Chapter 100: The Great Spirit Library, Urahara Kisuke's Research Materials

Captain-Commander Yamamoto approved Aizen's request.

Since Aizen was the one who proposed this, and it involved specialized knowledge, the Fifth Division and the Twelfth Division would jointly investigate all of Urahara Kisuke's past experiments.

The goal was to see if they could find any clues from these experiments.

As for the other divisions, they were to strengthen their defenses to ensure such an incident would never happen again.

As for how much pressure Yamamoto would face from the Central 46 upon his return, that had nothing to do with Haruki.

After returning, Haruki and Aizen would head to the Great Spirit Library. The Great Spirit Library was managed by the Amane family, who had served as its chief administrators for generations within the Central 46.

Since this was a legitimate entry, they needed to obtain permission from the chief administrator.

Of course, Haruki didn't need to worry about this.

Dealing with nobles was a task for those higher up.

Once Aizen finished handling the formalities, Haruki couldn't help but smile. "You know, this is the first time we've entered the Great Spirit Library legally."

Aizen smiled but said nothing.

The Great Spirit Library wasn't an easy place to enter, as it contained too many of the Soul Society's secrets.

The Soul Society had far too many unspeakable secrets.

The simplest example was the creation of the Ōken…

You see, what Aizen saw in the Great Spirit Library wasn't the method to create the Ōken, but the process of its creation!

And what was the process of creating the Ōken?

It required 100,000 souls and a spiritually dense area with a radius of one ri!

In other words, long before Aizen, someone in the Seireitei had already done this!

Through special spiritual techniques, 100,000 souls and a spiritually dense area with a radius of one ri could be combined to form the Royal Key, also known as the Ōken.

Of course, there was another way to create the Ōken, and that was by reshaping a Shinigami's body using the Soul King's power. The reconstructed bones and hair of the Royal Guard became the Ōken.

Aizen's plan to create the Ōken using a spiritually dense area and 100,000 souls was essentially an attempt to turn himself into a member of the Royal Guard.

And the Soul Society had clearly done this before.

For example, Captain-Commander Yamamoto knew the location of one Ōken, which likely wasn't the result of being cleansed by the Soul King's power but was instead created using the same method Aizen intended to use.

In other words, the Soul Society had already done this once before Aizen.

The Soul Society had done it too!

However, such things were, of course, not to be disclosed. After all, the propaganda for ordinary Shinigami had to maintain their image of righteousness and pride as the world's balancers. This was necessary to ensure the cohesion of the organization.

This time, their entry into the Great Spirit Library was strictly limited by the chief administrator. They were only allowed to search for records related to Urahara Kisuke. All other records were off-limits.

Such restrictions were meaningless to Aizen, as there was no place in the Soul Society he couldn't access. However, entering openly like this was indeed rare.

The Fifth Division and the Twelfth Division arrived together. When Aizen opened the Great Spirit Library, some technicians from the Twelfth Division and the captain and vice-captain of the Fifth Division entered together.

Aizen and Haruki were there ostensibly because Aizen had proposed the investigation, but in reality, they were there to monitor Mayuri Kurotsuchi.

Although Mayuri was the captain of the Twelfth Division, his behavior and ideas were too dangerous, making him untrustworthy.

Thus, Captain-Commander Yamamoto ordered Aizen to accompany him to ensure Mayuri didn't cause any trouble.

Of course, this couldn't be stated outright, but for Shinigami who had lived for centuries, such things were understood without words.

Upon entering the Great Spirit Library, Haruki couldn't help but want to complain at the sight of its supercomputer-like structure.

The Great Spirit Library was like a supercomputer, but aside from the screens, the surrounding structure was made of wood. It was both advanced and ancient—truly fitting for the Seireitei.

Haruki ignored the Twelfth Division and found a screen to see if there was anything interesting.

Of course, he could only search for Urahara Kisuke's research materials.

Urahara Kisuke was indeed a genius, especially after founding the Research and Development Institute. His creations had exploded in number like a geyser.

