Arai claimed he was there to protect Yubi and Sasori while helping them finish out the mission, but after they returned to the base, he and the two boys were almost completely separated from the rest of the team's operations.
Aside from routine patrols through the canyon to make sure no suspicious targets were lurking nearby, Arai spent most of his time training Yubi personally. As for Sasori, he was largely left to do as he pleased.
"You're a medical ninja," Arai said after another sparring session. "Your chakra has a gentle nature, so mastering other kinds of ninjutsu may be harder for you than it is for most."
"Most shinobi are born with an affinity for a certain chakra nature, and through training, they can draw it out. But that isn't absolute. By the time many of them reach the jonin stage, they can usually manipulate two chakra natures. Even then, their talent, proficiency, and the power of the techniques they use can vary enormously."
"Some people may know several types of ninjutsu, but because of their bloodline or their natural strengths, the other techniques they use will never be especially powerful. In the end, they still rely on the combat style they're best suited for."
They stood on a flat stretch of rocky ground deep in the canyon. A moment earlier, Yubi had gone all out against Arai, only to have a kunai pressed to his throat before he'd even fully understood how the exchange had ended.
As the Third Kazekage's personal bodyguard, Arai was considered powerful even among jonin. He was the kind of elite shinobi who made the gap in ability feel almost hopeless.
"I can't teach you medical ninjutsu," Arai continued, drawing his kunai back at last. "That isn't my field. But because of your chakra nature, if you want to become stronger, you'll need to rely on other methods."
"Wind, fire, lightning, earth, water... those elemental styles don't really suit you. Even if you awaken one of those natures in the future, the power of the ninjutsu you use likely won't be especially high. So you'll have to look elsewhere. Taijutsu. Ninja tools. Special techniques. That kind of path."
Arai smiled faintly. "Medical ninjas are far ahead of ordinary shinobi when it comes to precision chakra control and long-term chakra maintenance. That makes them naturally compatible with puppetry. Granny Chiyo is the perfect example. If you wanted to, you'd absolutely be qualified to become a puppeteer too. You might not reach the very top, but it would still increase your combat strength considerably."
Yubi had already considered all of this long ago.
He understood the relationship between chakra and combat development better than most adults in this world. Tsunade, as a medical ninja, had taken the path of monstrous physical strength and overwhelming close combat. Chiyo, meanwhile, had become a master puppeteer. Both were proven roads a medical ninja could walk.
Seeing the look on Yubi's face, Arai narrowed his eyes. "From that expression, I can tell you have no intention of becoming a puppeteer. What you want to improve is taijutsu, isn't it?"
"Not exactly," Yubi replied with a small scratch at the back of his head. "I train my body mainly to increase my chakra reserves."
Chakra was the fusion of physical energy and spiritual energy. It came from every one of the body's countless cells. To a certain degree, it was naturally tied to physical condition.
"Hmm. That does make sense," Arai murmured, stroking his chin. "At your age, the amount of chakra you have, along with the speed of your mobilization and response, is far beyond your peers."
That was because Yubi had never trained his body in a crude, simplistic way. He wasn't chasing raw muscle or surface-level strength.
He had used breathing methods. He had deliberately trained his internal organs. He had even focused on strengthening the meridians that carried chakra throughout the body.
For shinobi, those meridians were the channels through which chakra flowed. They were also the very basis of techniques like the Hyuga clan's Gentle Fist. Once a pressure point was struck and those pathways were blocked, chakra control fell apart. In that sense, meridians were every bit as important as muscle or bone.
"Did you come up with this fighting style yourself?" Arai asked suddenly.
During the short exchange just now, he had clearly noticed the terrifying sharpness of Yubi's observation. The boy seemed capable of predicting movement, almost as if he were reading the body before it acted.
"I'm a doctor," Yubi said with a laugh. "How should I put it? Because I understand the human body extremely well, I have a kind of instinct for it. By just looking at someone, I can roughly judge their strength, speed, and overall physical condition. In battle, if I keep observing, I can calculate more subtle changes too."
He paused, then added with a modest smile, "Of course, that only works well against people around an ordinary level. Against someone like you, Arai-san, it's basically useless. Truly strong people don't move in ways that can be predicted through simple physical data alone."
In other words, Yubi's so-called data-based taijutsu was still only enough to bully rookies.
And even that description was incomplete. What supported his fighting style wasn't just a doctor's trained eye, but also his understanding of the power system of this world itself. The knowledge in his mind was like a database, pieced together from everything he knew.
Naturally, he couldn't explain that to Arai. There was no way he could say that in his original world, Naruto had only been a story on a screen.
Even so, Arai's eyelids twitched.
"As expected, anyone who can become a medical ninja is extraordinary," he said with a sigh.
"It's not that exaggerated," Yubi replied modestly.
Arai looked at him for a long moment before speaking again. "It seems you already have a clear plan for your future combat style and growth path. In that case, there isn't much more I can teach you in terms of direction. What I can do is help you improve your close combat and battle experience through repeated sparring over the next stretch of time."
His expression turned strangely complicated.
At Yubi's age, Arai had still been thinking about games, pranks, and whatever seemed fun that day. His mind had been full of childish things. He had never once possessed this kind of calm understanding of his future, or this sort of clear judgment about what kind of shinobi he wanted to become.
Compared to that, he couldn't help sighing inwardly. Some people truly couldn't be compared to others.
So this is what they call a genius, he thought.
"Again," Arai said, his tone sharpening.
"Yes," Yubi answered at once.
The next second, Arai vanished.
Yubi tightened his grip on the scalpel in his hand and sank into a defensive stance. Every muscle in his body drew taut, his breathing steadying as his gaze flicked sharply through the empty space around him.
"In fights between shinobi, you can't always trust your eyes," Arai's voice sounded out. "Your senses can deceive you. More often than not, what you need to rely on is the intuition you've built through combat. That includes the perception of chakra. Movement can lie. Release can lie. But the transfer of energy does not."
Yubi's eyes darted once more as he tried to lock onto the source of the voice.
But before he could react, Arai appeared behind him like a ghost.
Smack.
Arai's palm chopped down lightly against the back of Yubi's neck. On a real battlefield, that one clean strike would already have made him a corpse.
Yubi let out a helpless breath. "So strong."
This was what a true elite jonin looked like. No wasted movement. No obvious flaw. No opening he could exploit.
The title elite only really existed among jonin. Genin and chunin had no such distinction. There were also special jonin, shinobi who possessed exceptional talent in one area but whose overall strength was comparatively average. And then there were teacher jonin, those assigned to guide fresh squads or serve at the Academy.
Ninja rank was not always a clean reflection of battle strength. The standards were complicated, and they varied from village to village.
Among all of them, the Five Great Villages naturally held the highest standards. But the village whose system carried the most prestige was still Konoha.
That wasn't because Konoha was the center of the world's story. It was because so many of the structures, rules, and institutions that governed the shinobi world had first been established there. The other villages had simply followed after.
"Again," Arai said.
"Yes."