It turned out Kakashi was overthinking things, trying to figure out the formula himself.
Not just him, but even the more specialized attending physician was completely clueless. Kakashi's blood showed no difference from an ordinary person's, and cell samples taken from his wounds died immediately. There was nothing to indicate how this boy possessed such powerful regenerative abilities.
It was as if the silver-haired youth had a separate set of organs dedicated solely to maintaining his body, ones that simply couldn't be observed directly with current equipment. Their existence could only be inferred through the effects they exerted on his other internal organs.
Proposing a mutually beneficial arrangement to gain the other party's agreement – this was often the best way to protect a secret when interests aligned.
Kakashi offered his own cells to this attending physician, agreeing to share research findings, on the condition that the doctor revealed absolutely none of Kakashi's physical information to outsiders – like the Raikage, for instance.
As for how this deal came about, it started when the attending physician produced the training method for the Eight Inner Gates and charts detailing all the human body's chakra pathways.
After the doctor, radiating an aura that screamed "I am dangerous," revealed his true name – "Shinnō" – and traded a blow with Kakashi that unleashed enough force to shatter all the glass in the room, the silver-haired youth acknowledged that Shinnō was qualified to make a deal with him.
"For a remnant of the Land of Sky to survive until now... you're not bad."
"And the son of the renowned White Fang of Konoha, Sakumo Hatake, becoming a shinobi of Kumogakure in the Land of Lightning? That's quite a surprise to me as well," Shinnō replied.
The white-haired man with deep nasolabial folds showed no surprise when Kakashi stated his real name. It seemed he already knew "Terumi Nishi" wasn't Kakashi's true identity. He slid the half-drawn scalpel back into its pouch and casually tossed the bag onto a nearby table.
It was a gesture indicating he meant no harm, for the moment.
Likewise, Kakashi halted the Sound Binding Genjutsu he had begun casting and accepted the research data on his own body that the man handed over.
Judging solely by the subtle shift in the boy's expression as he took the documents, Shinnō deduced he was an absolute layman when it came to medical ninjutsu.
Kakashi had no intention of pretending to understand what he didn't. What was the point of sharing research findings if he couldn't comprehend them?
"Is there a simpler explanation?"
"This is the simplest explanation already," Shinnō stated. "So far, the research data on your body shows no difference from a normal shinobi's. Even if there are differences, I haven't found them yet. However, your soul's power is abnormally strong. Stronger by dozens of times compared to the ninja with the most potent soul I've ever studied."
"Soul power? You can research that?"
Ninjutsu dealing with the soul was something only a mere handful across the entire shinobi world could master. There was Dan Katō, famed for his Spirit Transformation Technique before his death; the Rinnegan's ability to extract souls and the Samsara of Heavenly Life Technique; and the Dead Demon Consuming Seal – all S-rank techniques of immense power.
After all, not just anyone could mount a defense on the soul level.
"Soul power might be unfamiliar to others, but not to me," Shinnō said, his height slightly exceeding Kakashi's current stature. He leaned closer, forcing the silver-haired boy to tilt his head up slightly to see his expression clearly.
"I once believed the soul could grant eternal life, but I failed. Only the union of body and soul can stave off death. Do you know why?"
"Hm?"
"Because the soul strength of most people in this world is remarkably similar. This holds true for everyone I've studied, including myself. It means that training the soul is impossible; its strength is predetermined at birth. An adult's soul isn't necessarily stronger than an infant's. What people perceive as 'strength' is merely mental fortitude or immunity to physical pain. No amount of physical training can enhance the soul in any way."
"Negative emotions can also grant power, converting into something akin to chakra," Kakashi interjected.
"It seems you know quite a bit."
"But that has nothing to do with the soul," Shinnō countered dismissively.
Kakashi typically avoided these "I'm the expert, you know less than me" types of conversations. They were an obvious display of weakness; being crushed by a disparity in knowledge was also a demonstration of power.
"I am intensely curious," Shinnō continued, his eyes gleaming. "How can your soul be strong enough to influence your physical body, forcing it to produce more chakra?"
"My chakra reserves aren't that large."
"In terms of total volume, that's true. But based on your body's normal development potential, your original chakra capacity should be about one-fifth of what it is now."
"Five times more?" Kakashi murmured, surprised.
"You don't possess a Kekkai Genkai. How did you achieve this? That's why your soul caught my attention."
"You seem to have studied me quite thoroughly in such a short time?"
"It wasn't short. Four days."
A suspicion arose in Kakashi – perhaps his four-day slumber was also this man's doing? How else could he have been unconscious for so long? He hadn't considered it before, but the questionable points were piling up.
"You bastard..."
"Through you, I see hope once again for achieving eternal life through the soul. But I'm not foolish enough to abandon my ongoing research into physical body development."
"Very wise. I am unique."
"Indeed. You must understand why your soul possesses such strength. Can you satisfy my curiosity?"
"No comment."
With that, Kakashi turned, intending to head back to his hospital room. Standing before someone who had studied his body filled him with an urge to punch them.
"That little girl... I studied her a bit too," Shinnō added nonchalantly.
In the blink of an eye, Kakashi attacked without warning. His right hand, crackling with the Raikiri, clamped around Shinnō's neck, slamming him against the wall.
Despite the Raikiri being pressed against his throat, Shinnō remained unnervingly calm. The wound, though cleanly cut, healed rapidly. He had dodged the fatal spot; a wound like this could be healed in a single breath thanks to the regenerative power of his dark chakra.
The muscles on Shinnō's body bulged, transforming the once gentle, scholarly doctor into a burly, bearded figure. An ominous chakra instantly enveloped the entire room, severely restricting the silver-haired boy's sensory range.
"Her bloodline is quite good," Shinnō stated calmly, despite the Raikiri inches from severing his neck. "No need to get so agitated. That 'study' was merely the standard blood test upon admission."
"I wasn't blind to you dodging that strike to your neck just now," Kakashi retorted, his voice laced with chakra that made Shinnō take notice.
"Impressive genjutsu," Shinnō thought, recognizing the subtle manipulation.
"Withdraw your technique. Someone's coming from downstairs," Kakashi said tersely.
Shinnō's body reverted to its normal appearance. Kakashi slowly released a tense breath.
They parted on bad terms. Though their initial contact resulted in a cooperative agreement, neither trusted the other. Only the verbal contract held their fragile alliance together.
"I'll provide you with more of my blood," Kakashi stated as he reached the door. "I hope you can produce some results."
After the boy left, Shinnō mulled over the threatening surge from Kakashi's soul – that momentary wave of power that felt like being plunged into the dead of winter.
«That level of strength... is he truly someone of this world?»
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