Chapter 233 – An Unexpected Discovery
Uchiha Kei had to admit—he'd struck a good bargain.
A Hyūga with the Byakugan, Hyūga Ayaka, was solving problems that had stumped him for months.
Reliable, meticulous, and sharp, she'd proven her worth many times already.
After only a few days, Ayaka placed another report into his hands.
During that time, Kei had resisted the temptation to use the serum created by fusing his own blood with White Zetsu's cells. He wanted clearer, more detailed data before taking that risk.
"The report's ready," Ayaka said. She looked tired, but her eyes still gleamed with focus. "It's not an encouraging outcome. Out of a thousand test samples, there were only two meaningful results. You'll want to brace yourself."
"Only two results?" Kei frowned, then absently waved away a fly buzzing overhead. Irritations could wait—his full attention had to be on this.
He lowered his gaze to the report… and his face darkened.
The results were brutal:
20% of the cells fused successfully.
10% showed no reaction.
A staggering 70% triggered severe rejection.
No wonder Ayaka had said there were only two outcomes. Ten percent could be dismissed as negligible; the rest painted a grim picture. The experiment was practically a failure.
"Why… why such a ridiculous failure rate?" Kei muttered, brows knitted.
"Because those cells are on a higher tier than yours," Ayaka replied evenly.
"And beyond that—they don't match you. Or more precisely, they don't match your eyes. They were activated by another pair of Mangekyō Sharingan."
Another pair of eyes… Kei exhaled slowly. Now it made sense.
That explained why non-blood relatives could never create an Eternal Mangekyō together.
It wasn't that fusion was impossible—it was that the power born from such fusion didn't harmonize with the host's genetic and ocular imprint.
The result? Failure. High-grade cells devoured the weaker ones, growing unstable. Kei's body, unable to recognize them, would attack back—triggering vicious rejection.
The consequences were catastrophic.
At best: blindness.
At worst: total collapse and death.
Even Kei couldn't gamble on odds like that.
Strictly speaking, White Zetsu's cells were also "higher grade," but they had shown a reasonable success rate in merging with him. They caused side effects, yes, but only low-level ones.
These new cells? Their backlash was violent—unacceptable.
Kei shook his head, a bitter taste in his mouth. I came this far… only to hit a dead end?
The experiments so far had been a mix of good news and bad—always within a tolerable range. But this outcome practically declared the project a failure.
Even the few "successes" weren't viable; it would take a lifetime of painstaking fusions for them to matter. He couldn't afford that.
"So… I was dreaming after all." Kei let out a wry laugh. "Without close-blood Mangekyō to guide the process, trying to overcome high-grade cell devouring was pure fantasy. I thought I'd found a new key…"
"Sorry," Ayaka said quietly. She understood his frustration, though comforting him wasn't in her nature.
Kei crumpled the report into a ball and tossed it into the bin. He turned to leave—then froze mid-step.
High-grade cells…
White Zetsu's were high-grade.
So were the cells birthed from the Mangekyō fusion.
But White Zetsu's had already merged successfully with his own.
What if I used those fused cells as an intermediary?
He turned back toward Ayaka, eyes sharp.
"What if… I took the stable fused cells from my White Zetsu experiments—and merged those with these?"
"You mean secondary fusion, then reinjection?" Ayaka blinked, then began thinking it through seriously.
After a long pause, she raised her head. "I can't guarantee anything. There's no precedent. But theoretically… it's worth trying."
Her reasoning was clear:
The rejection stemmed from two problems: the cells' higher tier, and their mismatch with Kei's ocular imprint.
The second issue was unsolvable. But the first… perhaps not.
The White Zetsu material Kei had given her was incredibly high quality—in some ways, even superior to the cells extracted from Uchiha Shuu.
If those Zetsu-based hybrids were already accepted by Kei's body, using them as a bridge could suppress the violent rejection while retaining the Mangekyō-derived traits.
That way, even if side effects arose, they'd likely be mild, not catastrophic.
Ayaka's voice stayed calm, but there was a glimmer of curiosity in her tone:
"In theory… it might work."
Hyūga Ayaka thought it over carefully. Yes… this might actually work.
"Then let's try it." Uchiha Kei clenched his teeth, eyes steady. "We've come this far—if I don't at least attempt it, I'll never forgive myself."
"No problem. I've just extracted a new batch of cells today—we can start right away." Ayaka nodded. "But what about the leftovers from your earlier trials?"
"Throw them in as well," Kei said decisively. "No point wasting them. If separating them is too much trouble, I don't mind discarding them."
"It'd take days to separate, so we'll abandon those for now." Ayaka tapped her chin in thought. "I can begin immediately. It's a shame, though. If this fails, all that blood will be wasted."
Kei felt a flicker of guilt—Ayaka had poured days of effort into this. But she seemed unconcerned. Waste was tolerable, as long as it improved the reliability of the results.
She retrieved the vial of Kei's previously stabilized serum from the freezer, thawed it carefully, and began the new experiment.
Kei could only watch. In such matters, he was little more than a bystander.
Flies buzzed overhead again, irritating him. This underground lab was nothing like Orochimaru's pristine facilities—humid, poorly ventilated, prone to vermin. That snake had the village's backing, with limitless funding for infrastructure. Kei, on the other hand, was working in what was once just his old hideout, clumsily expanded.
And somewhere nearby… a corpse probably still remained. Uchiha Yuu's body. Kei had never asked how Ayaka disposed of it. Some things were better not dwelled on.
He waited in tense silence as Ayaka worked. To his surprise, the procedure went much faster than expected. Barely an hour later, Ayaka turned toward him with an odd expression.
That look made Kei's stomach twist. He suddenly felt like a student awaiting exam results.
"I have to admit… your luck is extraordinary," Ayaka said at last, gazing at the vial before sighing softly. "The fusion rate hit seventy-seven percent. The rest weren't even real failures—Uchiha Shuu's cells were simply consumed, resulting in neutral reactions."
"Seventy-seven?" Kei's eyes widened. A rare look of disbelief crossed his face. "That high? And no complications?"
"You don't need to doubt my conclusion." Ayaka shot him a glance. "If you're skeptical, we can repeat the trials. It'll take longer, but it would be safer."
"What exactly happened?" Kei asked, unable to tear his gaze from the blood sample.
"Your cells and the white material's cells fused together, creating something of a higher tier. Being both advanced cells, they interacted and produced a faint but distinct new force. Subtle, but I could sense it. That force drew them to one another until they merged completely."
"A new force… pulling them together into one," Kei whispered. A shiver ran down his spine. So this is it… a real way forward.
He took a deep breath, steadying himself. Then, with a voice as calm as he could manage, he asked:
"If I inject this back into my body—what happens? Does your earlier conclusion still hold?"
"Yes," Ayaka said after a pause. "Negative reactions are inevitable. But since part of these cells already originate from you, your body should adapt to them well enough. The integration rate will be far higher."
"…I see." Kei nodded slowly, a faint smile tugging at his lips. "Then this counts as a success after all."