Hyuga Natsu's issue did not originate from within, but from without.
Similar to the situation faced by previous generations of Tennin, the root cause lay in awakening her Yin Release Tenseigan chakra after breaking through the shackles of the Caged Bird seal—which subsequently resonated with the Giant Tenseigan located on the moon.
The only reason she could still maintain her self-awareness was that her Yin Release Tenseigan chakra acted as an intermediary buffer.
However, this process had already begun.
Even if medical ninjutsu were used to sever and reconstruct her chakra pathways, or if that collective will were stripped and decomposed from Natsu's chakra, the outcome could not be stopped.
At this point, the only method Hyuga Yu could think of to save Natsu's life was—
A true Tenseigan!
Only by completing the cultivation of the Hamura lineage's Sage Body alongside a complete Tenseigan within less than three months—thereby reaching Six Paths-level power—would there be a chance to preserve Natsu's life!
On the afternoon of March 5th, without leaving any time for tenderness, Natsu—having been informed of the full scope of the requirements and seeming to have long been prepared for this—directly mobilized an initial batch of twenty-three people from within the Hyūga clan to report to the Headquarters.
This group consisted of high-ranking Branch House members originally tasked with managing assets for the seven main branches of the Main House. They included both clan shinobi and civilians who had handled assets measured in tens of millions and hundreds of millions of ryo. Their competence and loyalty had been verified by the Main House itself.
This aligned perfectly with Yu's requirements.
After all, he wasn't the one who had wiped out the Main House. Now that the Main House was essentially eradicated, these people actually had to thank him for standing above them as a "Tennin unrestrained by the Caged Bird"—preventing an internal mutiny and keeping their family assets from being plundered.
At the same time, Yu received an audited inventory of the Hyūga clan's assets from Natsu—
Fixed assets belonging to the Hyūga clan alone within the Land of Fire—including real estate, storefronts, farmland, and smelters—exceeded 10 billion ryo.
It was truly wealth capable of rivaling a nation.
Excluding the massive dividends used to maintain the Branch House's loyalty and operational needs, the liquid capital on the books still amounted to nearly 600 million ryo.
And that was merely what was recorded on paper...
To fully mobilize this behemoth known as the Hyūga clan, Yu wasn't stingy. He mobilized all the Main House assets that now belonged to him in theory, issuing stock option dividends based on the corporate operational model of his past life. He also disbanded the original structure of the seven main branches and established the prototype of an internal audit department.
Rewards were guaranteed for merit, and punishment for misdeeds.
With Yu playing the bad cop and Natsu playing the good cop, the Hyūga clan—which had begun showing early signs of chaos—quickly settled down. Following Yu's vision, a vast number of Hyūga clan personnel were deployed into Yu's grand plans.
They established a system of checks and balances against the Konoha Hospital faction within the Headquarters while supplementing the Headquarters' operational capacity. Consequently, the group of people who had previously slacked off by relying on their status as "Konoha Hospital veterans" or "former seniors of the Tennin" quickly fell into line.
At this point—
Talent, funds, and technology were all in place.
The operation of the Technology Development Headquarters was gradually moving onto the right track.
The division of authority under Yu also grew distinct—
Natsu governed the clan on his behalf, managing all major and minor affairs of the Hyūga clan while concurrently serving as the Chief's Secretary at the Headquarters.
Kakuzu took charge of the Headquarters' finances and the management of the Konoha Hospital faction integrated into the Headquarters.
Orochimaru directed the technical departments of the Headquarters, though his projects operated independently from those of Hiruko and Sasori.
Terai, Yamato, and Shin—three subordinates from the Foundation—began taking over Foundation affairs, led primarily by the experienced and senior Terai.
Shiraishi, Matsumoto, and Furofuki—the three Vice Directors of Konoha Hospital—managed Konoha Hospital while dispatching personnel to cooperate with the Headquarters' research.
Once the initial influx of personnel, management, and financial matters were properly settled and a preliminary set of reference rules was established, Yu began gradually delegating his authority—
Not because he found it troublesome, nor because he lacked the ability to manage such a large group of people.
