Aizen's high-speed regeneration and near-limitless spiritual pressure, fueled by the Hōgyoku, rendered most attacks useless.
Even if Shunsui Kyōraku used his Bankai to transfer his own injuries onto Aizen, they would instantly heal. And Kyōraku's strongest attacks, even in his Bankai state, were ineffective against Aizen's overwhelming spiritual pressure. Kyōraku's abilities were completely countered by Aizen.
As Kyōraku considered releasing his Bankai, black fissures appeared in the space behind Aizen.
The space shattered, and Ichigo Kurosaki emerged. He took in the scene and his pupils shrank.
"Bankai – Tensa Zangetsu!"
Without hesitation, he released his Bankai. His two Zanpakutō merged into a single, slender blade. Black and red spiritual pressure surged around it as he swung at Aizen.
"Getsuga Tenshō!"
Looking at the incoming black and red slash, Aizen raised his left hand.
BOOM!
A deafening roar echoed through the replica Karakura Town, shockwaves rippled outwards, pulverizing everything in their path.
…
"Hadō #81. Dankū!"
Just as the injured Shinigami braced for the impact, a familiar voice called out. A translucent barrier appeared before them, absorbing the shockwave.
"Captain Unohana!"
They had never been so relieved to see her. As captain of the Fourth Division, her healing abilities were unmatched.
"My apologies, everyone. I was delayed in Hueco Mundo."
Retsu Unohana opened her hands and enveloped the injured Shinigami in individual barriers, green light emanated from them, healing their wounds. This was the pinnacle of her healing Kidō. Even those on the brink of death would recover under her care.
"Don't apologize, Captain Unohana. Your timing is… perfect."
Kyōraku shook his head. He was right. Had Unohana and Ichigo arrived earlier, they would have been caught in Yamamoto's Bankai. Any later, and they might have been too late.
Kyōraku looked towards the sky. Ichigo's power had surpassed all expectations. Kisuke Urahara's contingency plan, should Yamamoto fail, had been to unleash Ichigo upon Aizen. At the time, they hadn't taken the plan seriously. Ichigo, a mere human empowered by Masaki Kurosaki's spiritual pressure, couldn't possibly rival Yamamoto, in whom they held unwavering faith.
Now, however, it seemed that contingency plan might be their only hope.
But even with his newfound strength, Ichigo's chances against Aizen were slim. He couldn't possibly match Yamamoto's power.
…
After the black and red spiritual pressure dissipated, Aizen's unharmed left hand was revealed.
"Ichigo Kurosaki, you haven't disappointed me. But unfortunately, you're too late." Aizen addressed Ichigo, having effortlessly blocked his Getsuga Tenshō. "Had you arrived half an hour earlier, you might have been a worthy opponent. But now…"
Aizen vanished, instantly reappeared before Ichigo and slashed down with his Zanpakutō.
BOOM!
Ichigo blocked, but the force of the blow sent him crashing through several buildings before slamming into the ground.
BOOM!
He emerged from the crater with blood trickling from his lips and his eyes fixed on Aizen.
"You see, Ichigo Kurosaki?"
Aizen opened his left hand, presenting his palm.
"Your strongest attack can't even break my defense. While I…"
He swung his Zanpakutō, unleashing a wave of pressure that shattered the surrounding buildings. Ichigo blocked, but was driven back, his feet dragged across the ground.
"This is the difference between us."
"Ichigo!"
Isshin Kurosaki, Yoruichi Shihōin, and Kisuke Urahara appeared beside Ichigo. He was their trump card against Aizen. They couldn't afford to lose him.
"Kisuke Urahara, it's been a while."
Seeing them, Aizen paused his attack and smiled. "I must say, I'm disappointed. Your progress over the past century has been… underwhelming."
"Aizen, you've grown stronger, it's true. But look at yourself. Are you even still… you?"
Urahara adjusted his hat. Compared to his Shinigami form, Aizen now resembled a Hollow, with his third eye and butterfly wings.
"You misunderstand, Kisuke Urahara."
Aizen spread his arms wide, as if embracing the world. "The essence of this world is the cycle of souls. All life, regardless of its form, is merely a collection of reishi. As I ascend to higher dimensions, I naturally integrate the most compatible reishi, becoming… more perfect. At the pinnacle of my evolution, I will be the ultimate lifeform."
