Cautious Eyes: An Uchiha's Path

The four giants of Konoha were entangled in subtle power games, their quiet maneuvering aimed at controlling the direction of the village—and particularly, at containing the influence of the Fourth Hokage. Meanwhile, deep underground, Uchiha Kai was immersed in his own dangerous ambitions.

After Aya Hyuga extracted 4,800 milliliters of Kai's blood for cellular experimentation, it had taken him some time to fully recover. Still, Kai showed little concern for the toll it took on him. He was focused on the in vitro fusion experiment Aya had proposed—one designed to merge fragments of Uchiha and Senju lineage at the cellular level.

But it was more time-consuming, and more difficult, than either of them had expected.

Nearly two weeks passed before the first viable experimental materials were ready. Unfortunately, the results were worse than the last trial. The failure rate hadn't increased, but the rate of cellular engulfment had. The modified cells were being consumed or rejected at a higher rate than anticipated.

Kai frowned slightly. It wasn't a good sign.

"I guess I'm lucky I'm not as reckless as Obito's brat," Kai muttered. "Otherwise, I'd probably have turned pale white by now, maybe even started growing branches like those White Zetsu clones."

Disposal of the failed samples took another two days, and only a tiny amount of usable material remained—less than 200 milliliters of viable sample from the original 4,800 milliliters of blood.

"The important thing now is whether these fused cells can survive in my body," Kai said, his voice low. "And more importantly... whether I can survive them."

He knew his body might reject the altered cells. Worse, there was the risk that they could destabilize his chakra system. After all, these were no longer pure Senju cells—they had been fused with Kai's own Uchiha cells. The quantity was also too small to make a meaningful impact immediately. A drop in the ocean, really.

Cell fusion was proving far more difficult than anticipated.

But there was a silver lining.

The fusion of Osamu Uchiha's Mangekyō Sharingan with that of Yuji Uchiha had made visible progress.

It was Aya who had discovered it. Even with the thick gauze covering Osamu's eyes, her Byakugan had detected the subtle shift. The two pairs of Sharingan were beginning to resonate, to sync. The fusion process was still early—no more than 5% complete—but the ocular tissues were already merging on a fundamental level.

According to Aya's report, the two eyes had not shown signs of rejection or degeneration. Instead, they were being drawn together by a unique, internal force—one that appeared to be natural, rather than artificial. It was the most promising result yet.

"Do we have a full diagnostic report?" Kai asked, glancing at Osamu, who lay unconscious on the chakra-monitoring array.

"Yes," Aya replied. Her tone was cold and professional. "Genetically and ocularly. Which do you want to hear first?"

"Let's start with the worst of it," Kai said. "I prefer to hear the bad news first. Makes the good easier to enjoy."

Aya gave him a sidelong glance. "You may be disappointed. There's not much bad news this time."

Kai blinked. Then, despite himself, a smile flickered at the corners of his lips.

"All good news?" he asked.

Aya nodded slightly. "Your hypothesis was correct. The genetic data from Osamu, cross-referenced over the past few days, confirms it. The fusion between the Mangekyō Sharingan of Osamu and Yuji has started producing an entirely new energy."

Kai's eyes narrowed.

"It's similar to chakra," Aya continued, "but not exactly the same. It's denser. More... refined. Under its influence, new cell types are emerging within Osamu's body."

"You can see them?" Kai asked, surprised.

"They're unusually active. Not because my Byakugan has evolved, but because these cells stand out. They seem to carry a unique signature—a strange, potent energy."

Aya went on to explain that these cells appeared to stimulate dormant segments of Osamu's genetic code. Previously inert regions were now showing reactivity, as though something inside had been reawakened.

"In fact," she said calmly, "it appears that Osamu Uchiha's genetic chain is incomplete. There are distinct signs of fragmentation at the start of his DNA strands."

Kai raised an eyebrow. "You're sure?"

Aya nodded. "It's just my observation, and I only have one subject to go off of. But yes—I saw the break marks clearly."

It wasn't unexpected. Kai had long theorized that the Uchiha bloodline had diverged from the original Ōtsutsuki lineage. The split between Indra and Asura, the sons of the Sage of Six Paths, had fractured the once-unified gene pool. The Hyuga clan had retained more of the original structure, while the Uchiha had evolved—possibly even mutated.

"You compared it with mine, didn't you?" Kai said quietly.

"I did," Aya admitted. "And with Yuji's. But I couldn't detect the same marks. Your genes are… hidden, somehow. Shielded. Which is why I raised the issue."

"I'm not blaming you," Kai said, shaking his head. "You're being thorough. Just let me know next time before you take a deeper look."

Aya dipped her head in acknowledgment. "I understand. Still, it confirms one thing—you're not average. And neither is what we're dealing with."

Kai sighed. "Neither are our problems."

He was silent for a moment, thinking. Their cooperation was dangerous and unconventional. But Kai had made their relationship publicly visible—he had arranged for Aya to join his team in the open, to even have dealings with the Hyuga clan elders. If anything happened to her now, he would be implicated. That, in its own way, was a form of protection.

Aya had proven her value.

Despite her lack of formal training in medical ninjutsu, her Byakugan, her intelligence, and her Hyuga blood gave her a unique advantage when it came to understanding chakra pathways and genetics.

"It seems your family genes are still superior in some ways," she said suddenly, giving him a measured look.

"There are… ways to address our shortcomings," Kai replied. "Speaking of which—can we extract that special energy from those fused eyes?"

Aya shook her head. "I doubt it. Whatever it is, it behaves like chakra but doesn't fully conform to it. I lack the sealing techniques to isolate it."

"Figures," Kai muttered. "It's probably similar to Yin chakra—the emotional imprint found in Mangekyō Sharingan abilities. Difficult to extract or replicate."

Still, he wasn't about to give up.

"Is it embedded in the cells?" he asked.

"Yes," Aya confirmed. "The energy itself can't be isolated—but the cells that generate it can be harvested. Even if they're few in number, it's better to study the source than chase the byproduct."

Kai nodded slowly. "Then continue the experiments. Let's start with another round of in vitro testing."

It was their only path forward now.

Kai hadn't expected the Eternal Mangekyō to offer more than vision and power, but now even its cellular byproducts were of value. He had asked Aya to study medical cytology to analyze White Zetsu cells—but it turned out that the Eternal Sharingan's fusion produced something just as intriguing.

And just as dangerous.