The truth about the Soul King's current state had completely shattered Aizen Sōsuke's understanding of the world.
It was vastly different from what he'd learned in the Shin'o Academy textbooks.
The Soul King—the divine being who created the Three Realms—was said to possess supreme might. Both the Gotei 13 and Central 46 were built on the foundation of his rule.
A seed of doubt quietly took root in Aizen's heart about the legitimacy of the Soul Society's system.
'If the Soul King has become nothing more than the Linchpin of the Three Realms… does he even have the right to rule anymore?'
But Aizen was cautious by nature. Knowing that their conversations might be perceived by the Soul King, he kept those thoughts buried deep within.
"Sōsuke, put aside what you're doing for now. We're going to the Shiba Clan archive," Nanatsuki said with a smile.
After returning from Muken, he had infiltrated the Great Spirit Book Gallery to look up information on the sealing technique inside Muken.
The Gallery documented Soul Society's history and recorded most major events.
But the seal in question likely existed even before the Soul King created the Three Realms, so the gallery held no detailed records.
That led Nanatsuki to recall the Five Great Noble Houses, whose ancestors were present before the current world order.
Back when the Soul King split the chaotic primordial world into the Soul Society, Hueco Mundo, and the World of the Living, he had done so by using his omnipotence as a wedge.
The five founding ancestors of the Five Great Clans had participated in and witnessed this process.
The Shiba Clan was one of those five houses. With its long-standing lineage, its archives might contain the information Nanatsuki sought.
"You want to go to the Shiba Clan, Sensei?"
"Yes. I want to look through some ancient records, but I've never been there before, and navigating it on my own would be difficult. You're already familiar with it—take me to their archive."
"No problem. I'm very familiar with their library."
Though Shiba Isshin was Nanatsuki's disciple, he was still young and hadn't become head of the family. He didn't have the authority to grant access to their private records.
That's why Nanatsuki decided to ask Aizen, who had already snuck into the Shiba archives, to guide him and save the trouble of navigating blind.
A short time later, the two arrived at the Shiba estate.
"The Shiba Clan isn't very populous these days…" Nanatsuki murmured, scanning the spiritual presence within the estate.
"That's true. Not only are there few clan members, but even their servants are fewer than those of lower-ranked noble families in the Noble District," Aizen nodded.
The Shiba Clan had been in decline for years, and hadn't produced a captain-level Shinigami in quite some time.
What's more, they no longer resided in the Noble District but in Rukongai.
This had caused them to gradually fade from prominence among the Shinigami.
At this rate, the Five Great Noble Houses might soon become Four.
Nanatsuki and Aizen bypassed the walls and quietly entered the courtyard.
A graceful woman in white was tending to the garden, unaware of their sudden appearance.
"I've already used Kyōka Suigetsu to manipulate her perception. She won't notice us," Aizen said calmly.
He had grown close to Shiba Isshin and often visited him at the estate.
Those visits had given him plenty of chances to demonstrate his Kyōka Suigetsu—a water-type Zanpakutō—to the other Shiba clan members.
By now, almost everyone in the Shiba household had seen his Zanpakutō in action.
"An impressive ability," Nanatsuki remarked with a nod.
Aizen's talent was undeniable. His Reiatsu had already grown strong enough to approach captain-level.
The hypnotic effect of Kyōka Suigetsu was powerful enough that most Shinigami couldn't detect anything unusual.
Everyone they passed failed to notice them, even when the two spoke aloud in their presence.
Thanks to Aizen's familiarity, they quickly reached the Shiba Clan's archive.
"This is it, Sensei—Shiba's archive. What kind of records are you looking for?" Aizen asked.
The Shiba Clan's collection was massive, and searching it would take time even after arriving.
But Aizen had visited many times and was well acquainted with the general layout and classification system of the books.
"I'm looking for information about the Soul King. I suspect the seal in Muken was created by him."
Only the Soul King, Nanatsuki reasoned, could have created a sealing technique that connected Hell and the Soul Society.
"I know exactly where that section is. I've been reading up on it myself. Please, follow me."
The Shiba archive spanned multiple floors, each filled with thousands of spiritual books.
Like all texts in the Soul Society, these were made from Reishi and preserved via specialized Kidō techniques.
Without that, maintaining such a vast library would require tremendous manpower.
After a while, they arrived at the seventh floor.
"This level holds records related to the Soul King," Aizen explained.
"You probably know this archive better than Isshin himself," Nanatsuki noted.
