Aizen briefly checked Umino Unpei's condition.
Nearly half of his body was gone, having been directly blown into a bloody mist.
Fortunately, his heart and head were still intact. It seemed that Naraku Sora had intentionally held back.
Otherwise, the sheer power of that strike would have been enough to completely erase Umino Unpei from the Soul Society.
However, what surprised Aizen a little was that Umino Unpei didn't look like a researcher at all, yet he had somehow mastered the power of Hollowfication.
Moreover, judging from his physical characteristics, the degree of Hollowfication was quite deep.
During the brief time he spent examining him, the damaged body had already begun to heal rapidly. Although it couldn't compare to Naraku Sora's High-Speed Regeneration, let alone a monster on Arturo's level.
But in terms of recovery speed, it had already surpassed that of an ordinary Adjuchas.
Furthermore, after Hollowfying, Umino Unpei displayed combat prowess that completely mismatched his usual self.
It wasn't just his Reiatsu; even his physical strength had increased by more than a single tier.
He could even tear apart a number eighty-eight Hadō with his bare hands and endure a full-power strike head-on.
Hollowfication truly was miraculous!
However, it seemed to have its drawbacks.
Umino Unpei's performance in battle was noticeably more frenzied, making it almost impossible for him to maintain his usual calm and composure.
It formed a stark contrast with Naraku Sora.
It was no exaggeration to say that Umino Unpei was more like some sort of mindless beast.
The overwhelming power had obliterated most of his rationality, leaving him with nothing but a pure desire for destruction and slaughter.
This was very similar to the results of Aizen's previous research.
A Soul Reaper's soul was actually highly incapable of withstanding the power of a Hollow.
If Hollow powers were forcibly injected into it, it would only lead to the ultimate outcome of soul collapse.
Death was inevitable.
Through calculating countless pieces of data and observing the live example provided by the enthusiastic volunteer Umino Unpei, Aizen arrived at a simple conclusion—
Naraku Sora's Hollowfication was the most perfect and flawless.
It was also the ultimate form of a Soul Reaper who had completely mastered the power of a Hollow.
A truly unique existence in every sense of the word.
Aizen lowered his gaze, his feelings somewhat complicated.
Once upon a time, he believed that someone like him was destined to walk a long, solitary path. Yet, how much time had actually passed? The guy who was supposed to be left in the dust had actually caught up.
From every angle, it was ridiculously absurd.
Aizen shook his head, keeping his inner thoughts to himself. Instead, he focused his attention on Umino Unpei, casting a sealing Bakudō to completely immobilize him first.
Next came the injection of several drugs.
From inert Reishi serums and muscle stiffeners to Reiatsu-binding agents.
These were all developed by Aizen during his free time.
Used individually, their effects were average, but when combined, they could effectively restrain a defenseless test subject.
For a monster capable of casually tearing apart high-level Hadō with his bare hands, one could never be too careful.
"Sōsuke, how did that move look just now?"
Seeing that Aizen had finished his work, Naraku Sora grinned.
"I used that Black Flash to forcefully knock off half of Old Man Yama's beard, establishing a fearsome reputation in Squad 1!"
"I taught you that before."
Aizen nodded. Naturally, he remembered Black Flash.
By controlling the interval between a Reiatsu impact and a physical strike to an almost unobservable margin, it caused an irresistible distortion in space, thereby unleashing destructive power far beyond one's own limits.
He had already tried learning it earlier, but right now, he had only barely grasped the basics.
"Black Flash doesn't really suit me."
Aizen stared at Naraku Sora for a few seconds, then sighed and said helplessly,
"The destructive power caused by my physical strikes and my Reiatsu impacts are too far apart."
"The difficulty of controlling the two to release within a fixed time difference is also quite high. It requires a massive amount of time and energy to practice."
"Besides, I don't really like this style of attacking."
Hearing this, Naraku Sora revealed a look of sudden realization.
