"As expected of Kakashi Hatake, he held back far too much when facing Zabuza," Sora thought quietly.
He had now gained a clear understanding of Kakashi's strength and also realized how much he himself had grown.
This mission involving Zabuza had given him something far more valuable than victory.
Experience.
Fighting veteran Jonin like Kakashi Hatake and Zabuza had allowed Sora to clearly measure his own strength.
Not only that, but the strange mutation during his earlier training had nearly placed him in mortal danger, yet he had managed to turn that crisis into an opportunity.
As a result, his overall strength had improved greatly during this period away from home.
"My mother was right," Sora thought.
"At my current stage, simple training alone cannot bring decisive improvement. Only real combat can sharpen my abilities."
Especially battles against different types of powerful opponents.
The fights against Kakashi and Zabuza had greatly enriched Sora's combat experience.
His techniques were already sufficient to fight a Jonin like Zabuza.
However they were clearly not enough against someone like Kakashi, who possessed the Sharingan and powerful secret techniques.
"It seems it's time to take the next step," Sora murmured.
After leaving Kakashi and the others, Sora arrived at a quiet lakeside.
A Rasengan slowly formed in his palm.
This time he did not immediately use it to attack.
Instead he maintained the spinning sphere steadily.
A scorching airflow spread outward from his hand.
The surrounding air began to dry and heat up.
Sora was attempting something new.
He was trying to fuse Fire Nature Transformation chakra into the Rasengan.
He had already mastered nature transformation long ago.
However his chakra reserves had previously been too weak to integrate it into combat techniques.
But after his recent battles he realized that he was now ready to attempt this step.
His physique and spiritual strength were no longer what they once were.
His chakra reserves had already surpassed those of many Chunin.
It was now possible for him to perform S-rank level techniques, although he could not use them freely yet.
Such techniques still had to remain trump cards.
Only when he reached the Jonin level would he be able to use them casually.
For many years Sora had practiced Water and Fire Nature Transformations.
During his earlier training he had already learned how to burn leaves using Fire chakra.
Over the past two years he had also used both Fire and Water chakra to temper his body repeatedly.
Because of this his body had become extremely familiar with both elemental chakras.
There was almost no resistance when he used them.
This made the entire process much smoother.
Learning ninjutsu generally depends on three important factors.
The first is learning ability, often called talent or comprehension.
The second is chakra control.
The third is spiritual strength.
These three aspects determine how quickly a ninja can master new techniques.
Sora possessed all of these advantages.
He had long mastered both Water and Fire Nature Transformations.
His chakra control was extremely refined due to Tsunade's strict training since childhood.
His spiritual strength was also powerful because of the repeated Water and Fire Body Tempering.
The fact that he could sense Kakashi's genjutsu instantly during their fight proved this.
Because Sora had already mastered nature transformation for many years, integrating it into Rasengan was not starting from zero.
He was already halfway there.
With his extraordinary chakra control, the final fusion process progressed very quickly.
Streams of Fire Nature chakra continued flowing into the Rasengan.
The spinning sphere slowly began to change color.
The blue chakra gradually turned crimson.
Finally the Rasengan transformed into a blazing sphere of deep red flames.
It looked like a miniature sun resting in Sora's palm.
"Just a little more," Sora murmured.
Even with his experience and control, completing the technique in a single attempt was still difficult.
The technique was now about seventy to eighty percent complete.
The power of the Rasengan had already risen beyond an advanced technique and was approaching the level of an S-rank secret technique.
"I need to finish this before Zabuza arrives," Sora thought calmly.
"That way I will have more confidence in the coming battle."
Even Naruto had managed to integrate Wind Nature chakra into a technique in a short period of time.
Sora had already mastered nature transformation years ago.
His chakra control and spiritual strength were far superior.
The only disadvantage he had was lacking Naruto's massive number of Shadow Clones.
Still, Sora was confident he could complete the technique.
Determination flashed in his eyes.
He drank a bottle of Nutrient Solution.
Without Tsunade nearby he had to rely on this instead.
Compared to ordinary Soldier Pills, this nutrient solution was far more effective.
The powerful nutrition quickly replenished his body.
Sora began training intensely.
One Shadow Clone appeared.
Then another.
Soon twenty Shadow Clones surrounded him.
With his current physique and spiritual strength he could safely maintain this number.
However he intentionally avoided creating more.
Zabuza might appear at any moment.
He needed to remain cautious.
Twenty clones were more than enough.
After all the technique was already close to completion.
Meanwhile in the forest, Naruto stared at Kakashi with curiosity.
"Kakashi-sensei, what was that technique you used earlier, it looked incredibly cool and even defeated that flashy guy's ninjutsu," Naruto asked eagerly.
Sasuke also stared intently.
If Kakashi could teach him such a powerful technique, it would greatly increase his strength.
"You are mistaken Naruto," Kakashi said calmly.
"I did not defeat Sora's technique."
Naruto blinked in confusion.
"Kakashi-sensei, you are being too modest," Naruto replied.
"You say that because you don't understand the technique he used," Kakashi explained patiently.
"The technique in Sora's hand is called Rasengan. It was created by my teacher, the Fourth Hokage."
Everyone froze.
"What, the Fourth Hokage's technique?" Naruto shouted in shock.
Even Sasuke looked stunned.
The Fourth Hokage's reputation in Konoha was legendary.
He was one of the most powerful Hokage in history.
Techniques created by such a person were treasures countless ninjas desired.
Naruto looked extremely envious.
Sasuke's expression darkened slightly.
Unlike Naruto's simple admiration, Sasuke felt a surge of jealousy.
"That is correct," Kakashi continued calmly.
"Rasengan is a powerful ninjutsu created by the Fourth Hokage. However it is actually incomplete. If it were fully completed it would reach the level of an S-rank secret technique.
That is why I said I did not truly defeat the Rasengan."
Kakashi let out a quiet sigh.
That child named Sora possessed far too many unknown abilities.
...
Author's Note:
Naruto: Reborn as Tsunade's Son — Part 1 is now fully completed, with more than 130 chapters available on my Patreon!
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1.Dragon Ball: Oolong's Sex Adventure
2. Elements of Lust – ATLA & Korra Mixed Smut
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4. The Naive Me Who Became Someone's Everyday Secret
5. High School DxD: Rias Gremory, the Phenex Bride
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