Time rewinds to the moment the battle began.
Hueco Mundo.
Las Noches.
"It seems we have an uninvited guest arriving in Hueco Mundo."
Aizen sat on his throne, his right hand clenched into a fist, propping up his chin.
Unlike the composed Aizen, Kaname appeared somewhat shocked.
"Aizen-sama, is that Yamamoto's Reiatsu?"
"And it seems he is alone."
"That's right."
Aizen stood up. "I'll go see what our Captain-Commander is doing, coming to Hueco Mundo alone. None of you need to follow. There might be a major battle."
...
After Yamamoto was sucked into the spatial rift, in the blink of an eye, he found himself in Hueco Mundo.
A desolate white desert, and the white palace visible in the distance.
Just then, Aizen, wearing a high-collared, chest-baring white robe, his long hair flowing, walked over unhurriedly.
Yamamoto's eyes narrowed. "Aizen."
At the same time, he was astonished to find that he couldn't see through Aizen now. He couldn't sense any Reiatsu coming from him.
Aizen smiled slightly. "Captain-Commander, long time no see. To what do we owe the pleasure of your visit to Hueco Mundo?"
"Aizen, judging by your tone, have you crowned yourself the ruler of Hueco Mundo?" Yamamoto did not answer Aizen's question, asking one of his own instead.
"Heh heh, the ruler of Hueco Mundo? You could certainly think of me that way."
"Captain-Commander Yamamoto, let's fight."
As he spoke, Aizen glanced at the Zanpakutō in Yamamoto's hand. "Surely you didn't come to Hueco Mundo for sightseeing?"
Yamamoto scanned the surroundings. "This time, you don't plan on using cheap tricks to seal away my Zanpakutō?"
Aizen shook his head. "Using something like that once is enough."
The reason he created Wonderweiss before was that, prior to his complete fusion with the Hōgyoku, he wasn't confident in handling Yamamoto's Bankai.
The situation is different now. He will defeat Yamamoto head-on here and present a great gift to Shin.
"Where is your Zanpakutō?"
Only then did Yamamoto realize that Aizen was not carrying a Zanpakutō.
"I no longer need a sword."
"Arrogance!"
Yamamoto assumed Aizen meant he didn't need a sword to fight him.
"All things in the universe, turn to ash. Ryūjin Jakka!"
A tornado of flames enveloped Aizen.
Aizen didn't move at all, he simply narrowed his eyes, and the scorching flame tornado dissipated.
That last attack was merely a test.
At that moment, Yamamoto felt Aizen's Reiatsu, which was so potent it felt tangible. It was that very pressure that directly overpowered his flames.
"Unleash your Bankai. Speaking of which, I have yet to witness the Captain-Commander's Bankai."
Aizen clearly wasn't interested in the previous level of attack.
"Captain-Commander Yamamoto, if you were the man you were a thousand years ago, you would have attacked me without hesitation."
"Why have you regressed now? Such caution—have you truly grown old?"
Yamamoto said, "As you wish, arrogant boy. You shall be buried in my purgatory of fire."
The moment he finished speaking, a terrifying sense of dread erupted from Yamamoto, causing the nearby Hollows to scatter and flee.
"Bankai: Zanka no Tachi!"
His haori fluttered wildly in the blast of Reiryoku, and his shihakushō became tattered, revealing his toned muscles and the scars covering his entire body.
His Zanpakutō was no longer covered in flames but encased in charcoal, emitting a wisp of smoke.
"I see. All the flames have been sealed within the Zanpakutō."
Aizen realized this as he looked at Yamamoto's Bankai form.
Yamamoto instantly appeared before Aizen and slashed down, but Aizen dodged by shifting his body sideways.
Boom!
A massive fissure was carved into the white sand desert.
"The blade itself?"
"That's right."
Missing the first strike, Yamamoto followed up with a horizontal slash.
A glass-like, transparent shield of Reiatsu appeared in front of Aizen. Zanka no Tachi was blocked, unable to advance even an inch.
Aizen calmly said, "How regrettable, Captain-Commander. Your sword seems unable to shatter my shield."
"Ignorant boy!"
"Zanka no Tachi, East: Kokujitsujin!"
Yamamoto roared, leaped into the air, and brought his sword down toward Aizen.
The Reiatsu shield was shattered in less than half a second, and the blade rushed straight toward Aizen.
Aizen's eyes narrowed, and his body instantly vanished from the spot, transforming into a flash of light.
Yamamoto spoke in a calm tone, "The entirety of the flames' heat is concentrated at the tip of the blade. It neither burns nor releases explosive fire, but anything it touches vanishes without a trace."
"Aizen, no matter how strong your Reiatsu is, there is no chance of survival against my blade."
Aizen was unimpressed. "Oh? I will personally shatter that arrogance of yours."
Using his hand as a blade, he swung it, unleashing a massive slash.
"Zanka no Tachi, West: Zanjutsu Gokui!"
Endless flames erupted around Yamamoto, and immediately afterward, both his body and his blade were covered in intense fire. The slash vanished before it even touched his body.
"It's useless. You cannot even touch me."
"The temperature of Zanjutsu Gokui is 15 million degrees. You can imagine that my body and blade are wrapped in the sun itself."
Yamamoto walked toward Aizen step by step, the sand beneath his feet constantly melting. In moments, the sand separating the upper reaches of Hueco Mundo and the Forest of Menos where they stood had been reduced to nothing.
Under such extreme heat, the temperature of the entire Hueco Mundo rose significantly.
—
Inside Las Noches.
Kaname and the others who remained behind could clearly feel the oppressive Reiatsu emanating from Yamamoto.
Kaname lamented, "No wonder Yamamoto never used his Bankai in Soul Society. A Bankai like this would be a disaster for the entire Soul Society."
...
"Aizen, this ends now!"
"If I don't finish this quickly, I fear both you and Hueco Mundo will be burned to ashes along with me."
The moment he finished speaking, Yamamoto, his body wreathed in intense flames, charged at Aizen.
Hadō #90: Kurohitsugi!
A black coffin dozens of meters high completely enveloped Yamamoto.
The terrifying torrent of gravity on the surface of the black coffin alone was enough to inspire dread. But as the Kurohitsugi vanished, Yamamoto's body still stood firm in the same spot.
"It's useless, Aizen! If this is all you have, then you should not have come to challenge me!"
Yamamoto's expression was obscured by the flames.
Aizen smiled slightly. "Challenge? Is that what the Captain-Commander thinks? It seems you still haven't understood."
"Then let me reiterate. I will crush you, the so-called strongest Shinigami in a thousand years, from a position that transcends Shinigami, and let Soul Society listen closely to your final curtain call."
"Arrogance!"