A jutsu like the Rasengan holds immense value for Tobirama Senju at this stage. In fact, its value would only increase once he eventually develops the Flying Thunder God Technique.
After all, the Rasengan was originally created to complement the godlike speed of the Flying Thunder God. So it's no surprise that someone like Tobirama, known for his speed, would be intrigued by the incomplete version in Yujin's hands.
So when would Tobirama consider the Rasengan to be "devalued"? The answer: only after he develops the Flying Thunder God Slash.
To continue developing the Rasengan, Yujin needed the aid of a Clone Technique. But where would he get one?
Tobirama hesitated for a moment, then eventually gave in—figuring he might as well go the extra mile. He'd already gifted three jutsu; what was a little more generosity?
"As for Clone Techniques, I could teach you... the Shadow—hmm, how about the Water Clone Technique?"
Thankfully, he wasn't the type to give away the farm. A B-rank Shadow Clone was unnecessary—C-rank Water Clone was practical enough.
Yujin didn't push his luck. As long as he could benefit from this exchange, he was content. So, he released the chakra in his hands and began practicing the Clone Technique.
Clone Techniques are extremely practical—perhaps even the most practical category of ninjutsu. In real combat, it's often true that 0.5 + 0.5 > 1.
It had to be said: splitting one's consciousness was a strange and fascinating experience.
Given Yujin's current strength—on paper, at least Special Jōnin level—learning a C-rank technique was no challenge. By the next day, he had already mastered the Water Clone Technique.
Tobirama continued to recover from his injuries and showed no signs of leaving just yet.
With the Water Clone Technique in hand, Yujin immediately began experimenting with "synthesizing" the Rasengan.
Being cautious and safety-conscious, Yujin and Tobirama headed to an area far from the camp to avoid any potential mishaps during training.
"Here we go."
Yujin glanced at Tobirama beside him. His words were both an announcement and a disclaimer—You're standing this close, so don't blame me if something goes wrong.
He cast the Water Clone Technique, distributing chakra into the clone. Then he extended his left hand to release chakra while suspending his right hand over the left palm to compress it.
Once the chakra sphere was sufficiently "solidified," the clone began to spin it clockwise with both hands. Taking inspiration from the Rasengan's original creator—Naruto—Yujin's own form was similarly unrefined. The clone's hands flailed around like cat paws, awkwardly pawing and pushing from left to right.
As the clone's hand speed increased, the chakra sphere—composed of tightly compressed chakra—began to spin. At first, the rotation was slow, but with the clone's efforts, the center of the sphere developed what felt like powerful gravitational pull, drawing the outer chakra into an increasingly rapid spin.
Then came a short, crisp sound—dense but tinged with lightness, like wind rushing through a hollow steel pipe.
Despite its seemingly weightless nature, the chakra, due to its extreme spin and potential explosive force, gave Yujin's palm a sense of weight.
"This might just work…"
The Rasengan's shape and power seemed to be taking form. But just as Yujin's face was about to show a smile, the smooth surface of the chakra sphere began to distort and tremble.
Seeing this, Yujin instinctively tightened his right hand's grip—but this only made the chakra sphere shudder violently. Then—
BANG!
The chakra sphere exploded like a popped balloon. The violent shockwave instantly dispersed the clone into a puddle, and Yujin himself was sent sprawling backward in a heap.
The nearby flowers and grass were caught in the crossfire.
And Tobirama? The moment the chakra sphere showed signs of instability, Tobirama had already retreated to a safe distance. Come on—after experiencing countless "lab accidents" as a ninjutsu developer, how could he possibly be caught off guard by such a basic mishap?
"Didn't handle the final stage properly," Yujin muttered, climbing to his feet, now covered in dirt.
But he wasn't discouraged—on the contrary, he felt hopeful. Encouraged by the near success, he immediately attempted a second trial—only to fail again.
After five consecutive failures, Yujin still hadn't made any progress.
That's when Tobirama, who had been silently watching the whole time, finally spoke. "Ahem. Mind if I give it a try?"
"Of course," Yujin replied, glad for the break. He was also curious whether Tobirama had any new insights.
Tobirama used the Clone Technique to create two duplicates. He had already figured out the trick.
If you divide the Rasengan into three components: the first is releasing large quantities of chakra, the second is high-speed chakra rotation—both of these can be done somewhat roughly. The real challenge lies in the third component: maintaining the shape.
Tobirama's original body cupped his hands and released chakra. One clone handled the shape control, and the other managed the rotation.
It only took him three attempts to reach the same level of progress Yujin had achieved.
Though the approach was essentially copied from Yujin, Tobirama's talent for jutsu development was undeniably impressive.
Another bang like a balloon bursting rang out. Tobirama instantly shunshinned away, while the clone was obliterated.
Yujin looked at Tobirama with a hint of grievance—those were Shadow Clones... B-rank jutsu really were better.
Tobirama didn't fear failure. In fact, his eyes were shining even brighter now.
The popping sounds of failed Rasengan attempts continued echoing in the distance.
Immersed in the process of ninjutsu development, Tobirama was far more focused than Yujin. The first day brought no progress. On the second day, they exchanged insights. By the third day, Tobirama stopped eating, drinking, and talking altogether.
On the morning of the fourth day, Yujin—dozing beneath a tree—once again heard that distinct sound, but merely rolled over without reacting.
Forming the high-speed spinning chakra sphere wasn't the issue anymore. The challenge was in sustaining it at the final stage. So Yujin had grown used to hearing the familiar pop.
But—
Something was off. There was no explosion.
His eyes flew open, and he leapt to his feet, turning toward Tobirama.
Tobirama had worked through the night. He looked a bit disheveled, but his face was radiant with energy. He and his two clones had finally managed to maintain the chakra sphere's shape. At this point, it could truly be called a Rasengan.
"You... you're kidding me... That talent of yours is just insane!" Yujin said, utterly astonished.
He wasn't comparing Tobirama to himself—but to Naruto, who, despite being the fastest learner and skipping steps, had still needed a full month to master the Rasengan. Tobirama? This was only day four.
"Talent?" Tobirama shook his head. "It's not talent. I just used the dumbest method."
Dumb method?
Yujin blinked, confused. Was Tobirama being sarcastic?