"He hasn't even spent a few days here total. I've already exceeded that easily," Aizen replied with a smile.
Shiba Isshin was still young and far too restless to spend time reading books.
He would rather train for hours than sit still and read for even a few minutes.
"The books here are organized chronologically. Which time period are you looking for?" Aizen asked.
"When the Soul King created the Three Realms—and anything before that."
"If we use the Soul King's creation of the realms as a benchmark…" Aizen walked over to a particular shelf. "The relevant materials should be here."
Nanatsuki approached and began reading.
Aizen didn't idle either—he browsed for records that interested him.
Eventually, Nanatsuki came across a book that contained references to the Muken seal.
The book read:
"This technique was created by the Soul King to maintain world stability.
There are three such techniques—one in the Soul Society, one in the World of the Living, and one in Hueco Mundo."
It also mentioned that the balance of souls between the realms was maintained by the Soul King as the Linchpin of the Three Realms.
Outside these realms, however, was Hell.
Hell had existed long before the Soul King's creation of the current world.
He had placed three spells in the primordial chaos—at three locations—and from those formed the three worlds.
These three formations balanced Reishi between Hell and the Three Realms, allowing spiritual energy to circulate and maintain stability.
Nanatsuki kept reading and found specific details about the locations of the three spells:
The Soul Society's was located in Muken—which he had already verified. The World of the Living's was in Karakura Town, a spiritual hotspot. Hueco Mundo's was deep within the Forest of Menos.
However, there was no mention of what was being sealed in Hell.
He moved on to other books.
Several hours later, he found another tome that described the legend of the Lord of Hell.
Like the Soul King, the Lord of Hell had existed before the Three Realms were formed.
He was immensely powerful and an enemy of the Soul King.
He had created a realm called Hell using the souls of countless sinners from the chaotic world.
In the end, the Soul King defeated him.
His body was split into three parts and sealed in three separate locations within Hell.
This legend, however, made no mention of the sealing techniques in the Three Realms.
If Nanatsuki hadn't witnessed the seal in Muken firsthand, and if Saitō Seiko hadn't confirmed its counterpart in Hell, he would never have connected this story to the earlier records about the Soul King's balancing techniques.
Perhaps the original chroniclers hadn't realized the two were related.
In truth, the three balancing seals created by the Soul King and the three seals that held the remains of the Lord of Hell—were one and the same.
Unfortunately, Nanatsuki couldn't find any mention of where the three seals in Hell were located.
The book he read was written as a retelling by one of the Shiba Clan's ancestors, who claimed to have learned the story from the Soul King himself.
Nanatsuki memorized everything from both books and continued searching for more.
He wanted to know where the three sealing sites in Hell were located.
The Lord of Hell's consciousness was already beginning to awaken—and his full return was only a matter of time.
As the Soul King's enemy, he was unlikely to be friendly toward the Three Realms.
Nanatsuki believed that sooner or later, the Three Realms would have to face the crisis of his return—and it was crucial to understand him better.
Regrettably, after combing through the entire shelf, he found nothing else related.
"You didn't find what you were looking for, Sensei?" Aizen asked, noticing his disappointment.
"I did uncover some secrets," Nanatsuki replied quietly. "But I still haven't found a few key details."
"You remember the Gate of Hell that opened in Rukongai during the summer?"
"Of course. That even made its way to the Academy. A lot of students were talking about it when school started again," Aizen said.
Captain Commander Yamamoto hadn't ordered a cover-up.
Once the meeting was over, the vice-captains and officers had learned about it—and word spread quickly.
Many students had relatives or acquaintances among the Shinigami, so news like that naturally became hot gossip.
"This event has deep implications," Nanatsuki said. Aizen was well-read and curious by nature. There was a good chance he'd stumble across some obscure clue in an unexpected place—so Nanatsuki decided to let him in on the full story.
"In the ancient era before the Three Realms, the Lord of Hell was the Soul King's enemy."
"Even after being defeated, he didn't perish completely."
"The Soul King sealed him instead."
"I found an ancient record mentioning that the Lord of Hell was sealed within Hell—but it didn't specify where. If you come across anything, let me know."
"You may not realize this, but the Gate of Hell opening in Rukongai wasn't just some random phenomenon—it was part of a plan."
"A plan to prepare for resurrection."
"And if he returns… the Three Realms, created by the Soul King, might not survive it."
"This matter runs that deep…" Aizen nodded solemnly. "I'll keep an eye out for anything relevant."
Though still unfamiliar with Hell, he now planned to investigate it further.