only an ordinary chūnin. Why would you share such secrets with me?"
He didn't say the rest: that barely an hour ago, he had still been Orochimaru's subordinate—recently captured, uncertain of his fate.
Why would this man trust him so easily?
He couldn't understand.
But Aizen's expression remained calm, almost indifferent. He walked to the desk at the center of the lab and sat down, looking at Kabuto with quiet warmth.
"Trust," Aizen said softly, "is the same as dependence."
"It is the behavior of the weak."
"We have no need for it."
"If it were me, I would not ask you to trust me and follow. I would simply ask—do you wish to walk beside me?"
"Never trust anyone. Not even me."
He folded his hands upon the desk, his gaze steady behind the gleam of his glasses. There was encouragement in his tone, the faintest trace of something like kindness.
"So, Kabuto-kun," he asked, "will you walk with me—to uncover the truth of this world?"
The words were spoken simply, yet they pierced straight through Kabuto's heart.
For someone who had lived his entire life under orders, betrayals, and shifting loyalties, they struck a chord deep within.
He thought suddenly of the one person who had ever cared for him—his foster mother, Yakushi Nono—who had died without even recognizing him.
"Do not trust anyone," Aizen had said. "Just follow."
It was almost… liberating.
No faith, no loyalty—only purpose.
To follow, and to uncover the truth.
As the thought took root, Kabuto felt something in him quietly unwind.
When he raised his head again to meet Aizen's eyes, his face bore a bright, perfect smile—one that concealed the emptiness beneath.
Like a mask melting seamlessly into the flesh. Then, without hesitation, he dropped to one knee.
"Understood," he said.
"Aizen-sama."