Rather, it was because a shinobi's time was limited.
Pouring finite time into the endless headaches of administrative management would inevitably slow down the growth rate of his individual strength.
After all, put simply, the underlying logic of the Shinobi World still dictated that power reigned supreme.
Under Yu's continuous pushing of the Headquarters' work, a week quickly passed.
March 12th, 9:00 AM.
Headquarters, top-floor office of the Black Tower.
Yu had just finished signing an important document that required his approval.
Dressed in secretarial attire and holding a stack of files, Natsu pushed the door open and entered, bringing good news:
"Lion-kun, word just came from the fourth floor—the theoretical verification of the Chimera Technique has been completed!"
Hearing that, Yu immediately raised his head from the shrinking mountain of paperwork, his eyes lighting up.
"It's finally done?!"
Holding the files, Natsu spoke up: "Hiruko asks that you head down to the laboratory on the fourth floor. He wants to report the results to you in person."
"Additionally, news came from the Foundation. The first batch of intelligence regarding the Land of Wind and Land of Water directions has been sent back and submitted to the higher-ups. It is estimated that the higher-ups will convene a meeting regarding this matter very soon."
"Terai will send over the detailed intelligence shortly. Keep an eye on it."
"Understood."
Yu nodded, immediately putting down his pen, standing up, and walking outside.
Black Tower, fourth floor, Hiruko's laboratory.
The elevator doors opened, and an odor blending culture fluid and disinfectant washed over him.
Hiruko stood at the end of the corridor accompanied by two assistants. Seeing Yu appear, he immediately came forward to greet him.
"Tennin."
Hiruko's voice suppressed a sense of excitement. Dark circles surrounded his eyes, suggesting he hadn't slept much over the past few nights, yet his entire being exuded an intense thrill from the inside out.
He said excitedly: "The first phase of theoretical verification is complete."
Yu nodded, following him into the lab.
The interior of the laboratory was quite cluttered.
The operating tables were covered with Petri dishes, test tubes, and clipboard logs, while the whiteboards on the wall were filled with dense chemical formulas and molecular structure diagrams. A few new pieces of equipment sat in the corner—analyzers and microscopic imaging devices imported from the Land of Lightning by Orochimaru—which were currently humming and producing a soft white noise that wasn't grating to the ears.
"Have a seat." Hiruko gestured toward a chair beside the operating table for Yu, while he himself jogged over to pull a blank whiteboard close, grabbing a black marker.
"I'll explain from a theoretical level first—"
He drew two small stick figures on the whiteboard, labeling them "Hyūga" and "Kaguya" respectively.
"The core problem of the Chimera Technique has never been 'whether it can be fused,' but rather 'how to maintain stability after fusion.'"
Hiruko tapped his pen between the two circles, explaining: "The chakra essence of different Kekkei Genkai is inherently distinct; forcibly fusing them will inevitably cause rejection. Rejection manifests in three forms—"
He listed them underneath on the whiteboard:
"1. Apoptosis; 2. Chakra rampage; 3. Mental collapse."
"Over the past three years, I have been researching how to evade these three forms of rejection." Hiruko turned to look at Yu. "The conclusion is: it is impossible to evade them completely, but through a 'carrier' and a 'formula structure,' rejection can be controlled within an acceptable range."
He pointed at the two circles on the whiteboard, circled them together, and drew a larger circle labeled "Carrier".
"The role of the carrier is to provide a 'buffer zone'—not to simply accommodate two lineages, but to establish a dynamic equilibrium between two chakras, allowing them to balance each other rather than conflict."
Looking at the large circle, Yu seemed to realize something.
"You mean, coexistence."
To put it simply, the Kekkei Genkai fusion of the Chimera Technique wasn't a true fusion, but a form of "coexistence"—coexisting with two or more Kekkei Genkai within a single body, remaining mutually independent and non-interfering without conflicting or running amok.
Hiruko's simultaneous possession of Swift Release, Dark Release, Storm Release, and Steel Release operated on this exact principle.
