With Hatake Sakumo's help, both of them quickly managed to use their new ninjutsu.
Kakashi in particular found this genjutsu child's play. It was far too simple.
The same went for Yuzuru. After just three or four attempts, he successfully used the Water Prison Technique, leaving even Hatake Sakumo marveling at his talent.
The Water Prison Technique was not as simple as merely releasing chakra. Compared with ordinary C-rank ninjutsu, it added the difficulty of controlling the water's flow.
Although Yuzuru still could not control it perfectly, and casting a perfect Water Prison Technique took him a long time, the fact that he could succeed entirely on his own was already proof of his talent.
"Dad, teach me another ninjutsu. I want to learn a C-rank ninjutsu too."
Seeing Yuzuru learn a C-rank ninjutsu so quickly, Kakashi naturally refused to fall behind.
"Lightning release ninjutsu tend to be quite powerful. Kakashi, you need to learn how to control your chakra better first, or you'll hurt yourself."
Looking at the two little ones before him, Hatake Sakumo understood that ordinary standards did not apply. After all, both of them were geniuses.
"Come with me. There's still time today, so I'll teach you how to control your chakra better."
With that, Sakumo led them to the foot of a large tree beside the training ground.
Then he walked straight up the trunk as though it were level ground. His body was parallel to the ground and perpendicular to the trunk, yet he remained perfectly steady. Had Newton witnessed this, he might well have thrown open his coffin and risen from the dead.
Finally, Hatake Sakumo attached the soles of his feet to a thick branch and hung upside down in the air, looking at the two before him.
"That's amazing!"
Kakashi's eyes instantly widened.
"Give it a try yourselves. Attach chakra to the soles of your feet and slowly climb the tree. Once you can stay as steady as I did without falling, you'll have completed it."
Sakumo came down from the tree and habitually rubbed Kakashi's head.
"All right! My turn!"
Kakashi eagerly went to try, while Yuzuru took his time, first attempting to attach chakra to the soles of his feet.
Before long, Kakashi fell to the ground after barely taking two steps.
For an energetic child, control was clearly the hardest part. After all, even self-control was a problem for children.
Geniuses were different, though. After falling just five or six times, Kakashi gradually found the knack, getting farther with each attempt.
Yuzuru began trying too, and their progress was practically neck and neck. Before dark, both had successfully walked up to the branches, but the final step of hanging upside down from a branch proved extremely difficult.
Hatake Sakumo did not leave either. He simply watched his two little boys quietly.
"All right, it's getting late. Time to go home and rest. I can stay home for a week this time, so take it slowly. There's no rush."
"Yes!"
Hearing Sakumo's words, they stopped practicing and followed him home to eat and rest.
After returning to his room, Yuzuru did not hurry to sleep. Instead, he held out his hand and felt his chakra.
A kekkei genkai was a kekkei genkai precisely because the ability existed within one's genes, but whether it could be awakened depended on each person's talent.
Not every member of a kekkei genkai clan could successfully awaken their kekkei genkai.
Fortunately, Yuzuru did not need to deliberately do anything. His chakra naturally began to change.
The water and wind natures merged in a particular way, then became a stream of chakra filled with cold. Even the surrounding air began to frost over.
This was the Yuki Clan's innate ability: Ice Release!
Seeing this, he breathed a sigh of relief.
At the very least, having a kekkei genkai made him far stronger than ordinary ninja.
In the original Naruto world, Ice Release had not stood out. It was merely a kekkei genkai stronger than ordinary ninjutsu. But to Yuzuru, who came from the twenty-first century, Ice Release's potential was no lower than Wood Release's. In fact, it could only be stronger.
After withdrawing his chakra, Yuzuru lay down in satisfaction and began considering his future direction.
Ice Release was not simply about making ice. Strictly speaking, it lowered temperature, and what he needed to do was lower that temperature further.
"Looks like things are going to get very interesting."
With his worries over his kekkei genkai gone, Yuzuru was completely at ease and drifted peacefully to sleep.
Over the following days, Yuzuru and Kakashi worked hard to grow stronger under Hatake Sakumo's guidance.
In less than two days, both had completely mastered Tree Climbing and Water Walking, considerably improving their chakra control.
Yuzuru, who had already learned the Water Prison Technique, also successfully learned his second ninjutsu, a very common wind release ninjutsu: Wind Release: Great Breakthrough!
Kakashi learned a B-rank ninjutsu and a C-rank ninjutsu: Lightning Release: Earth Flow and Earth Release: Headhunter Jutsu, respectively.
As for why he could learn Earth Release, once chakra control improved, different ways of circulating chakra blurred the boundaries between natures considerably, allowing one to use ninjutsu of basically any nature.
But whether one could master the corresponding nature transformation was what mattered most. After all, this directly affected the power a ninjutsu could produce. Thus, although most jonin could use ninjutsu of other natures, they only specialized in the natures they excelled at.
For instance, the same wind release technique would be completely different when used by a ninja who had mastered nature transformation and one who had not.
Even after Kakashi later mastered five chakra natures, he ultimately chose only the lightning nature he excelled at most and the earth nature for defense. He mostly used the others as circumstances demanded, rather than treating them as regular methods.
At present, Hiruzen Sarutobi was the only person known to have mastered the nature transformations of all five chakra natures. His proudly self-created ninjutsu, the Five Release: Great Combo Technique, could be called a ninjutsu packed with stats, effort, and mechanics.
You could say Hiruzen Sarutobi fell short in all sorts of ways, but you could not say that about the Five Release Great Combo Technique. That thing's destructive power really was outrageous.
Before they knew it, half a year had passed.
In the courtyard, Kakashi and Yuzuru were sparring.
They began by pitting their swordsmanship against each other. Through daily training and stimulation from chakra, both possessed excellent speed, stamina, and strength.
But since both used Hatake Kenjutsu, their exchange produced no results beyond the repeated clacking of wooden swords colliding.
They had learned from the same teacher. Neither could break through the other's moves.
Then Kakashi suddenly formed hand seals in rapid succession. Genjutsu: Hell Viewing Technique!
He wanted to use genjutsu to make Yuzuru reveal an opening, but unfortunately, genjutsu of this level had no effect on Yuzuru.
He had already been secretly stimulating the nerves in his brain with Ice Release. The distinctive cool sensation allowed him to maintain absolute focus.
But just then, Yuzuru's body wavered slightly. Kakashi seized the opportunity and immediately slashed at him with his sword.
He felt a solid impact. His wooden sword had indeed struck something tangible, but unfortunately, it was not Yuzuru himself. It was a log.
The next second, Kakashi hurriedly used the Substitution Technique too. Just after he changed positions, Yuzuru appeared where he had been standing and slashed down with his sword.
Kakashi seized the opportunity to immediately cast Earth Release: Headhunter Jutsu.
Unfortunately, only after the Yuzuru before him had been buried underground with just his head exposed did Kakashi realize that this Yuzuru was actually the wooden dummy they normally used for sword practice.
"How? Oh no!"
The next second, a chill spread through his body. The flow of chakra inside him instantly slowed, and even he himself shuddered violently.
"You lost again~"
Hearing the voice beside his ear, a trace of regret flashed through Kakashi's eyes before they returned to their usual dead-fish look.