Unfortunately, his time as the institute's director was too short—only nine years. If he had stayed longer, who knows how many more fascinating inventions he would have created?

After a while, Haruki even found research related to the Hōgyoku.

If Mayuri saw this, who knew what he would do? But when Haruki looked over, he noticed that Mayuri seemed to completely ignore the Hōgyoku.

With his abilities, it was impossible for him not to recognize the value of the Hōgyoku, yet he casually skipped over it…

This meant…

Haruki glanced at Aizen, who at this moment was standing next to Mayuri, acting as if he knew nothing about research.

Haruki knew that Aizen must have used Kyōka Suigetsu to alter what Mayuri saw.

Haruki stopped worrying about this and focused on reading Urahara Kisuke's research.

For someone aspiring to become a scientist, having access to the research materials of a super-scientist like Urahara Kisuke was incredibly helpful.

He found many inventions and thought that, given time, he could replicate some of them.

After about five minutes, Mayuri suddenly let out a dark chuckle.

"How interesting, Urahara Kisuke," Mayuri said with a cold smile as he looked at the data in front of him. "To think there's something like this."

Curious, Haruki looked over and saw that Mayuri was examining a Hollow.

"This is…" Aizen asked with feigned confusion.

"Hmph…" Mayuri snorted but still explained to Aizen. "This is called a 'Parasitic Hollow,' a special type of Hollow modified by Urahara Kisuke. It can parasitize any spiritual body, and once it does, it completely hides itself."

The Hollow looked like a small snake, and combined with its abilities, it reminded Haruki of the Parasitic Hollow from the Dark Rukia movie.

This Parasitic Hollow actually existed in the main world too?

However, in the movie, the Hollow eventually escaped from the Research and Development Institute. But according to the records here, Urahara Kisuke had deemed it too dangerous and halted the research, even destroying the experimental subject.

"Captain Mayuri, are you suggesting…" Haruki began to ask.

But Mayuri cut him off. "Don't try to guess my thoughts with your limited intelligence! I really don't understand why they sent two people who know nothing about science and technology here!"

Heh, no one in this world understands Urahara Kisuke better than me—well, than Aizen. If not us, who else would they send?

Haruki internally complain but said nothing on the surface.

After all, even Aizen didn't say anything!

Haruki noted down the experimental records of the Parasitic Hollow, planning to try replicating it himself once he returned to Hueco Mundo.

Meanwhile, Aizen focused on the method of extracting foreign objects from the soul, preparing for the eventual extraction of the Hōgyoku from Rukia Kuchiki.

Soon after, Mayuri grew impatient. He seemed to disdain Urahara Kisuke's research and was visibly annoyed.

Haruki noticed that Mayuri became particularly irritated when he saw Urahara Kisuke's research on soul evolution, as if he was deeply dissatisfied with Urahara.

Haruki guessed that Mayuri must have seen parts of Urahara's research that surpassed his own, which was why he was so frustrated.

Finally, Mayuri snorted and left the Great Spirit Library without a word.

Haruki glanced at Aizen, who shrugged innocently.

"Well, that's it for today," Haruki said. "It seems Captain Mayuri has quite a grudge against Urahara Kisuke."

"Did I say that?"

Suddenly, Mayuri turned around and gave Haruki a dangerous look.

"Alright, don't give my vice-captain a hard time, Mayuri," Aizen interjected. "The most important thing now is to address the hidden dangers in the Seireitei and thwart Urahara Kisuke's schemes."

"Hmph."

Mayuri snorted and left with the Twelfth Division's Shinigami.

Haruki shrugged indifferently and followed Aizen out of the Great Spirit Library.

Half an hour later, the captains and vice-captains of the Fifth and Twelfth Divisions gathered in the First Division's meeting room.

Facing Yamamoto Genryūsai Shigekuni, who sat at the head of the table, Mayuri said, "I found something interesting in Urahara Kisuke's research."