"Correct." Hiruko nodded.
He walked over to the operating table, pulled out a thick logbook, flipped to a page, and handed it to Yu:
"This is the experimental log from the past two weeks. A total of thirty-seven sets of cellular fusion experiments were conducted—thirty-two failed, and five succeeded."
Yu took the logbook and browsed through it rapidly.
Every set of experiments was logged in extreme detail: fusion time, cell source, culture conditions, timing of rejection reactions, process of cell death, changes in gene sequencing results... The thirty-two failed groups each had their own cause of death—some suffered massive apoptosis within six hours of fusion, some held out for three days only to collapse during division, and some cells were clearly alive yet unable to express any Kekkei Genkai traits.
As for the 5 successful sets, 4 of them were marked with the exact same two characters at the end of their logs: Nue-source.
"Nue?"
Yu was slightly stunned seeing that term.
Very quickly, he recalled—
Nue, also known as the 'Gozu Tenno' project, was a scientific research project led by Tanuki Shigaraki in the Foundation. Yu had participated in it previously and had even created the original 'Nue' through surgery using his own genetic sample.
"Out of the five successful sets, four of them used Nue's cells as the primary strain?" Yu asked.
"That's right," Hiruko said. "That is precisely the purpose of the carrier. Fusing two Kekkei Genkai is packed with risk. My original Chimera Technique also prioritized fusing Steel Release first to enhance bodily strength before attempting compatibility with other Kekkei Genkai. Nue inherently contains your genes, so it doesn't reject the Hyūga's Kekkei Genkai, and with Hashirama's cells boosting cellular vitality, it serves as the best carrier."
Hearing this, Yu furrowed his brow slightly.
Because what he wanted was not coexistence, but... true fusion! Only by truly fusing the genes of the Hyūga and Kaguya could the foundation of the "Hamura Sage Body" be constructed.
Prior to this requirement, Hiruko using Nue's cellular strain was undoubtedly taking an opportunistic shortcut.
Flipping through the experimental logs, Yu's eyes quickly landed on the final experimental file.
"What about the other successful exception?"
Anticipating that Yu would ask this, Hiruko immediately picked up a Petri dish from the operating table and handed it over.
Inside the Petri dish was a small clump of pale teal tissue pulsing slowly in culture fluid, its surface revealing faint, delicate textures.
"This is Fusion Group-032, created entirely using the cells of an ordinary Hyūga clan member and an ordinary Kaguya clan member," Hiruko said. "You can check its state."
Yu took the Petri dish and observed it closely.
That clump of tissue possessed far more "vitality" than he had imagined. With every pulse, a faint halo flared across its surface, its color alternating between pale teal and milky white like a rhythmic pulsation.
"If we only used Nue, it would actually yield a similar effect to using the Foundation's iterated Hashirama cells. But fusing two Kekkei Genkai is extraordinarily difficult; we could only prioritize obtaining results through Nue's cells first before working backward."
Pointing at the tissue inside the Petri dish, Hiruko smiled:
"And the result is this!"
"It's breathing," Hiruko explained beside him. "Not with lungs, but with cells. The metabolic rates of Byakugan cells and Shikotsumyaku cells differ, but this clump of tissue found its own balance point—namely, using a periodic rhythm where the two cell types take turns dominating metabolism."
"Take turns dominating?"
"Correct, look at this—"
Hiruko retrieved a chart displaying two waveforms—one blue and one red—alternating up and down along the time axis.
"Blue represents the activity curve of Byakugan chakra, while red represents the activity curve of Shikotsumyaku chakra. In the successfully fused tissue, these two curves never overlap—when the Byakugan genes are active, the epigenetic expression of Shikotsumyaku goes dormant; when Shikotsumyaku is active, the Byakugan goes dormant."
He pointed at the peaks and troughs on the chart:
"The cycle lasts four hours. Four hours dominated by Byakugan, four hours dominated by Shikotsumyaku. Alternating continuously, never faltering."
Yu stared at that chart, falling silent for a few seconds.
