Several months later, inside the Sekkiseki Laboratory—
Katori Nanatsuki and Aizen Sōsuke stood before a wall covered in panels of Reishi light.
Nanatsuki now had two laboratories. After becoming the Captain of Squad 12, he was granted a new lab within the Department of Research and Development.
However, he hadn't abandoned his original lab, which was built within the Sekkiseki vein.
Certain research projects not suitable for public exposure were still carried out in this secluded facility.
"Sensei, after years of cultivation, the 'surveillance bacteria' can now cover most of Seireitei. Given a little more time, it'll blanket the entire area." Aizen spoke with admiration. "With this, nothing that happens in Seireitei will escape our notice!"
Nanatsuki had acquired the "surveillance bacteria" a long time ago.
These organisms acted like invisible cameras, almost impossible to detect.
However, the original batch was small—far too few for widespread deployment.
But since they were still bacteria, they could be cultivated and multiplied.
After years of cultivation, the surveillance bacteria had reproduced extensively and were now ready for practical use.
The images perceived by the surveillance bacteria were projected onto the Reishi light panels on the wall.
"We won't be watching this constantly. We'd likely miss key intel that way. We need a method to store the memories of the surveillance bacteria. Right now, I'm assigning that development task to you, Sōsuke," Nanatsuki said after a moment of thought.
What appeared on the Reishi light panel wasn't live footage, but rather the current memory of each surveillance bacterium.
However, each bacterium had a very limited memory span—their recollections would be overwritten moment by moment. A dedicated medium capable of storing their memories was necessary.
"That won't be too difficult. I should be able to complete it within a month." Aizen nodded lightly. "By the way, we've recently made some new discoveries regarding the Soul King fragments. Please come with me, Sensei."
Aizen led Nanatsuki down a lift into the lowest level of the laboratory.
The number of research projects being conducted here had increased significantly, and space was becoming insufficient. So they had expanded downward.
The laboratory now consisted of four levels:
The top level was used for rest and training.The second level held the Reishi Shells and half-human, half-Hollow specimens brought from Miyamoto Tetsuya's lab.The third level focused on Hollows and stored their shells, samples, and test subjects.The fourth level housed the most valuable asset in the entire facility: fragments of the Soul King.
The two of them arrived at the fourth floor.
Nanatsuki saw a spirit lifeform lying in a cultivation chamber, its body covered in a white exoskeleton.
"Is that a Hollowfied Shinigami shell?" Nanatsuki sensed with his spiritual perception that the spirit body possessed both Shinigami and Hollow energy.
"Yes, Sensei, you noticed it too—this is a Shinigami shell that has undergone Hollowfication," Aizen confirmed.
"You placed this specimen here… Did you use a Soul King fragment to Hollowfy it?" Nanatsuki quickly grasped Aizen's discovery.
"I extracted a special power from the Soul King fragments. I believe this force can be called the 'Power of the Soul King.' When I injected this 'Power of the Soul King' into the Shinigami shell, it underwent astonishing changes." Aizen's voice was steady. "The surprising part is, this power appears to possess the traits of Hollow energy!"
Aizen couldn't help but begin to question—what exactly is the Soul King?
To his knowledge, Hollows were enemies of both Shinigami and the Soul King. Yet the Soul King's energy exhibited Hollow-like characteristics.
"You've managed to extract the 'Power of the Soul King'?" Nanatsuki looked delighted. "That's incredible news."
Thanks to his guidance, Aizen had come into contact with the Soul King fragments much earlier than he had in the original timeline.
Perhaps the Hōgyoku's appearance would also be advanced significantly.
"The extraction rate is still quite low, but even a trace amount of the 'Power of the Soul King' produces such dramatic effects. I had to use a heavy dose of suppression agents just to stop this Hollowfied Shinigami shell from mutating further. I've already removed the Soul King energy from its body—otherwise, it wouldn't have maintained this form," Aizen explained.
He had destroyed dozens of Shinigami shells before finally mastering the technique to retrieve the Power of the Soul King.
Thankfully, they had acquired plenty of Reishi Shells from Miyamoto Tetsuya. Otherwise, cultivating that many test subjects would have required vast resources.
"So then, what's special about this Hollowfied Shinigami shell?" Nanatsuki asked. He assumed Aizen wouldn't have shown it off without good reason.
"As expected of you, Sensei." Aizen gave a soft chuckle. "Do you remember the 'Shinigami Reishi Vaccine' you gave me a few years ago?"
Nanatsuki recalled it immediately.
It had been a system reward—an experimental vaccine that allowed a Hollow to withstand Shinigami Reishi and undergo Shinigamification.
Nanatsuki had given the vaccine to Nel, enabling her to take on a Shinigami form.
Afterward, a bit of residual fluid had remained in the syringe, which Nanatsuki had handed over to Aizen for further study.
"You're saying the 'Shinigami Reishi Vaccine' is related to the Power of the Soul King?" Nanatsuki asked.
"It's possible that the test subject you obtained back then already had Soul King fragments in their body, which infused the vaccine with traces of the Soul King's power." Aizen pointed at the spirit lifeform in the chamber. "I extracted a substance from this Hollowfied shell that closely resembles the vaccine."
"Oh? So does that mean we can mass-produce the Shinigami Reishi Vaccine now?" Nanatsuki stroked his chin.
Back then, he had made up a casual excuse, claiming the vaccine had been derived accidentally from a Hollowfication experiment and couldn't be replicated.
Aizen hadn't doubted him—instead, he'd taken that explanation and uncovered real clues.
If the Shinigami Reishi Vaccine could be mass-produced, they'd gain the ability to manufacture Visoreds on a large scale!
"Unfortunately, the extracted substance is unstable. I've already tested it—on its own, it has no effect. It still can't trigger Shinigamification in Hollows. The impurities might be the problem. We probably need to develop a neutralizing agent to stabilize it." Aizen shook his head.
"That's still impressive progress," Nanatsuki said with a small smile. "At this rate, Sōsuke, we may uncover the secret of the Power of the Soul King sooner than anyone imagined."
"I feel the same, Sensei. The answer seems just within reach. But the fact that this power contains Hollow traits... it's truly perplexing." Aizen furrowed his brow slightly.
"It's not that strange. Lord Soul King is the master of all three realms. Hollows and Shinigami are both parts of those realms," Nanatsuki said with intent. "Perhaps the Power of the Soul King contains Quincy properties as well."
"The Quincies… they're part of the Three Realms too…" Aizen murmured, deep in thought.