Mathematics

Tobirama Senju was, of course, not being sarcastic. He was simply stating the truth.

Although the clone he used while experimenting with the Rasengan had been one more than Yuzhen's, this was still only the development stage of the technique. Producing stable results was far more important than its practical combat properties.

Actual combat would be something to consider next.

The Tobirama Senju clone responsible for applying the "rotation" released its hands and stepped aside. The original and the other clone carefully held the Rasengan and brought it toward the trunk of a large tree.

The Rasengan's power went without saying. It embedded itself in the tree trunk without the slightest effort.

Tobirama Senju was extremely satisfied with this level of power. At this stage, the Rasengan could finally truly be called a Rasengan.

After dispersing the chakra in his hands, the three Tobirama Senjus gathered together again. Moments later, another Rasengan appeared in their hands...

This proved that his earlier success had not been a stroke of luck.

He had genuinely grasped the trick.

Tobirama Senju dispersed the Rasengan again. Seeing that Yuzhen seemed about to ask something, he spoke first. "I'll explain after I wake up. Right now, I need to rest for a while."

With that, he came to the spot where Yuzhen had been lying moments before and flopped down. In the blink of an eye, faint snores followed.

Tobirama Senju was indeed extremely exhausted.

Although he possessed extraordinary talent for developing ninjutsu and had managed to achieve results in such a short time, the effort and sweat he had poured into it could not be overlooked.

It was just that...

Yuzhen felt that this kid was quite good at keeping people in suspense.

Tobirama Senju slept for four or five hours. Only after he ate a little and replenished himself with plenty of water did he explain things to Yuzhen:

"Under normal circumstances, controlling the shape of the Rasengan requires grasping a certain kind of 'balance.'

"Most ninja have to rely on their own senses and maintain this balance through the experience gained from repeated attempts.

"And when it comes to finding that correct 'feeling,' it would not be unusual for an ordinary person to spend three to five years."

That was quite accurate. If Yuzhen remembered correctly, the Fourth Hokage had spent three years developing the Rasengan.

"I'm different. I used a stupid method and turned an abstract feeling into concrete numbers."

"Tell me more." Yuzhen naturally wanted to know how Tobirama Senju had done it.

"The chakra used for the Rasengan can be divided into two parts. One part is the chakra responsible for rotation, and the other is the chakra used to maintain its shape. So how much chakra should be used for rotation, and how much should be used to maintain the shape?"

"This question naturally has a specific answer. If we treat the amount of chakra rotating inside as 100, then first, the chakra has to be compressed into a spherical shape. The amount of external chakra required at that point must be greater than 100. That's easy to understand."

"When the chakra begins rotating at low speed, the amount of external chakra needed to maintain its shape is 57."

"When the chakra begins rotating at medium speed, the amount of external chakra is 35~~23."

"When the chakra rotates at top speed, the amount of external chakra drops to 15."

"I worked these figures out bit by bit. They have nothing to do with so-called talent. I really did use the stupidest method."

Yuzhen: "..."

He understood that Tobirama Senju was not talking about absolute numbers, but ratios. However... this method was indeed very, well, down-to-earth. Yet Yuzhen had never thought of it this way. Who would have expected data analysis to be used in the development of ninjutsu?

Not only had he failed to think of it, even the Fourth Hokage, who had invented this technique, surely had not thought of it either.

After thinking for a moment, Yuzhen could not help saying, "I didn't expect this to be such an effective verification method. But precisely controlling the amount of chakra output isn't simple for ordinary ninja either."

It was easy to say and hard to do. Even if someone told Yuzhen when to produce an amount of 57, could he do so with precision?

Tobirama Senju nodded. "That requires persistent practice. In fact, the figures can be made somewhat less precise and the Rasengan can still be formed. It's just that when developing a technique, one should always strive for perfection."

"As for figures like 57 and 15, they aren't precise either. Next, I plan to refine the internal and external chakra ratio of the Rasengan by another order of magnitude."

"..."

What else could Yuzhen say? All he could say was, "As expected of you."