"How was this achieved?"
"Formula structure." Hiruko turned back to the whiteboard and began writing new contents beside the previously drawn diagrams.
It was a complex combination of symbols—incorporating chemical molecular formulas, traditional sealing formulas, and extraordinarily intricate chakra flow structures.
Explaining as he wrote, Hiruko said:
"The traditional Chimera Technique relied on 'forced fusion'—using external force to press two lineages together. This method is simple and crude, but the rejection reaction is violent. It only works on the Kekkei Genkai of ordinary civilians, but once used on the Kekkei Genkai of major shinobi clans, the success rate is basically zero."
He drew an X over the words "forced fusion".
"The core of the New Chimera Technique is 'induced symbiosis'. It doesn't compress them together, but allows the two lineages to find their own rhythm of coexistence."
He pointed at the formula structure he had just finished writing:
"The role of this technique structure is to establish a 'chakra oscillation field' during the initial phase of fusion. Once the two lineages enter this field, they are forced to oscillate their chakra according to a fixed frequency. It is forced at first, but gradually, they adapt to this frequency; then, once the technique structure is withdrawn, they will continue maintaining this oscillation."
"It's like two people walking together," Hiruko offered an analogy. "At first, they need someone shouting cadence to stay in sync, but after walking together long enough, they can maintain the exact same pace without shouting."
"Taking it a step further would mean making a move at the continuously intersecting nodes to achieve true fusion. Of course, that aspect still requires further follow-up experiments."
Looking at the complex formula structure on the whiteboard, Yu let out a long breath.
This was still a bit far from his true requirements, but at least it provided a direction to strive toward.
Yu asked the most critical question:
"So right now, if we directly conduct human experimentation to complete the fusion of two Kekkei Genkai, is there a possibility of success?"
Hiruko's movements paused.
The laboratory fell silent for a few seconds.
"Theoretically, yes." Hiruko put down his pen and turned around. "But there are two problems."
"Name them."
"First, materials." Hiruko walked to another operating table and pulled open a refrigerated cabinet. Dozens of test tubes were neatly arranged inside, each labeled with the word "Kaguya".
"Fusion requires a vast amount of Kaguya clan cells to act as 'anchors,'" Hiruko said, pulling out a test tube and handing it to Yu. "Byakugan cells are inherently passive and require the vitality of Shikotsumyaku cells to drive them. If Kaguya materials are insufficient, we can't find the optimal oscillation frequency—we can only use a sub-optimal plan, and the success rate will drop drastically."
Yu took the test tube, looking at the small clump of grayish-white tissue inside.
"How much is left right now?"
Hiruko gave a bitter smile and pointed to the refrigerated cabinet:
"What you see here is all of it. If used for experimental optimization, it can support at most five to six large-scale fusion tests. But if used directly on a human body—"
He paused:
"It can only be done once."
Yu's brow furrowed slightly.
"What about the second problem?"
Hiruko was silent for a few seconds before saying:
"The success rate."
He walked back to the operating table, pulled a file out from a pile of documents, and handed it to Yu.
It was a densely packed data analysis report, with a number marked in red ink on the final page:
0.3%
"This is the simulated human fusion success rate based on existing materials and technique structures." Hiruko's voice deepened. "This is the optimal result; if the materials run out and we resort to the sub-optimal plan, it will be even lower."
Yu stared at that number without uttering a word.
0.3%.
A three-in-a-thousand success rate, paired with a nine-hundred-and-ninety-seven-in-a-thousand mortality rate.
This was no different from throwing one's life away.
Yu raised his head, looking calmly at Hiruko.
If this was the only result, he didn't consider Hiruko's theoretical verification a success.
Sure enough—
Hiruko paused, knitting his brows, and spoke of another possibility with some uncertainty:
"During the experiments, we discovered that there might exist a method with a nearly one-hundred-percent success rate—and perhaps, it is perfectly suited for you—"
"What is it?"
"To reach... the absolute pinnacle of both the Hyūga and Kaguya!"
————
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