Since Hui's disruptive visit, this was the first time all the captains of the Gotei 13 had assembled.
However, three individuals were conspicuously absent: Aizen Sosuke, Gin Ichimaru, and Tosen Kaname.
They had betrayed Soul Society.
According to intel, Aizen had become the ruler of Hueco Mundo, standing firmly in opposition to them.
Truthfully, even with Aizen as the Hueco Mundo sovereign, Yamamoto hadn't considered him a significant threat. If things continued as they were, Yamamoto was confident he could effortlessly crush Aizen.
Of course, this premise was based on Hui not mentioning that Aizen, after merging with the Hogyoku, would possess the qualifications to become his adversary.
After Hui's declaration, Yamamoto understood: Aizen Sosuke, the Hueco Mundo ruler, was fundamentally different from Captain Aizen Sosuke.
Yamamoto was well aware of Hui's immense power.
Although Yamamoto hadn't released his Bankai in their previous encounter, Yamamoto knew that even his own Bankai might not inflict any harm upon Hui.
The reason was simple: spatial manipulation.
Spatial abilities were inherently overpowered, especially when combined with Hui's illusions, swordsmanship, physical prowess, and Reiatsu.
To a certain extent, Hui was invincible to them.
Yet, Hui, a genuine powerhouse, had explicitly stated that Aizen, after fusing with the Hogyoku, would become a worthy opponent. This spoke volumes about Aizen's post-Hogyoku power.
Aizen alone was now a force to be reckoned with.
However, from Unohana Retsu, Yamamoto heard another name, familiar yet distant:
Yhwach!
A tremendously powerful Quincy who, a millennium ago, led his forces in an assault on Soul Society.
Although Yhwach was defeated and sealed by Yamamoto, the old captain never underestimated him.
He knew that if he hadn't been in his prime during that ancient war, the outcome might have been different.
Fortunately, Yamamoto had emerged victorious.
Yet, even in victory, Yamamoto couldn't kill Yhwach, only seal him away.
He had sealed Yhwach's heartbeat, consciousness, and power, believing that Yhwach would eventually perish over the long passage of time. He hadn't worried about it since.
However, judging from Hui's words, the seal on Yhwach had utterly failed.
If it were only Aizen, or only Yhwach, Yamamoto might not be concerned. But facing both simultaneously... The situation was undeniably grave.
He had such a personality. Because he was too powerful and farsighted, he often overlooked crucial details, ultimately leading to numerous calamities.
Shiba Isshin's report about modified Hollows appearing in the World of the Living, coupled with Mayuri Kurotsuchi's dismissed report on the potential future impact of Quincies on soul balance, resulted in a missed opportunity to predict and prevent Aizen's betrayal and Yhwach's resurgence.
It was regrettable, but no one was perfect.
However, faced with the mysterious Hui, an insurmountable force, and with Hui himself acknowledging Aizen and Yhwach as worthy adversaries, Yamamoto finally recognized the gravity of the situation.
Once all the captains were seated, Yamamoto wasted no time and addressed the assembly directly: "I have summoned you all for a matter of utmost importance. Captain Unohana, please share the information gathered from your visit to the World of the Living and Hueco Mundo."
Yamamoto gestured towards Unohana Retsu.
She nodded and proceeded to recount the events in the World of the Living and Hueco Mundo to the assembled captains.
Naturally, she omitted her own ambiguous interactions with Hui, focusing instead on the information gleaned from him.
She emphasized their encounter with Aizen in Hueco Mundo and Hui's assertion that Aizen, after merging with the Hogyoku, and Yhwach, would be strong enough to challenge him.
The captains were stunned by Unohana's account.
Even though Aizen had previously hypnotized them all, they hadn't perceived him as being all that powerful.
After all, in the long years past, the strength Aizen displayed was never truly top-tier among them.
Now, however, Aizen had become the ruler of Hueco Mundo.
Moreover, according to Unohana, Aizen's current power alone was sufficient to effortlessly suppress all the captain-level Shinigami.
"The Hogyoku... Aizen Sosuke... is he really that strong?" Soi Fon murmured to herself, filled with doubt.
"His current strength undoubtedly surpasses ours. And he hasn't even reached his peak yet. According to Hui, Aizen has only partially fused with the Hogyoku. Once the fusion is complete, he will transcend the limitations of Shinigami and reach another dimension in power entirely," Unohana explained, her tone grave.
Even the current Aizen was capable of defeating, or even killing, her.
Once Aizen fully merged with the Hogyoku, perhaps no one in Soul Society, besides Yamamoto, could stand against him.
"So, are we going to Hueco Mundo to apprehend the traitor?" Komamura Sajin, the Captain of the 7th Division, asked, looking at Yamamoto.
The other captains followed suit, awaiting Yamamoto's command.
However, Yamamoto responded, "This is not just about Aizen. You have all overlooked another individual: Yhwach."
Yamamoto's aged eyes swept across the assembled captains, each gaze carrying an immense pressure. "A thousand years ago, the Quincy waged war against us, led by their king, Yhwach. He was an individual with powerful and peculiar abilities."
Yamamoto's eyes glazed over slightly, seemingly lost in memories of the past. He refocused and continued, "In that war, we...hah, In the end, I sealed Yhwach's heartbeat, consciousness, and power."
Yamamoto began to recount the events of the thousand-year-old war to the captains.