Chapter 230 – The Method
Hyūga Ayaka's experiments required a massive statistical base to be reliable, and Kei fully agreed with her approach.
Taking reckless risks only made sense if the reward justified it. In this case, the potential reward was high—but if there was a safer path, why gamble at all?
Since Ayaka had already cleared things with her clan, she could stay here indefinitely. She disliked the oppressive underground labs, though, so Kei arranged a private room for her in the Konoha Police Force headquarters. The compound was huge, and with Imai Kenta overseeing operations in Kei's absence, Ayaka's living conditions would not suffer.
As for Uchiha Shuu, whose new eyes were still in the process of fusing—there was nothing Kei could do now but wait. He and Ayaka didn't spend their nights in the lab, but Fugaku's people tended to Shuu, monitoring his vitals. All data was reported both to Kei and to Fugaku himself.
After all, these weren't just any Sharingan—these were eyes without the usual chakra depletion, eyes that could rival Madara's in sheer potential. Fugaku, however, silently disapproved of Kei's crude method: literally cramming two pairs of Mangekyō into one person's sockets.
Still, he had made a promise and wouldn't interfere. In truth, part of him almost hoped the experiment would fail, sparing them from a cascade of complications.
Kei, unaware of Fugaku's private thoughts, was only frustrated by the glacial pace of fusion. Ayaka checked daily with her Byakugan, but after a full week she saw no sign the eyes were merging.
If not for Kei sensing faint currents of strange power between the two Mangekyō, he would have called the whole thing off already.
"Looks like I'll have to use Mangekyō power to stimulate and accelerate the fusion," Kei muttered.
At this rate—given Shuu's erased consciousness and the lack of any guiding will—his body was left to instinct alone. By Kei's rough estimate, natural fusion would take at least half a year. Half a year! By then, the Nine-Tails incident would already be upon them. Impossible.
Fortunately, Ayaka's recent progress with cellular medical ninjutsu offered another avenue. She handed Kei a report compiled from his samples and the strange "material" he had provided.
"Your compatibility just scrapes a passing grade," she said flatly. "Out of over a thousand test trials:
~10% showed no reaction at all,
~40% successfully fused,
~28% suffered destructive backlash from the foreign cells."
Kei frowned. "Not good enough. Is there a way to suppress the devouring effect? Or at least shift the odds—more null reactions, fewer backlashes?"
Forty percent wasn't terrible, but the nearly thirty percent chance of violent rejection was unacceptable. So much for "side-effect-free Hashirama cells." For someone like Danzō, perhaps, that would count as success. Danzō didn't care how many subordinates died, and had no shame using them as fodder.
Kei thought grimly of Yamato. At the time of his childhood experiments, Tenzo hadn't even received Hashirama's cells yet. The real transplantation likely happened later—around the time of the Uchiha massacre—otherwise how could Danzō so casually stuff a Mangekyō into his own socket and survive?
Madara, too, had gambled on Obito—merely because the boy collapsed near him, conveniently a fellow Uchiha. For Madara, grafting half a body of Hashirama cells onto Obito was considered a favor. If Obito survived, great—another weapon. If not, so what? It only proved that only Madara himself could truly master Hashirama's power.
Ayaka shook her head. "It's troublesome. The test cells you gave me… their vitality is monstrous. I've never seen such activity. Their durability is hundreds, maybe thousands of times that of normal human cells. What are these?"
Kei's expression didn't flicker. "Not something I can tell you—yet. If the experiments succeed, I'll share. For now, focus. You said it's troublesome. That means you do have a solution, right?"
Ayaka nodded. "An option exists: external fusion. Merge your cells with the samples outside your body first. Once a stable hybrid cell line is produced, we reintroduce it into you. But…" She paused. "The efficiency is abysmal. And your body might reject them anyway."
"External fusion, then re-injection," Kei echoed, brow furrowing.
Yes, that would improve safety. But the scale was insane—tens of trillions of cells in a human body. Replacing even a fraction this way could take a lifetime. Worse, rejection meant many of the new cells might die off immediately, wasting the effort.
"What's the maximum safe dose at once?" Kei asked.
"I can try for larger batches if we use blood as the medium," Ayaka replied after a moment's thought. "That might improve integration—but also increase rejection. Still, once you survive the first round, each successive batch will be easier. Your body will gradually accept the newcomers."
Kei exhaled slowly. "Fine. We'll try it your way. One step at a time."
Ayaka's eyes softened, though her tone stayed cold. "Then once a week. No more often. And I'll be observing closely."
Before Kei could thank her, she added, "Don't mistake this for kindness. My position hasn't changed. Helping you helps me. That's all."
Kei chuckled. She was right: manipulation wouldn't work on him, so she'd chosen equal exchange instead. And she was useful—useful enough that Kei was already considering what to trade in return.
Not yet. Not until the time was right. But one day, he would share certain secrets with her.
Like the hidden pathway on this continent… the one that led straight to the moon.
Kei also needed to forge evidence—artifacts with a convincing sense of "ancient history" that could support the claim: the Hyūga clan originally came from the moon.
Only after preparing such things thoroughly would Kei reveal them to Ayaka. Then, guided by those "discoveries," she could begin her search. By the time she uncovered that hidden place, Kei's eyes might already have reached their full strength.
The Tenseigan itself was of little direct use to Kei. The Sharingan already had its own path of evolution—no need for the same complicated detours.
But as bloodlines both traced back to the Ōtsutsuki clan, there was still much worth studying. The massive Tenseigan sealed on the moon, brimming with terrifying power, was enough to pique Kei's interest.
After nodding in agreement with Ayaka's proposal, their first experimental trial officially began.
While Kei was beginning his own self-experimentation, elsewhere in the village an entirely different storm was brewing.
Inside a dim office sat four figures—Sarutobi Hiruzen, Koharu Utatane, Homura Mitokado, and Shimura Danzō. For decades, these four had been the hidden architects of Konoha's political foundation. Even now, they remained its true powerhouses.
"Orochimaru has gone too far," Danzō growled, slamming a report onto the table. His expression was as dark as ink. "If my people hadn't uncovered this, we'd never have known his base was even under investigation. We asked him, and he gave us nothing. Hiruzen, this is your precious student?"
Hiruzen's eyes narrowed, his voice heavy with restrained fury. "Don't you dare put this solely on me, Danzō. If not for you, how would Orochimaru have gotten involved in such forbidden research in the first place? And if not for your meddling, how would his secrets have ever been exposed? Do you expect me to believe your hands are clean? Do you take us for fools?"
"Enough, both of you," Koharu said wearily, pinching the bridge of her nose. "You've been at each other's throats for years. Hiruzen is no longer Hokage—must you still quarrel like this? We have far more pressing matters."
Homura exhaled slowly, his voice carrying the weight of long service. "She's right. The past is done. What we must discuss now is Orochimaru… the Fourth Hokage… and the Uchiha."