Taking advantage of the fact that Tsunade hadn't woken up yet, Yako hurriedly slipped out of her room, one hand pressed against his lower back.
He had to leave.
What if she woke up still in the mood? There was no way he could admit he couldn't keep up.
A man had to be flexible—when it was time to retreat, he retreated. Otherwise, he'd suffer.
Besides, Yako was busy.
Today, he was supposed to take Uzumaki Kushina out for special training.
—
At the Senju training grounds, he found Kushina resting while Namikaze Minato was training nearby.
Minato gripped his right wrist with his left hand, his entire body tensed as he focused on his palm.
There, an unstable sphere of chakra spun rapidly.
Rasengan…
Minato had once seen a Wood Golem seize a Tailed Beast Ball—and from that, he had begun developing the prototype of the Rasengan.
Yako thought to himself—enough of secrets, I'll put on a show in front of Minato.
"Kushina, let's go. I'm taking you out of the village for special training today."
Kushina's eyes lit up.
Fox was always busy—he had been gone for a full month on missions.
According to Tsunade, he had even killed the rogue ninja Uchiha Madara.
—
Three days later, late in the morning, Yako once again stepped out of Tsunade's room and arrived at the training grounds.
Minato was still working on the Rasengan.
Some things clicked instantly once explained—but without guidance, one could struggle for years.
Minato had already spent a long time on it, yet he still couldn't stabilize the rapidly rotating chakra sphere.
A figure appeared in a flash.
Blocking the sunlight, Yako stood before him.
Minato looked up.
"Fox-sama, are you here to take Kushina for training?"
He dispersed the chakra sphere in his palm.
Kushina quickly ran over.
Seeing Yako staring at his hand, Minato spoke hurriedly.
"Fox-sama, this is a half-finished jutsu I'm developing…"
Yako nodded.
"Gathering chakra into the palm, forming a high-density rotating sphere… it resembles a Tailed Beast Ball.
The overall direction is correct.
But the details are a mess."
Minato's heart raced.
Was Fox-sama about to guide him?
Yako raised his hand. Chakra gathered in his palm—and began to rotate.
"I noticed your chakra rotates in a single direction, around a vertical axis.
That means the destructive force is limited to one direction. The power is too weak, and the sphere can't contain much chakra.
But if you make the chakra flow in multiple directions, constantly shifting, constantly rotating—and compress it…
The power will increase significantly."
As he spoke, a perfectly formed Rasengan appeared in his hand.
Minato's eyes widened in shock.
Fox-sama had only glanced at his incomplete jutsu—yet not only pointed out the flaw, but instantly completed it?
The sphere in Yako's palm was flawless.
Chakra spun at high speed within it, even producing a faint buzzing sound.
Yako continued,
"For someone with immense chakra reserves, continuously feeding chakra into it means its power has no upper limit."
He raised his hand.
The Rasengan expanded instantly—its diameter growing to the height of a person.
Yako leapt into the air, flipping his body, and slammed it down.
The ground shattered.
Grass, soil, rock—everything was ground into fragments and blasted apart.
A massive crater, several meters deep, formed in the earth.
Yako nodded in satisfaction.
"Not bad. Decent enough. Suitable for those with massive chakra reserves."
Minato and Kushina approached the crater.
They stared at the exposed rock layers, their expressions stunned.
Even solid stone had been carved into a perfectly smooth concave surface.
Minato could hardly believe it.
Had his jutsu really possessed such potential?
Yako added,
"This is the pinnacle of shape transformation. It suits Kushina perfectly.
If you add nature transformation, it can be adapted for other shinobi as well."
Kushina hurriedly asked,
"Fox-sama, this jutsu suits me? How should I use it?"
"Like this."
Yako clapped his hands.
A wooden fox burst from the ground.
It raised its claw—and a Rasengan formed before it.
"Kushina, your chakra fox claws can extend freely, just like my Wood Release.
The short range of the Rasengan… isn't a problem for us."
The wooden fox's claw extended with crackling sounds, shooting forward and smashing into a tree.
The tree exploded into fragments.
After a moment of thought, Yako said,
"For now, focus on training the chakra sphere. Work with Minato to perfect it."
With that, he vanished.
—
Kushina grabbed Minato's arm excitedly.
"Minato! You were right! Just like you said—once completed, this jutsu suits me perfectly!"
Minato stared at the crater, then at the shattered tree.
"Fox-sama is the truly incredible one.
He only took one look… and perfected the jutsu…
People call me a genius—but I often feel unworthy of that title.
Fox-sama… the one who killed Uchiha Madara…
He's the real genius."
What they didn't know—
Was that Yako had secretly spent three full days training in private, following the original method, just to pull off that display.
—
Two months later, in a remote valley outside Konoha—
Behind Kushina, four translucent chakra tails floated.
Within each tail… was an Adamantine Sealing Chain.
She swung her hand forward.
A chakra fox claw shot out—
And at its tip, a Rasengan formed.
The claw drove the Rasengan forward at high speed, slamming into the mountainside.
Together, they carved out a massive crater.
Yako nodded repeatedly.
The Rasengan and a Jinchūriki… truly were a perfect match.
The Rasengan was a close-range technique—hard to land.
In the original approach, Naruto relied on Multiple Shadow Clones to increase accuracy, which consumed enormous chakra.
But Kushina was different.
Her sealing techniques far surpassed Naruto's.
Her control over the Nine-Tails' chakra at this age was far superior.
Her growth would be much smoother.
—
On a ridge above, Minato spoke.
"Fox-sama… maintaining the Nine-Tails' seal is very taxing for Kushina.
I've been studying sealing techniques as well, hoping to help her."
His tone was casual—almost as if it were a passing remark.
"Ordinary sealing techniques aren't very effective… Fox-sama, have you heard of the Reaper Death Seal?"
Yako immediately turned, locking his gaze onto Minato.
"The Reaper Death Seal… a technique tied to the Shinigami…"
"Shinigami…" he murmured.
"Is it dangerous?" Minato asked.
Yako spoke slowly.
"Chakra is made of physical energy and spiritual energy.
A human consists of body and soul.
The Reaper Death Seal… touches the soul itself.
A shinobi can only use it once in their lifetime.
Make a mistake… and you die completely."
He paused.
"The soul… that is the domain of gods.
Any technique that manipulates it… is a forbidden jutsu."
Then he looked at Minato.
"After we return to the village, come with me to see Tsunade.
I also need this Uzumaki clan forbidden technique.
We'll study it together."