Urahara remained silent. However, judging from his expression, he did not agree with Aizen's explanation.
Aizen, seeing his disapproval, lost his desire to share his vision. After his encounter with the Soul King's will, after realizing the truth of this world, he had been lost. Then, he had stumbled upon Urahara's Hollowfication experiments. The Hōgyoku had been a product of those experiments. Inspired by Urahara's work, Aizen had created his own Hōgyoku, following a similar path.
But to his disappointment, Urahara had chosen a different path, abandoning his research, sealing away his Hōgyoku. Their journeys, once aligned, had diverged.
Aizen had always believed Urahara, of all people, would understand him. But now, he realized they were no longer on the same wavelength. He had ascended, transcending the limitations of both Shinigami and Hollow. Their perspectives were separated by dimensions. Communication was futile.
A profound sense of disappointment washed over him.
"Kisuke Urahara… I'm no longer interested in you." He didn't attack. He raised his hand, preparing to open a Senkaimon to Soul Society.
To his surprise, he couldn't sense the Dangai.
"How… naive." He shook his head, addressing Urahara. "Kisuke Urahara, you've overestimated yourself. Did you truly believe sealing the Dangai would stop me? I can simply return to Hueco Mundo and enter Soul Society from there."
"What?" Urahara was taken aback. He hadn't sealed the Dangai. It had to be the Gotei 13's doing. By severing the connection between the World of the Living and the Dangai, they hoped to prevent Aizen from reaching Soul Society. But…
Before he could finish the thought, a Garganta opened beside Aizen.
"I'll leave you here to ponder your… miscalculation. Await my return. Await the birth of a new god."
As the Garganta closed, Urahara and the others breathed a collective sigh of relief. Facing Aizen in his current state had been overwhelming. But they couldn't allow him to create the Ōken, to usurp the Soul King's position. The consequences were unthinkable.
"What do we do, Kisuke?" Yoruichi asked. The others looked at Urahara, their leader, their strategist.
"We enact the final plan. Captain Shiba, Ichigo's training is in your hands. Tessai, assist him. We'll go to the training ground. Once Ichigo's training is complete, we'll use the Garganta I prepared earlier to enter Hueco Mundo. We'll try to seal Aizen there. If the battle spills over into Soul Society, the consequences could be catastrophic."
Urahara's goal was no longer to kill Aizen, but to seal him. Having witnessed Aizen's resilience, his regeneration, his evolution, he knew killing him was unlikely. He hoped to shatter Aizen's god complex, to introduce doubt. Once doubt took root, the Hōgyoku, manifesting that doubt, would reject Aizen, weakening him. Then, Urahara could activate the Kidō seals he had placed within the Hōgyoku during its creation, finally sealing Aizen away.
"Understood." The others nodded. Only Ichigo, oblivious to the true nature of the plan, remained in the dark. Before he could ask any questions, however, he was swept away towards Urahara's underground training ground.
…
Meanwhile, back in Soul Society…
The barrier Urahara had erected around the hidden training ground masked their presence from the Reigai, but it also prevented Byakuya from sensing what was happening in the Seireitei. He emerged from the underground chamber, relying on his sight to observe the situation.
Renji Abarai, still smarting from his defeat at the hands of his Reigai counterpart, remained below, training relentlessly to avenge his loss. Being defeated by anyone else might have been bearable, but losing to a fake version of himself was humiliating.
To Byakuya's surprise, the Reigai captains seemed to be maintaining the Gotei 13's usual routines. There was no sign of unrest. Most Shinigami seemed unaware that their captains, lieutenants, and even some seated officers had been replaced. The Reigai's objective seemed to be simply to… replace their originals, to assume control of Soul Society.
As Byakuya pondered this, two powerful spiritual pressures erupted from Karakura Town. He looked up with a flicker of hope in his eyes. He recognized the signatures. They were both Zaraki's.
Unlike the other captains, Zaraki hadn't gone to the World of the Living. He had gone to Hueco Mundo to assist Ichigo Kurosaki in rescuing Orihime Inoue.