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"You've already helped me a great deal by stitching the blood vessels and muscles in my arm together." Uchiha Nagi was soaked, as if he had just emerged from water.
Even with many Shadow Clones, each would only have one hand, which isn't as convenient as having two hands working together, and Tamayo's technique was also very skilled.
Uchiha Nagi wiggled his fingers. Although the surgery had just finished, he could already control his fingers, which made him marvel at the incredible nature of white zetsu cells.
He could even feel an intense itch in his bones, muscles, blood vessels, and nerves. This was a sign of rapid cell regeneration, as blood continuously circulated back and forth between his own blood and the White Zetsu arm.
The White Zetsu arm absorbed nutrients and Chakra from the blood, and the cells began to grow wildly, healing the severed arm. He believed that in less than a day, the bones at the severed point would heal, and in three to four days, he would be able to use his arm perfectly normally.
More importantly, there seemed to be an unexplainable substance within the white zetsu cells that was slowly circulating through his body with his blood. His Mangekyo, which had been used for ocular techniques, also felt less fatigued. A cool sensation began to flood his eyes, and even his severely damaged left eye started to recover slowly. He believed it wouldn't take a year to use it again.
"I have already received a reply. Kagaya Ubuyashiki is very welcoming of your joining and invites you to the Demon Slayer Corps headquarters. Please rest for a few days, and once your injuries are healed, you can depart with Tanjiro."
"Understood, thank you very much."
Taking money and solving problems for others—Uchiha Nagi wanted to learn the Breathing Technique of this world, so joining the Demon Slayer Corps to help was perfectly reasonable. Moreover, compared to the Ninja world where he was constantly being attacked by Ninja teams with different abilities, there were far fewer demons in this world.
Most of the time, the Demon Slayer Corps outnumbered and fought the demons. And as long as it was under the sun, he could completely relax and not worry about any sneak attacks.
In the Ninja world, whether you were eating, sleeping, or even playing cards with a woman, you had to worry about being poisoned or ambushed. Especially in Konoha, Uchiha Nagi couldn't feel at ease, with a certain 'pot king' constantly trying to dig out his Sharingan.
Then, Uchiha Nagi, as agreed, began to exchange medical knowledge with Tamayo, explaining the principles of the Mystical Palm Technique. "Chakra? Is this the basic energy required for your miraculous techniques? It's truly amazing. This is the first time I've heard that humans, besides Breathing Technique, also have something called Chakra."
Tamayo exclaimed, "According to your explanation, extracting cells from the human body is similar to our Blood Demon Art, but once we are transformed into demons from human bodies, we probably can't extract the kind of energy you mentioned; we can only use Blood Demon Art."
Uchiha Nagi said, "Blood Demon Art seems to be a technique generated from your genes combined with your own being. Each demon cannot replicate another demon's Blood Demon Art, right? But Chakra can be used to perform all techniques common to humans. However, the specific situation still needs to be gradually verified."
Because no one in this world has Chakra, he doesn't know if they can learn it, so it needs further research.
As for the Breathing Technique, Uchiha Nagi confirmed that he could use it. He had no problem replicating Tanjiro's Water Breathing.
His earth attribute was relatively weak, fire was the strongest, and water, lightning, and wind were moderate, so replicating Tanjiro's Water Breathing Technique was not difficult.
Moreover, if Chakra attributes can be enhanced through development, then why can't Breathing Techniques of different attributes be developed?
Kakashi continuously developed his different attributes, eventually becoming the Copy Ninja. While inherently weak in a certain attribute, later development can strengthen it.
Getting sidetracked, after chatting with Tamayo for a while, Uchiha Nagi came to the surface. Tamayo and her companions couldn't come out during the day, but Tanjiro could.
Tanjiro was continuously practicing his Breathing Technique in the dilapidated yard, combining it with his sword skills to unleash dazzling moves.
After watching for a while, Uchiha Nagi called out to Tanjiro, "Tanjiro, there's something I want to discuss with you."
Tanjiro turned around, sheathed his nichirin blade, and walked over. "Mr. Uchiha, is your surgery finished?"
"It's incredible, you actually have this ability? You can reattach a severed hand?" Tanjiro looked at Uchiha Nagi's reattached hand, marveling.
"Hehe, if you want to learn, I can teach you. By the way, may I observe your Water Breathing? It's an equivalent exchange; I can teach you some other things."
After speaking, Uchiha Nagi formed a hand sign with one hand, creating a Shadow Clone. Then, both clones worked together to form hand signs. After a series of dazzling hand signs, a Water Release Ninjutsu appeared before Tanjiro's eyes.
"Water Release: Water Dragon Jutsu!"
A towering giant dragon made of water soared into the sky, then crashed into and toppled a large section of trees in the forest. This immense display, there was no other word for it—cool.
"Hiss—Sugoi!" Tanjiro's breathing quickened. "That's amazing, Mr. Uchiha! Your Breathing Technique is so incredible, and you can even make clones! Are you really willing to teach me? Oh no, what I mean is, you can learn my Water Breathing as much as you like, and it's fine if you don't teach me your Breathing Technique~" Uchiha Nagi smiled, "I'm only a few years older than you. Just call me Nagi-nii. No need to keep calling me 'Mister' and making me sound old."
"What I use is called Ninjutsu, not Breathing Technique. It requires refining a type of Chakra in the human body as energy to use. This clone is called the Shadow Clone Technique, which is a solid clone. However, I can't guarantee if you can learn it, unless you can successfully refine Chakra."
Tanjiro looked at Uchiha Nagi's Shadow Clone with fervent eyes. Who wouldn't want to learn such an amazing Ninjutsu? If he could summon a dozen clones in every fight against a demon, each with a nichirin blade, then… "Slurp~" As he thought about it, Tanjiro almost drooled.
And that Ninjutsu that could control water also looked so amazing. Don't be fooled by the 'water' in his Water Breathing; in actual combat, there wasn't a mass of water surrounding his body. It was just a type of Breathing Technique combined with sword skills.
"Chakra is a type of energy produced by the perfect fusion of the various component energies controlled by the human body. It is the energy source for performing Ninjutsu, Genjutsu, and Taijutsu."
"And this energy is physical energy, taken cell by cell from the human body's 130 trillion cells. It is also spiritual energy, honed through much training and accumulated experience."
Uchiha Nagi also added the last sentence in his mind: If one cultivates Sage Mode, then one part becomes natural energy.
Sage Mode had always been something he yearned for, but unfortunately, no one could guide him into it. Relying on self-discovery was simply too difficult. Even geniuses like Madara and the Second Hokage couldn't master Sage Mode.
Both of them were close relatives of the First Hokage, who surely wouldn't have kept it a secret. Their inability to learn it only showed that the threshold for Sage Mode was indeed too high.
As for Naruto and Jiraiya later on, they were only half-baked Sage Mode users….