Tobirama Senju continued using his "stupid method." After spending a week, he ultimately refined the figures by another order of magnitude, down to one or two decimal places. However, data that precise was already beyond what Yuzhen could pursue.

Yuzhen only wanted to use the Rasengan smoothly in actual combat. He did not insist on achieving the technique's maximum or optimal power.

According to Tobirama Senju, even if the Rasengan were made more refined, the resulting damage would at most increase from 100 to less than 110.

Yuzhen had a fair amount of self-awareness. When it came to chakra control, if there was something he could not do, then he simply could not do it.

Of course, Tobirama Senju had only found the optimal ratio for now. Even he could not yet apply the Rasengan in actual combat.

Leaving Yuzhen aside, Tobirama Senju's requirement for using the Rasengan was naturally to cast it instantly with one hand. Only then could it be combined with his Body Flicker Technique. He was still far from reaching that point.

Regardless, after completing the Rasengan's initial development, it was time for Tobirama Senju to leave.

The injuries on his body were no longer a problem. In fact, because of the Rasengan, he had already stayed here far too long.

When Tobirama Senju expressed his intention to leave, Yuzhen naturally had no reason to stop him. He had already gotten nearly all the benefits he could, and forcibly squeezing out more would be rather impolite.

"Let's stop here. I have a feeling we'll have another chance to meet in the future."

Yuzhen saw Tobirama Senju off. After they had left the camp behind by some distance, Tobirama said this.

They had only met by chance. Perhaps because he had gained something here while losing even more, Tobirama Senju had been left with a deep impression of these wandering ninja hidden in the mountains.

He was an extremely powerful sensory ninja and had already, consciously or unconsciously, memorized the characteristics of Yuzhen's chakra.

"Meet again? Perhaps. We wandering ninja could be wiped out at any moment. People as powerful as the Senju Clan, or your mortal enemies, the Uchiha, can't understand the feelings of weaklings like us," Yuzhen said.

Tobirama Senju opened his mouth, but in the end he could not hold back. "The Senju are indeed very powerful, but... have you ever heard the saying, 'Gale Swift Thunder, Swift Water Flowing Light'?"

Yuzhen froze for a moment. What did that mean? Could there actually be a clan in the ninja world stronger than the Senju Clan?

It was within Yuzhen's expectations that Tobirama Senju had completely ignored the Uchiha.

Tobirama Senju shook his head and did not explain further. He said, "The ninja world is so chaotic now that no one can say what the future holds. As I said... farewell for now. Perhaps we'll meet again by fate."

There was no need to drag things out. Tobirama Senju turned and left.

Yuzhen glanced at his departing back before returning to the camp.

Well, Tobirama Senju had left in impressive fashion—if one ignored the fact that the scroll on his back was filled with tea leaves.

Although Tobirama Senju had left, the benefits he brought did not end there.

After Yuzhen returned to the camp, he saw that where Tobirama Senju had been staying, a lone ninjutsu scroll had been placed on a simple wooden table.

A smile that said "just as expected" appeared on Yuzhen's face.

He went to the wooden table and opened the scroll. It recorded another Water Release ninjutsu, whose name was "Water Severing Wave."

This was, of course, not a return gift for the tea leaves, but a return gift for the Rasengan.

Although Tobirama Senju had helped overcome the Rasengan's greatest technical difficulty, the technique still had to be considered Yuzhen's ninjutsu. No matter how one put it, the principles and ideas behind it had all come from Yuzhen.

After all, the world of invention had an important principle: one percent was greater than ninety-nine percent.

Tobirama Senju had obtained the Rasengan, so he had to exchange it for an equivalently powerful offensive ninjutsu.

Yuzhen silently put away the scroll, thinking that Tobirama Senju had indeed lived up to his expectations. He was a man who knew how to conduct himself.

People said that the older version of Tobirama Senju was sinister, crafty, and unscrupulous. But after actually interacting with him, Yuzhen decided to abandon that stereotyped view. Tobirama Senju was clearly a kind man who repaid kindness and treated everyone fairly.

After finishing The Art of Communication, he decided to write another book titled The Art of Trading.