Beneath the Hokage Rock, a hundred meters below.
Hiruzen used Earth Release to slip down to this place, breaking through layer after layer of seals before arriving at a long, narrow underground chamber.
A faint stench of decay lingered in the air. The four walls and the vaulted ceiling were formed of ink-dark rock hardened by Earth Release.
Rust-flecked experiment tables stood in rows alongside cultivation tanks lining the walls, each containing all manner of "materials."
At the far end, one cultivation tank was particularly eye-catching. Dense sealing techniques covered its surface, and a thick, transparent flexible tube extended from its base, inserting into another storage vessel.
This was Senju Tobirama's secret vault.
Long ago, he himself had not been absent from this place.
But Senju Tobirama's research ideas were, in truth, somewhat shocking to the world…
After only a cursory review, having judged that he could neither control them nor meaningfully continue them, he had reinforced the seals, taken the notebooks, and sealed most of the equipment deep beneath the earth.
Hiruzen had long taken a keen interest in this.
It was just that when he had first arrived in the shinobi world, this matter could not be placed at the forefront.
Now that he could free his hands a little, the Hokage came here with barely concealed enthusiasm.
Recalling how, twenty years earlier, his unfamiliarity with Tobirama's defensive arrays during his first visit had nearly gotten him blown up, he could not help but smile faintly.
Holding the Second Hokage's research notes, Hiruzen went through these astonishing half-finished works one by one, confirming each of them.
"Tsk… this pitch-black puddle—this is probably that monster meant to absorb the negative energy in people's hearts, isn't it? What a pity—it has no vitality left…"
Hiruzen marveled at Tobirama's creativity.
The Second Hokage had once proposed a concept: to use the negative energy that would forever arise in the human heart to create a monster that lived off it, as an artificial tailed beast.
The Second Hokage called this the "Zero-Tails."
"And there are even several Sharingan… single tomoe, and a pair of three-tomoe…" These were most likely spoils seized during the Warring States Period.
It was just that the quantity was a bit less than Hiruzen had imagined.
After all, in Tobirama's notes, the research on the Sharingan could be said to be meticulously organized.
From its causes and structure to its specific mechanism of action—he even listed out a methodology for awakening it.
If he were to fetch a three-tomoe one from the Uchiha clan compound now, and have it debate the Sharingan with Senju Tobirama…
Hiruzen believed his sensei could talk the other party into complete conviction.
At this level, in his previous life he must have been a Mangekyō Sharingan—otherwise how could he understand it this well?
All one could say was—
No one understands the Uchiha better than Senju Tobirama!
Walking up to the cultivation tank like a black coffin, Hiruzen raised his head and stared.
He could vaguely guess some of it.
Based on the research notes and Hiruzen's own memories, plus a small bit of inference.
Before the First Shinobi World War occurred, Senju Tobirama was already thinking about how to use bioengineering technology to strengthen Konohagakure…
The first thing he thought of was the problem of injured shinobi.
Ninjas rely on hand seals; helping ninjas with damaged limbs recover their bodies was, in both intent and application, clearly a righteous path—a light of orthodoxy that fit well with the Will of Fire…
But as things gradually developed, Tobirama began turning his thoughts to the problem of cloning an entire person.
This, Hiruzen could also understand…
After all, setting aside figures like Senju Hashirama and Senju Tobirama at that level—
Even the body of an elite jōnin, even if used as something like a puppet, would still possess considerable combat power.
But clearly, Senju Tobirama failed.
According to his research results, for a chakra-bearing ninja, developing from cells into a full human body was far more than a matter of the genome alone.
The more talented the ninja the cells came from, the more likely cloning attempts were to grow into a mass of chaotic, useless tissue.
Tobirama conjectured that this phenomenon might be closely related to factors such as the subject's developmental environment and the nourishment and circulation of chakra during growth, and he listed numerous interfering variables as well…
With Hiruzen's current level of understanding, both he and Tobirama believed that ninja cloning would be difficult to replicate on a large scale unless the subject's body possessed some special characteristic.
One could only proceed by making step-by-step micro-adjustments, carrying out continual experiments, and relying on sheer trial count to happen upon the correct result.
This problem might only find some solutions once technology developed further.
After undoing the external seals of the black coffin, what entered his sight—
Was a youth's body that felt both familiar and unfamiliar, roughly fourteen or fifteen years old.
He had a head of messy black hair, handsome features, and brows and eyes that somewhat resembled Senju Tobirama, yet were not entirely the same.
"Hehe, sensei…"
Alone in the laboratory, the Hokage—normally quite steady in temperament—felt the corner of his mouth twitch unconsciously.
"Although I've never seen it myself, the target of this cellular fusion is probably that person you keep mentioning in your notes, isn't it?"
That person was named Uchiha Izuna!
Hiruzen tilted his head and looked toward the other area connected to the tank.
Inside were large quantities of cells that looked almost woody; with the slightest sense, he could tell they belonged to Hashirama.
"Letting the water infused with Hashirama cells, filtered through sealing techniques, circulate to nourish this body?"
Whether ordinary people have a habit of keeping diaries is hard to say.
But researchers certainly have the habit of keeping records.
Cut down while holding the rear on the battlefield, Tobirama had not had time to erase his "life browsing history," allowing Hiruzen—the inheritor of his legacy—to see everything clearly.
And with great relish, at that!
After seeing this experimental subject, Hiruzen's imagination ran wild. He suddenly connected some scattered phrases from the notes, constructing a small story.
One day, Tobirama pierced an enemy's chest with the Flying Thunder God Slash, tearing away a piece of flesh.
He preserved it and began experimental development.
Later, after becoming Hokage and gaining access to resources, during one experiment—and driven by some strange impulse—he attempted to develop his enemy's cells.
He then discovered that once he added his own cells, experiments that had always ended in complete failure finally showed a turning point.
After who knows how many micro-adjustments and revisions, he actually managed to produce a fully formed human body!
He then solidified it within the cultivation tank using multiple sealing techniques.
Waiting to return from the battlefield, he would continue the research…
Only—
Hiruzen stared at the joints of this body and discovered what seemed to be defects, like the nodular abnormalities that appear when chakra pathways are severed.
Having long since read—and nearly memorized—the notes, he immediately thought of the critical bottleneck involved.
—"What could help auxiliary chakra transmission flow smoothly?"
—"Sister-in-law Mito might know, but if I ask her, she'll notice my intentions."
—"Troublesome… Big Brother repeatedly told her to keep an eye on my research."
Of course, none of this was actually written in the notes. There were only rough scribbles—phrases like "chakra transmission" and Mito's name crossed out.
Yet Hiruzen's eyes seemed to pass through time itself, glimpsing Tobirama's thoughts from back then…
Whether it was true or not, he decided to reason it out this way first!
After all, the dead could not refute him—for the time being…
Hiruzen felt a twinge in his teeth.
What Tobirama had done to Uchiha Izuna—"to the death" scarcely sufficed to describe it.
Swap the genders, and it would be enough to dominate the rankings of a tragic love-and-hate novel.
He truly could not understand the matters between the Senju and the Uchiha…
"I was still worrying about the body itself. Now that there's a ready-made one, it's convenient—just needs a bit of refinement."
"Since you didn't dare ask Mito-sama, sensei, I'll ask for you!"
The Hokage of Konohagakure slowly closed the seals on the tank.
Without him, this research might have remained buried beneath Konohagakure forever.
As time passed, it might have collapsed—or been completely erased by some later Hokage as a forbidden historical zone.
But now, things were different.
Konohagakure had to begin accelerating!
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