Mathematics

Tobirama Senju wasn't being sarcastic, he was just stating facts.

Even though he used one more clone than Yuzhen when experimenting with the Rasengan, this was still the development phase of the jutsu. Stabilizing the results was far more important than practical combat application at this stage.

Combat application was something to consider next.

The clone responsible for applying the "rotation" released its hands and stepped aside. The main body and another clone carefully held the Rasengan, bringing it close to the trunk of a large tree.

The power of the Rasengan was self-evident; it embedded itself into the tree trunk effortlessly.

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

After dispersing the chakra in his hands, the three Tobirama Senjus gathered together again. In a moment, another Rasengan appeared in their hands…

This proved that his recent success wasn't just a fluke.

He had genuinely grasped the essence of it.

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

After saying that, he went to where Yuzhen had been lying, slumped down, and within the blink of an eye, light snoring could be heard.

Tobirama Senju was indeed extremely tired.

Despite his extraordinary talent in developing ninjutsu, the effort and sweat he put in to achieve results in such a short time could not be overlooked.

It's just that...

Yuzhen felt that this kid was quite good at teasing people.

Tobirama Senju slept for four to five hours. After he ate something and replenished his fluids, he began to explain to Yuzhen:

"Under normal circumstances, to control the shape of the Rasengan, one needs to grasp a certain specific 'balance.'

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

The process of finding this correct 'feeling' could easily take an average person three to five years."

What he said was quite accurate. If Yuzhen remembered correctly, the Fourth Hokage took three years to develop the Rasengan.

"I'm different. I used a crude method, turning an abstract feeling into concrete numbers."

"Can you elaborate?" Yuzhen naturally wanted to know how Tobirama Senju did it.

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

"There is certainly a specific answer to this question. If we consider the internal rotating chakra amount as 100, then first, to compress the chakra into a sphere, the external chakra amount required will inevitably be greater than 100. This is easy to understand."

"When the chakra begins to rotate at low speed, the external chakra amount to maintain the shape is 57."

"When the chakra rotates at medium speed, the external chakra amount is 35 to 23."

"When the chakra rotates at extremely high speed, the external chakra amount drops to 15."

"I figured this out bit by bit. It has nothing to do with so-called talent; it's truly the most crude method."

Yuzhen: "..."

He could understand that Tobirama Senju wasn't referring to specific numbers, but rather ratios. However... this method was indeed very, well, straightforward, but Yuzhen had never thought of it that way. Who would have thought that data analysis would be used in the process of developing ninjutsu?

Not only did he not think of it, but the Fourth Hokage, who invented this jutsu, certainly didn't either.

After thinking for a moment, Yuzhen couldn't help but say, "I didn't expect it to be such an effective verification method. However, precisely controlling chakra output isn't easy for most ninja."

It sounds simple, but it's difficult to execute. Even if Yuzhen were told when to output 57, could he do it precisely?

Tobirama Senju nodded, "This requires persistent practice. In fact, you can make a Rasengan with slightly more ambiguous amounts, but when developing ninjutsu, one always strives for perfection."

"57, 15, these numbers aren't exact 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? He could only say, "As expected of you."

Tobirama Senju continued to use his "crude method," spending a week to refine the data by another order of magnitude, meaning it was precise to two decimal places. However, such precise data was beyond what Yuzhen could pursue.

Yuzhen only hoped to use the Rasengan smoothly in combat and wasn't demanding its maximum or optimal power.

According to Tobirama Senju, even if the Rasengan was made more exquisite, the resulting damage effect would only increase from 100 to less than 110.

Yuzhen was self-aware; if he couldn't do something regarding chakra control, he couldn't do it.

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

Setting aside Yuzhen, Tobirama Senju's requirement for using the Rasengan was naturally "instantaneous activation with one hand." Only then could it be combined with his Body Flicker Technique. They were still far from that.

Regardless, after completing the preliminary development of the Rasengan, it was time for Tobirama Senju to leave.

His injuries were no longer an issue. In fact, because of the Rasengan, he had already stayed here for too long.

When Tobirama Senju expressed his intention to leave to Yuzhen, Yuzhen naturally had no reason to dissuade him. He had already gained as much as he could, and forcing more would be impolite.

"Let's leave it at that. I have a feeling we'll have the chance to meet again."

Yuzhen bid farewell to Tobirama Senju. After they had traveled a certain distance from the camp, Tobirama said this.

The two had only met by chance. Perhaps because he had gained something here and lost even more, Tobirama Senju had a deep impression of these rogue ninja hiding in the mountains.

He was a very strong sensory ninja, and had already unintentionally memorized Yuzhen's chakra signature.

"Meet again? Perhaps. For wandering ninja like us, annihilation is always just around the corner. Even strong clans like the Senju or your sworn enemies, the Uchiha, can't understand the feelings of weaklings like us," Yuzhen said.

Tobirama Senju opened his mouth, but in the end, couldn't help but say, "The Senju are indeed strong, but... have you ever heard the saying, 'Swift as the wind, fast as lightning, flowing like water'?"

Yuzhen was stunned for a moment. What did he mean? Were there even stronger ninja clans in the Ninja World than the Senju?

Tobirama Senju directly ignoring the Uchiha was within Yuzhen's expectations.

Tobirama Senju shook his head and offered no further explanation. He said, "The Ninja World is so chaotic now, who knows what the future holds. As I said... I bid you farewell, and may we meet again if fate allows."

There was no need for further pleasantries. Tobirama Senju turned and left.

Yuzhen glanced at the retreating figure before returning to his camp.

Well, Tobirama Senju had left with a flourish, if one ignored the fact that the scrolls on his back were filled with tea.

Although Tobirama Senju had left, the benefits he brought were more than just that.

When Yuzhen returned to the camp, he saw that where Tobirama Senju had been staying, a simple wooden table now held a single ninjutsu scroll.

A knowing smile spread across Yuzhen's face.

He walked over to the wooden table and opened the scroll. It recorded another Water Style ninjutsu called "Water Severing Wave."

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

Even though Tobirama Senju had helped overcome the greatest technical hurdle of the Rasengan, the jutsu still belonged to Yuzhen. After all, the principle and idea behind the jutsu came from Yuzhen.

After all, there was an important argument in the world of invention: 1% > 99%.

Since Tobirama Senju had obtained the Rasengan, he had to exchange it for a heavyweight offensive ninjutsu of equivalent value.

Yuzhen silently put away the scroll, thinking that Tobirama Senju had indeed lived up to his expectations; he was a man of principle.

People said Tobirama Senju was a sinister, cunning, and unscrupulous person, but after actually interacting with him, Yuzhen decided to discard such a rigid perception. Tobirama Senju was clearly a good person who repaid kindness and was honest with everyone.

After finishing 'The Art of Communication', he decided to write another book, 'The Art of Transaction'.