He tapped his palm, and a holographic screen projected from his hand.

The data displayed was about the Parasitic Hollow.

Mayuri explained, "First, the 'Parasitic Hollow.' Considering Kyōraku Shunsui mentioned that the attacker wore a Hollow mask, there's a 60% chance it's related."

"Parasitic Hollow?" Yamamoto frowned. "What is that?"

"Can't you tell from the name?" Mayuri said with a hint of malice. "Let me put it simply—perhaps someone in our ranks has already been parasitized."

"Who could it be? Kyōraku Shunsui, who was attacked? Soifon, who was on guard duty? Or…"

"Enough!" Yamamoto barked before Mayuri could finish. "Don't make such claims without evidence."

"What a pity," Mayuri said with a mocking tone. "Those two were the most suspicious."

"Captain Mayuri, you must have found more than just this, right?" Aizen interjected.

"Hmph, then there's this." Mayuri swiped the screen, and the Parasitic Hollow was replaced by a special device—the Tenshintai!

"This is called the Tenshintai, another of Urahara Kisuke's inventions. Its effect is to create a doppelgänger with one's memories and combat abilities for training purposes."

"Hmm?"

"Although theoretically, it doesn't last long, I believe that with some modifications, its duration could be extended. Most importantly, whether Urahara Kisuke used the Tenshintai or not is irrelevant."

Mayuri said coldly, "We only need to know that Urahara Kisuke has the ability to create 'clones' of all of us. That's enough."

His point was clear: whether Urahara Kisuke had used the Tenshintai or modified it further didn't matter. What mattered was that he had the capability to do so!

In such a situation, whether he had done it or not was irrelevant. The important thing was that he could do it!

"What's the solution?" Yamamoto asked.

"The simplest method is to wait for it to dissipate naturally," Mayuri said. "Doppelgängers are just doppelgängers. They can't exist forever. According to the Tenshintai's effects, maintaining a doppelgänger requires a constant supply of spiritual pressure from the user."

"Even if Urahara Kisuke modified it, he couldn't provide 'infinite spiritual energy' to keep them around permanently."

Haruki internally agreed with Mayuri's assessment. As expected of Mayuri, he had a good understanding of Urahara Kisuke's abilities and the nature of various tools.

However, what Mayuri couldn't have anticipated was Rōka's existence.

While it was true that Rōka's creations couldn't exist permanently and would dissipate once their spiritual energy was exhausted, they could last much longer than ordinary doppelgängers.

Combined with the effects of the Hōgyoku, the doppelgängers could exist for an astonishing month!

"We don't have time to wait," Yamamoto said coldly. "Is there a second solution?"

"Have the person maintaining the Tenshintai stop supplying spiritual energy, or destroy the Tenshintai itself," Mayuri said indifferently.

"I'm curious," Aizen said. "Captain Mayuri, you seem to be leaning toward the idea that there's a traitor among us. Why is that?"

"Hmph, because that's the only possibility," Mayuri said again. "Since the attack on the Eighth Division captain, the entire Seireitei has been under my surveillance. Do you think anything could escape my monitoring?"

"From the beginning until now, there hasn't been a single 'new face' in the Seireitei. Do you know what that means?" Mayuri glanced at Aizen.

Aizen remained silent.

Did this mean that the culprit was someone familiar?

Hacking into a specific area's surveillance was one thing, but if the entire Seireitei's surveillance had been compromised, wouldn't that mean the Research and Development Institute was full of fools?

Haruki really wanted to say that if the culprit was Urahara Kisuke, wouldn't it be easy for him to hack into the surveillance system and alter the data?

But if he said that, Mayuri would definitely lose it, right?

Wouldn't that be blatantly saying that his technology was inferior to Urahara Kisuke's?

Yamamoto probably had similar thoughts, but he didn't voice them.

And to be honest, while Mayuri's technology was indeed slightly inferior to Urahara Kisuke's, hacking into Mayuri's system wasn't a simple task.

Especially when Mayuri was already on high alert.