Arai had said he would protect Yubi and Sasori while they completed their mission, but after returning to the outpost, he took the two of them and broke away from the squad's operations entirely.
Aside from patrolling the area each day to check for suspicious targets, Arai spent most of his time guiding Yubi's training.
As for Sasori... he was left entirely to his own devices.
"You're a medical ninja, and you can use Medical Ninjutsu. At present, your chakra's nature transformation is gentle and belongs to Yang Release. So... learning other types of ninjutsu will probably be harder for you."
"Most ninja are born with a particular chakra nature, which they can learn to use quite easily as they grow... but that isn't absolute. By the time they reach Jonin, most can perform two chakra nature transformations... but knowing how and being proficient are different things, and the power of their ninjutsu varies from person to person, too. For some people, even if they master several chakra natures, their bloodline means that any ninjutsu outside their inherited chakra nature may have very limited power... so even if they know multiple types of ninjutsu, they rarely use them within their established fighting style and patterns."
On a patch of ground in the canyon, Arai and Yubi had just finished sparring.
As the Third Kazekage's personal guard, Arai ranked among the stronger Jonin.
He was an Elite Jōnin.
So even when Yubi gave it everything he had, he could gain no advantage.
In the blink of an eye, Arai had a kunai pressed against his neck.
"I can't guide you in Medical Ninjutsu. It isn't my strong suit, after all... but as a medical ninja, your chakra nature means you'll have to rely on other methods if you want to grow stronger. Wind, Fire, Lightning, Earth, and Water Release aren't particularly suited to you... even if you master one of those natures in the future, your ninjutsu won't be very powerful. So you can only put your effort into Taijutsu, ninja tools, and other ninjutsu... medical ninja far surpass other ninja in controlling and sustaining chakra, which happens to fit a puppeteer's requirements perfectly. Just like Granny Chiyo, if you wanted to, I believe you have everything it takes to become a puppeteer. Even if you couldn't reach the very top, it would be enough to improve your strength."
Arai smiled as he spoke.
In fact, Yubi had already considered everything he mentioned.
He also understood the factors involving chakra very thoroughly.
Tsunade, for instance, relied on devastating Taijutsu and physical strength as a medical ninja.
Chiyo relied on the Puppet Technique.
Both were paths a medical ninja could take to advance.
Watching Yubi's expression, Arai said, "From the look of you, you don't seem to be planning on becoming a puppeteer... what you want to improve is your Taijutsu, right?"
Even after only a few exchanges, Arai's discerning eye could tell that Yubi had trained and honed his body through painstaking effort... he clearly intended to pursue Taijutsu.
Yang Release was a manifestation of the vitality of flesh and blood.
"Not really... I only train my body to increase my chakra reserves." Yubi scratched his head and explained with a slight smile.
Chakra was the life energy of the body and mind, originating in the body's 130 trillion cells. To a certain extent, it was also closely linked to stamina.
"Hmm... true. For someone your age, both your chakra reserves and the speed at which you mobilize it and respond are far beyond your peers."
Arai stroked his chin as he offered his assessment.
That was because, when Yubi honed his body, he did not simply pursue strength or muscle. He used breathing exercises to deliberately train even his internal organs and chakra pathways.
For ninja, chakra pathways were the "channels" through which they mobilized chakra... they were also the foundation of the Hyuga Clan's use of the Byakugan to strike chakra points. Once those points were struck, an enemy's ability to use chakra could be cut off.
Thus, chakra pathways were also extremely important to ninja.
"Did you develop this kind of Taijutsu yourself, too?"
Arai asked another question.
During their exchange just now, he had distinctly noticed Yubi's remarkably fine powers of observation. He seemed capable of predicting Arai's movements... it was rather impressive.
"I'm a doctor... how should I put it? Since I know the human body very well, just think of it as a kind of natural intuition. With one look, I can more or less estimate someone's physical strength, speed, and other attributes. During a fight, I can also pick up on subtle physical details and use them in my calculations. Of course, this kind of Taijutsu only works against fairly average opponents. Against someone like you, Mr. Arai, it's completely useless. Because when someone is strong, there's no way to predict how he'll perform in battle through something as simple and superficial as physical data."
Yubi smiled as he spoke.
In other words, his Data Taijutsu could only handle novices.
There was also the fact that... his Taijutsu relied not merely on a doctor's intuition, but purely on his understanding of this world's system of power.
In other words, the database in his head.
Of course, he could not tell Arai that.
He could hardly say he had transmigrated from another world, where Naruto was only an anime...
"Hiss."
Still, his words made Arai's eyelid twitch.
"Sure enough, anyone who can become a medical ninja is no ordinary person..." Arai remarked with a sigh.
"It's really not that impressive."
Yubi was modest.
"It seems you have a clear plan for your fighting style and the direction of your growth... in that case, there isn't much I can teach you. The only thing I can do is spar with you over the coming days to improve your Taijutsu and practical combat experience."
Arai's gaze grew somewhat complicated.
At Yubi's age, he had still been thinking about having fun... he had still been a child at heart.
His thinking had been nowhere near this mature, and he had possessed no clear understanding or judgment regarding his future.
The comparison left Arai sighing. Sometimes, people really could not be compared.
So this was what they called a genius...
"Let's continue."
Arai's tone turned serious.
"Yes."
Yubi nodded.
Then Arai's figure flickered and vanished from Yubi's sight.
Yubi gripped his scalpel and took a fighting stance.
"In a fight between ninja, sometimes you can't judge by your eyes alone, because your senses may deceive you... so more often, what you have to rely on... is the intuition developed through combat. That includes sensing chakra... the transfer and release of energy won't lie."
Yubi's eyes shifted as he readied his defense.
But in the next second, Arai appeared behind him, offering that reminder as he did.
Yubi had failed to detect any trace of his movements.
Smack.
Arai swung a hand into the back of Yubi's neck. Had this been a battlefield, Yubi would already have been a corpse.
"So strong."
Yubi sighed.
So this was an Elite Jōnin... he could not spot even the slightest opening.
And the designation "elite" only existed at the Jonin level. There was no such term for Genin or Chunin.
There were also Special Jōnin... Jonin with special talents in a particular area, but relatively average overall strength.
And Jōnin Instructors... that title referred to those who had to hold a post at the Ninja Academy and have led a rookie squad.
A ninja's rank was sometimes determined by more than strength. The circumstances were rather complicated.
For instance, each village had different standards for assessing ninja ranks.
Among them, the Five Great Shinobi Villages certainly had the highest standards, but Konoha's ranks undoubtedly carried the most weight.
That was not because Konoha was this world's main stage, but because many of the Shinobi World's systems and rules had first been established by Konoha, with the other villages merely following suit afterward.
"Again!"
"Yes."