With Yamamoto's pride, there was no way he would entrust the protection of Soul Society to others so easily.
When Aizen entered Negación, Yamamoto agreed to Hirako's proposal for two reasons: first, to ensure the safety of the severely injured captains; second, to use that brief window of battle to gather intelligence on Aizen.
From the actions of Hirako's group and Urahara, Yamamoto deduced that Urahara Kisuke was someone who understood Aizen's abilities.
What he hadn't expected, however, was that not only Urahara—but even other captains—knew something about Kyōka Suigetsu. Worse still, his own two disciples had hidden the truth from him, claiming it was to prevent him from being manipulated into attacking fellow captains.
Yamamoto had harshly reprimanded the two overconfident students.
Then, he issued an order as Head Captain:
Unohana Retsu would use Bankai to heal both herself and Zaraki Kenpachi, and the three of them—Yamamoto and the two generations of Kenpachi—would confront Aizen together.
After activating Minazuki, Unohana would not excessively drain her Reiatsu by healing only two people, allowing her to retain most of her combat strength.
As for Kenpachi—
He was a weapon.
Even Yamamoto had to acknowledge the terrifying power of Kyōka Suigetsu, which controlled all five senses.
But that didn't mean it was unbeatable.
Yamamoto's Ryūjin Jakka granted him control over flames.
To a certain extent, this meant he could perceive temperature with extreme sensitivity—not through his own senses, but through his Zanpakutō as a medium.
As long as he monitored fluctuations in heat—
He could locate the enemy.
Whether it was truly Aizen or not didn't matter.
He would simply cut.
By this logic, Hitsugaya could theoretically do the same through ice—
But both he and Hyōrinmaru were still lacking.
So Yamamoto did not bring him.
Unohana's method was even simpler.
Killing intent.
After activating Minazuki, her own murderous aura clashed with that of her opponent, allowing her to pinpoint them with ease.
This was not one of the five senses—
But an instinct honed through mountains of corpses and seas of blood.
She could strike before the enemy even moved.
And finally—
Kenpachi.
Yamamoto himself had approved Unohana's transfer to Squad 4, so he knew exactly what kind of monster Kenpachi was—
A being born for battle.
Before Unohana healed him, Yamamoto crouched before Kenpachi and gave a single instruction:
"Do not trust anything you see or hear. Fight purely on instinct."
That was it.
Let go of everything—
And fight with the heart.
Combat instinct.
An abstract concept—
Yet not unlike Tsunayoshi's Hyper Intuition.
A natural ability possessed by monsters like Kenpachi.
Lines of Kidō Reiatsu carved through the sky—
Four edges forming a massive inverted pyramid that enclosed Sōkyoku Hill.
"Bakudō #73: Tozanshō!" ×4
The barrier was cast jointly by:
Urahara Kisuke, Shihōin Yoruichi, Shiba Kūkaku, and Hachigen Ushōda.
"Aizen," Yamamoto said, drawing his blade, "this barrier is not to trap you—"
"It is to trap myself."
This was an improvised plan.
Yamamoto had asked Urahara whether it was possible to temporarily seal off the battlefield.
With limited time, Urahara gathered the strongest Kidō users available.
Even Shiba Kūkaku, who had been dragged in after returning to help rescue Rukia.
Now—
With the barrier complete—
Yamamoto revealed his true intent.
"Bankai."
The interior of the barrier erupted into a sea of flames.
The temperature skyrocketed.
Yamamoto stood at the center—
His haori already reduced to ash.
Eyes closed.
Battle intent rising.
In his hand—
A blazing Zanpakutō.
"Sword of Infernal Flame."
Tsunayoshi's eyes flickered.
So it's not Zanka no Tachi…
He understood immediately—
Yamamoto was using his Zanpakutō as sight.
This environmental manipulation—
Was not the absolute destructive power of Zanka no Tachi—
But a battlefield of fire.
At the moment Yamamoto released Bankai—
Unohana and Kenpachi moved as well.
They sealed off their five senses with Reiatsu—
Relying only on their own methods.
Unohana chose Ichimaru Gin.
His extended blade intrigued her.
Perhaps—
He could bring her a bit more joy.
Kenpachi, meanwhile, looked at Tōsen Kaname with mild disappointment.
The weakest of the three.
Still—
A captain-level opponent was still worth fighting.
The battles began instantly.
Unohana didn't approach.
Instead, her blood blade extended into a whip, lashing toward Gin.
Gin responded without hesitation—
Kamishini no Yari.
The blade shot forward, tearing through the blood sea.
They clashed at long range—
Yet were the first to engage.
Kenpachi roared with excitement and charged.
Tōsen grimaced.
He was far from full strength—
But had no choice.
He donned his Hollow mask and fired clumsy Cero blasts, using Suzumushi: Benihikō to stall—
Before being dragged into close combat.
Meanwhile—
Aizen focused entirely on Yamamoto.
He had already realized—
These three had found ways to bypass Kyōka Suigetsu.
Yamamoto charged.
Using the "vision" from his flames—
He struck without hesitation.
"Flame Tornado."
A massive inferno engulfed Aizen.
But—
A mirror-like blade emerged.
"Mirror of Absolute Clarity."
With a single slash—
The flames were cut apart.
The surrounding sea of fire began to turn reflective—
Mirror-like.
Aizen had seen through Yamamoto's method.
If Yamamoto relied on heat—
Then he would erase the distinction.
Aizen merged himself with the mirrored environment—
Becoming one with the flames.
Yamamoto immediately sensed it.
The feedback from his blade vanished.
Only one conclusion—
Aizen had hidden himself.
Without hesitation—
Yamamoto drove his blade into the ground.
Flames surged wildly.
The fire solidified—
Turning into molten heat.
"Molten Inferno."
The temperature skyrocketed.
Outside the barrier, Urahara and the others were stunned.
At this rate—
The barrier's duration would be cut in half.
Inside—
Everyone stopped fighting.
Gin and Tōsen wrapped themselves in special insulating cloth.
Unohana submerged into her blood.
Kenpachi—
Endured it head-on with Reiatsu.
Even Tsunayoshi had to activate Sky Flames around himself—
To harmonize the environment.
No wonder Yamamoto was called a demon—
Without sufficient strength, one couldn't even stand beside him.
The technique worked.
The mirrored environment began to melt.
No matter what—
A mirror was still a mirror.
It could not withstand such heat.
Aizen was forced to reveal himself.
The moment he appeared—
Yamamoto moved.
The flames condensed instantly—
A single horizontal slash.
"Inferno: City-Burning Strike."
A near-white-hot blade of fire surged forward—
Pure destruction.
This strike—
Contained Yamamoto's entire understanding of flame.
It was this realization—
That led him, over a thousand years, to condense all fire into a single blade—
Creating the ultimate form:
Zanka no Tachi.
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