Tobirama Senju wasn't being sarcastic—he was simply stating the truth.
Even though he had used one more shadow clone than Yujin while testing the Rasengan, this was still the developmental stage of the jutsu. At this point, the key was stabilizing the result, not its combat effectiveness.
Combat was something to worry about later.
The clone responsible for applying the "rotation" effect stepped back, while the original Tobirama and another clone carefully held the Rasengan and brought it close to the trunk of a large tree.
The Rasengan's power was self-evident—it embedded itself into the tree trunk effortlessly.
Tobirama was very pleased with this level of power. At this stage, the Rasengan could finally be called a true Rasengan.
After dispersing the chakra in his hands, the three Tobiramas gathered together once again. Moments later, another Rasengan formed in their palms…
Which proved his earlier success wasn't just dumb luck.
He had genuinely grasped the underlying principles.
Tobirama dispersed the Rasengan again, and seeing that Yujin seemed about to ask a question, he preemptively said, "I'll explain after I wake up. Right now, I absolutely need some rest."
With that, he slumped down onto the spot Yujin had just vacated. Within the blink of an eye, soft snoring could be heard.
Tobirama was indeed exhausted.
Though his talent in developing jutsu was extraordinary, the progress he had made in such a short time came from considerable effort and hard work.
Still…
Yujin thought this kid really knew how to keep people in suspense.
...
Tobirama slept for four or five hours. After eating something and rehydrating, he finally explained things to Yujin:
"Normally, to control the Rasengan's shape, you have to find a certain kind of balance.
Most shinobi rely on their senses and trial-and-error experience to maintain this balance.
And the process of finding the right feeling can easily take an average person three to five years."
That was pretty accurate. If Yujin remembered correctly, the Fourth Hokage had taken three years to develop the Rasengan.
"I'm different. I used a stupid method—turning abstract sensations into concrete numbers."
"Go on," Yujin said, naturally curious about Tobirama's approach.
"When using chakra for the Rasengan, it can be divided into two parts: one part is rotational 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 stability?"
"There's a specific answer to that. If we set the internal rotational chakra to a base of 100, then to compress it into a spherical shape, the external chakra needed must logically be more than 100. That's easy to understand."
"When the chakra is rotating at low speed, the external chakra needed to maintain the shape is 57."
"When it rotates at medium speed, the required external chakra drops to around 35–23."
"When it reaches high-speed rotation, it goes down to 15."
"I figured all this out little by little. It has nothing to do with talent—just the most basic, stupid trial-and-error method."
Yujin: "…"
He could understand that Tobirama wasn't referring to fixed numbers, but to proportions. Still… this method was certainly, well, pragmatic. Yujin had never thought of it this way. Who would've expected jutsu development to involve data modeling?
Not just him—the Fourth Hokage who invented the Rasengan probably hadn't thought of it either.
After some thought, Yujin couldn't help but say, "I didn't expect such a practical verification method. But even so, precise chakra control isn't something the average ninja can do."
Easier said than done. Even if someone told Yujin to supply a chakra output of 57 at a given point, could he actually do it with precision?
Tobirama nodded. "That's why it takes constant training. In fact, even with some leeway, you can still form a Rasengan. But when developing a jutsu, you should always aim for perfection."
"The values—57, 15—aren't exact. Next, I plan to refine the Rasengan's chakra ratio to an even more precise level."
"..."
What else could Yujin say? All he could do was sigh, "As expected of you."
Tobirama continued using his "stupid method," and over the course of a week, he refined the ratios again—down to decimal precision. But at that level, Yujin could no longer keep up.
All Yujin wanted was to be able to use the Rasengan reliably in actual combat. He didn't care about achieving the maximum or optimal power.
According to Tobirama, even the most refined Rasengan only increased destructive power from 100 to maybe just under 110.
Yujin had a good sense of his own limits. When it came to chakra control, if he couldn't do it, he couldn't do it.
Of course, even Tobirama hadn't reached the stage where he could use the Rasengan in battle.
He required the ability to "instantly cast it with one hand" to pair it with his Body Flicker Technique—and he was still far from that.
In any case, now that the Rasengan had reached its initial development milestone, it was time for Tobirama to leave.
His injuries had already healed. In fact, he had stayed here far too long because of the Rasengan.
When Tobirama told Yujin he intended to leave, Yujin had no reason to stop him. He had already gotten plenty out of their exchange. Pushing further would've just been rude.
"That's it for now. I have a feeling we'll meet again someday."
Yujin saw Tobirama off. After they had walked some distance from the camp, Tobirama turned and spoke.
Though their encounter had been fleeting, Tobirama felt he had both gained and lost something here. These rogue ninja hiding deep in the mountains had left quite an impression on him.
As a highly skilled sensory ninja, he had long since memorized Yujin's chakra signature—whether consciously or not.
"Meet again? Maybe. For us wandering ninja, annihilation can come at any moment. The powerful—like the Senju or your sworn enemies, the Uchiha—can never understand what it feels like to live as one of the weak," Yujin said.
Tobirama opened his mouth but then couldn't help replying, "The Senju are indeed strong. But… have you heard this phrase: 'Swift as the wind, sudden as lightning, flowing like water, radiant as light'?"
Yujin blinked in confusion. What did that mean? Was there a ninja clan even stronger than the Senju?
Tobirama's smooth dismissal of the Uchiha's strength didn't surprise Yujin in the least.
Tobirama shook his head and gave no further explanation. "The ninja world is in chaos right now. No one can predict the future. Like I said—farewell. Until we meet again."
There was no need for drawn-out goodbyes. Tobirama turned and left.
Yujin watched his departing figure, then returned to the camp.
Yes, Tobirama had left in style—if you ignored the scroll strapped to his back stuffed full of tea leaves.
...
Though Tobirama had left, the benefits of his stay lingered.
When Yujin returned to camp, he saw that in the place Tobirama had stayed, a lone scroll had been left atop a simple wooden table.
A knowing smile spread across Yujin's face.
He walked over, unrolled the scroll, and found that it contained another Water Release jutsu—Water Severing Wave.
This wasn't a gift in return for the tea leaves—it was a gift in return for the Rasengan.
Although Tobirama had helped solve the Rasengan's biggest technical hurdle, the jutsu still rightfully belonged to Yujin. After all, the original concept and theory had come from him.
After all, there's a saying in the world of invention: 1% inspiration is greater than 99% perspiration.
Since Tobirama had received the Rasengan, it was only fair to trade an equally powerful offensive jutsu in return.
Yujin quietly stowed the scroll away, thinking, Tobirama didn't let me down—he's a man of principle.
People often said that Tobirama was a cunning, ruthless man who'd do anything to achieve his goals. But having met him in person, Yujin decided to abandon that stereotype. Tobirama was clearly a righteous, fair-dealing, and honorable man.
Once he finished writing The Art of Communication, Yujin decided he'd write another book—The Art of the Deal.