Upon returning to the main camp, Yagami immediately immersed himself in researching a chakra storage technique similar to the Strength of a Hundred.
The Uzumaki clan's Yin-Yang sealing system was built entirely on the foundation of Yin and Yang Release. Only when Yin and Yang gave birth to one another in a cyclical, interlocking loop could a stable state of equilibrium be achieved.
Yagami extracted Yin and Yang chakra, forcing them into a twin-fish vortex. Due to their unique mutually creative properties, the energies rotated steadily around a central axis, forming the most rudimentary sealing space. The rotating chakra served as the boundary wall, while the void in the center became the core of the seal.
This was the basic Two Pillars Seal.
Yagami attempted to inject standard chakra into it. It didn't dissipate instantly; instead, it gathered within the pocket. However, because the structure was singular and weak, the chakra slowly leaked out.
Specifically, in the vertical directions—up and down, perpendicular to the horizontal rotation—there was no constraint. The stored energy shrank away like a shriveling seed.
Seeing this, Yagami tried adding a second Two Pillars Seal, positioned vertically to intersect the horizontal one.
Four streams of chakra now swirled in his palm. At first, lacking proficiency, the horizontal and vertical streams collided, causing the seal to pop and vanish. He tried again, this time meticulously timing the rotations so the streams passed through each other's gaps without contact.
When he injected chakra this time, the dissipation rate slowed significantly. The energy was hemmed in by the two intersecting planes, bouncing back whenever it hit the boundaries.
Yet, the Two Pillars was still a "weak" grade seal. As he pushed more chakra into it, the internal pressure eventually overwhelmed the structural integrity, and the entire system collapsed.
'The structure is still too simple,' Yagami realized. 'I need the Four Symbols.'
The Four Symbols Seal was the reinforced version of the Two Pillars—vastly more stable. Yagami attempted to replace the horizontal Two Pillars with Great Yang and Great Yin, and the vertical one with Lesser Yang and Lesser Yin.
Great Yang consisted of two Yang streams; Great Yin of two Yin streams. Lesser Yang was one Yang and one Yin, while Lesser Yin was one Yin and one Yang. In total, the seal was now composed of eight distinct streams of chakra.
These eight streams had to rotate without annihilating each other, their speeds perfectly synchronized. The complexity of the geometry skyrocketed. It took Yagami fifteen days of constant trial and error just to construct the framework.
Fifteen days later, he finally stabilized the new seal.
It could store chakra with remarkable efficiency. In his current prototype, the seal could hold enough energy to release five full-scale ninjutsu. This meant he could enter a battle and immediately unleash five massive techniques to seize the initiative without dipping into his primary reserves.
Yagami named this technique the Cross Seal.
'Maybe my talent for sealing is better than I thought,' he mused.
He immediately called for Gorilla.
The man entered the Captain's tent with a look of confusion, unsure why he had been summoned.
"Gorilla, you're twenty-three now," Yagami began. "I've noticed your chakra levels haven't grown in three months. In our last battle, you hit your limit and ran dry."
Gorilla's expression darkened. He had realized three months ago that no matter how many hours he trained, his pool remained stagnant. Consequently, his Taijutsu and Ninjutsu had plateaued.
"Don't lose heart," Yagami said. "I have a theory. I want you to work with me to test something; it might solve your limit issue."
"Really? Captain... is there still hope for me?"
"There's always hope. Come here, let me check your affinity for Yin and Yang."
Yin and Yang affinities were rare; not everyone possessed them naturally. Yagami tested him and found that while Gorilla could feel the Yang chakra Yagami funneled into the back of his hand, he was completely numb to Yin Release.
"You only have a Yang affinity..."
It was a pity; Gorilla wouldn't be able to form the Cross Seal on his own. However, Yagami had a workaround. He performed the hand signs, completed the Cross Seal, and pressed his palm against the back of Gorilla's hand.
A cross-shaped curse mark appeared, filling the back of Gorilla's hand. The center where the lines intersected was empty, while the four branches of the cross represented the Great and Lesser Yin-Yang components.
"This is my first time trying this on someone else, so I don't know the exact results yet. We'll refine it together. Gorilla, try injecting chakra into the mark."
Gorilla focused, gathering his chakra at his hand. His energy vanished! He felt his hand growing hot as the seal activated. The lines of the cross began to expand slightly, slowly shifting toward a diamond shape.
'So that's why Tsunade's Yin Seal is a diamond,' Yagami thought. 'Her structure is likely more mature than mine.'
But Yagami preferred his own creation; he understood every rotation and principle behind it, allowing him to explore its potential further.
"Come, to the training grounds!"
Once there, Yagami taught him a specific seal to trigger the release. Gorilla mimicked the signs, following the chakra pathways Yagami described. His hand flared with heat again! The stored chakra flooded from the seal back into his system.
"Don't mold new chakra," Yagami commanded. "Try to use what just came out."
Gorilla complied, forming signs for Earth Style: Earth Flow Spear. Four jagged stone spears erupted from the ground, converging on a central point with lethal precision.
"I... I didn't mold any chakra! I used the energy from the seal!" Gorilla was ecstatic. His primary weakness had been solved. Having this seal was like carrying pre-loaded ninjutsu scrolls, only faster and more seamless.
After three days of intensive training, Gorilla mastered the draw. He could now fire off five extra techniques. Even better, if he concentrated the stored energy into a single burst, he could launch one Jonin-level technique—a massive jump from his Special Jonin baseline.
"Captain! I'm a Special Jonin, but I basically have a Jonin-level trump card now! This is incredible!"
Yagami nodded, satisfied with the results. "Gorilla, the power test for the Cross Seal is over. Now comes the 'Stimulation Experiment'."
"Stimulation? What am I stimulating?"
"Fill the Cross Seal to capacity," Yagami explained. "Then, wait until your natural body and chakra have fully recovered. After that, release all the seal's chakra at once. I want to see if forcing your body to hold chakra beyond its normal capacity will trigger a physical change—if the stimulation can force your ceiling to rise. This is dangerous. We will proceed slowly, increasing the stimulation bit by bit."
Gorilla's gaze turned resolute. Having a Jonin-level trump card was already a gift. If he could actually use this to push his inherent strength to a new height, it would be a life-altering transformation.
...
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