Upon returning to camp, Yako began researching a chakra storage seal inspired by the Yin Seal.
The Uzumaki clan's Yin-Yang sealing system was built on the foundation of Yin Release and Yang Release chakra.
Yin and Yang gave rise to one another, entwined in mutual balance—only through that cycle could true stability be achieved.
Drawing out both Yin and Yang chakra, Yako shaped them into a swirling, dual-fish pattern.
Because of their inherent complementary nature, the chakra streams spun calmly around a central point, forming the most basic sealed space: the rudimentary form of the Dual Balance Sealing Style.
The spinning Yin and Yang chakra streams formed the boundary of the seal. The hollow center became its core.
This was the simplest version of the technique.
Yako tried injecting chakra into it.
The chakra didn't immediately dissipate—it clustered within the seal.
But the structure was too simple, the binding too weak. The chakra slowly began leaking away.
Especially in the vertical direction—above and below the seal—there was no containment. It compressed into a tiny core, like the seed of a jujube.
To fix that, Yako attempted to overlay another Dual Balance Seal perpendicular to the first—adding vertical containment.
Four streams of chakra bloomed in his palm.
At first, they clashed. Horizontal and vertical flows collided and destabilized, causing the seal to burst apart.
Yako tried again.
This time, he carefully adjusted the spacing between the seals, ensuring the chakra flows rotated without crashing into each other.
He injected more chakra.
The leakage slowed dramatically.
Now, the layered seals were stabilizing the internal chakra, bouncing it back inward rather than allowing it to escape.
But even then, the Dual Balance Seal was too weak.
Once the chakra inside exceeded a certain amount, the whole structure collapsed.
Not enough.
A new system was needed.
The Four Symbols Seal was a known upgrade to the Dual Balance Seal—far more stable.
Yako replaced the horizontal layer with "Greater Yang" and "Greater Yin," and the vertical with "Lesser Yang" and "Lesser Yin."
Greater Yang was composed of two Yang Release chakra streams.
Greater Yin was two Yin Release streams.
Lesser Yang fused one Yang and one Yin stream.
Lesser Yin was one Yin and one Yang, in reverse.
Altogether, the seal was built from eight chakra streams.
Those streams couldn't collide or destabilize. Their speed had to be just right—not too fast, not too slow.
The complexity skyrocketed.
Just constructing the seal took Yako fifteen full days.
But when he finished—it worked.
This new seal could store chakra stably. After testing it, Yako confirmed it could hold enough chakra to cast five full-power techniques.
In battle, that meant he could unleash five jutsu immediately, taking the initiative.
He named the technique: Ten Seal.
He hadn't expected to have such talent in sealing arts.
Without delay, he summoned Black Ape.
The older shinobi stepped into the captain's tent, confused by the sudden summons.
Yako said bluntly, "You're twenty-three. I've noticed your chakra hasn't increased in the last three months. In the last battle, you ran out completely."
Black Ape's expression darkened.
He'd realized it himself. No matter how long or how hard he trained each day, his chakra reserves stayed the same.
His taijutsu and ninjutsu had hit their limits too.
"No need to worry," Yako said. "I have an idea. If you work with me, we might be able to break through that ceiling."
"Really? I… still have a chance, Captain?"
"Of course you do. But first—let me check something. I need to know if you have the potential for Yang Release and Yin Release chakra."
Both were rare talents. Not everyone possessed them.
Yako ran a diagnostic.
Black Ape could sense the Yang Release chakra Yako funneled into the back of his hand… but not the Yin Release.
"Just Yang Release, then."
That was a pity. It meant Black Ape couldn't learn the Ten Seal on his own.
But Yako had a workaround.
He formed the necessary hand seals and completed the Ten Seal. Then he pressed his hand to Black Ape's.
A cross-shaped mark appeared on the back of Black Ape's hand, taking up nearly the whole space.
The center of the cross was hollow.
Each of the four arms represented one component of the seal: Greater Yang, Greater Yin, Lesser Yang, and Lesser Yin.
"This is my first field application," Yako said. "We'll improve it together from here. Now—try storing chakra."
Black Ape focused.
The chakra he gathered didn't return to his core—it vanished.
His hand burned. The seal had activated.
The cross began to spread and morph—slowly shifting into a diamond.
'So that's why Tsunade's Yin Seal looks like a diamond,' Yako mused. 'Her design must be more refined than mine.'
But what mattered was this seal was Yako's own—handcrafted, tailored to his needs.
He understood every step. Every principle.
Which meant he could continue improving it on his own.
"Let's go. We're heading to the training ground."
Once there, Yako said, "I'll teach you a hand seal sequence. It'll let you activate the seal."
Black Ape mimicked his movements, remembering how the chakra was meant to flow.
His hand burned again.
Stored chakra surged back into his body.
"Don't draw on your usual chakra pool," Yako instructed. "Use the stored chakra."
Black Ape nodded and formed seals.
"Earth Release: Earth Longspear!"
Four stone spears burst upward and stabbed at the central target from different angles, simulating a lethal strike pattern.
"I—what? That wasn't my chakra?"
His eyes widened.
"That… that was from the seal?!"
Black Ape was ecstatic. His chakra problem was solved.
With this seal, he didn't even need to extract chakra during battle. It was like carrying a preloaded scroll—faster and more reliable.
After three straight days of training, he could now deploy the stored chakra freely.
When the seal was fully charged, he could fire off five jutsu.
And if he concentrated the chakra into one blast… it could reach jonin-level scale.
"Captain!" he beamed. "I'm still a tokubetsu jōnin, but I've got a jonin-level jutsu in my back pocket now! That's huge!"
Yako nodded repeatedly, fully satisfied with the results.
"Black Ape—the Ten Seal's performance trial is complete. Now comes the stimulation test."
"Stimulation test? Stimulating what?"
Black Ape grew even more excited. Did the seal have hidden features?
Yako explained, "You'll fully charge the Ten Seal. Then, after your body and chakra have naturally recovered, you'll release the stored chakra into your system."
"I want to see how your body reacts to operating above its chakra ceiling. If there's any adaptive response… if you can grow stronger from the strain."
"This test is dangerous. We'll go slow. Add chakra bit by bit."
Black Ape's eyes were firm.
Just having a jonin-scale trump card already felt like a miracle.
But if this could push him even further?
It would change everything.