'I get it.'
'Aizen thinks close-quarters combat is too unrefined. It doesn't fit his aesthetic as a mastermind behind the scenes at all.'
"Minor issue."
Naraku Sora waved his hand. "Since you understand the principles of Black Flash, you can just innovate. Anyway, no one made a rule saying you have to use your physical body to unleash a Black Flash."
"As long as you fix the time difference between the physical strike and the Reiatsu impact at 0.000001 seconds, it can be considered a successful Black Flash. Later on, I'll try developing a way to release it using a Zanpakutō."
"I'll just teach you once I've completely perfected it."
"Look forward to it, Sōsuke. Once I get some results on my end, I'll let you taste the fruits of victory together with me."
Hearing Naraku Sora's words, Aizen paused, subconsciously imagining the scene of unleashing a Black Flash with a Zanpakutō.
'What is this sudden sense of anticipation?'
'Have I really been infected by this guy?'
Aizen shook his head, tossing this dangerous thought to the back of his mind, and turned to clean up the residual Reishi traces within the Kidō barrier.
Because he had done this many times, the cleanup work was a familiar routine.
After clearing away all traces that could possibly expose their identities, Naraku Sora hoisted the completely sealed Umino Unpei onto his shoulder, and the two returned to the secret base in Mount Koifushi together.
Looking at the burly figure floating in the life-support pod, the corners of Aizen's mouth curled up slightly.
For Arrancars, he already had Arturo, who could provide him with data parameters on Menos Grandes. Now, with the addition of Umino Unpei, he also had the relevant data on Soul Reapers.
Moreover, both possessed the powerful ability of High-Speed Regeneration. Some experiments that couldn't be performed on ordinary living subjects could easily be tested on them.
Aizen seemed to see a smooth and open road ahead for his scientific research.
'The future is very bright.'
Slumped on the sofa, Naraku Sora suddenly looked up and spoke.
"By the way, Sōsuke, do you have any scientific technologies or black tech that are already completed but hold no real value, yet are extremely difficult to research?"
Aizen frowned, not understanding what a brute like Naraku Sora would want with such things.
"I usually don't research things that have no value."
"Why are you suddenly asking about this?"
Naraku Sora grinned and gave a brief description of Kurotsuchi Mayuri, who was currently locked in prison.
"Possessing one of the top five intellects in the Soul Society?"
Aizen looked thoughtful. Based on his understanding of a certain someone, one of those five was probably a guy named Naraku.
"Yeah, yeah. Just keeping him locked up in a cell is a bit of a waste, but killing him feels like an even bigger pity."
Naraku Sora spoke without a shred of self-awareness.
"It would be best if we could take him in and use him for ourselves."
After thinking for a few seconds, Aizen calmly said,
"Since Kurotsuchi Mayuri was locked up by you because he wanted to modify someone else's Zanpakutō, you can absolutely start from that angle."
"As long as you can prove that only you can provide him with an endless stream of research materials and exclusive technology."
"A researcher so loyal to science and the unknown would never betray..."
Naraku Sora suddenly exclaimed in realization,
"I get it!"
Aizen: "?"
'I haven't even explained the specific methods yet. How did this guy already understand? What did you figure out this time?'
But before he could continue explaining, Naraku Sora had already gotten up and left the secret laboratory, impatient to implement whatever method he had just thought of.
Seeing this, Aizen looked exasperated but didn't say anything more, turning his attention back to the life-support pod.
Thanks to a certain someone's help, the available test subjects were now overflowing.
At the thought of his upcoming research, a hint of fiery passion couldn't help but surface in his eyes.
The premise of every plan was built upon ample preparation!
Inside the Hell of Reviving cell in the Shino Prison.
Kurotsuchi Mayuri slowly woke up from his coma, feeling as though there wasn't a single spot on his body that didn't ache. It was as if he had been run over by a steamroller from head to toe.
Even his soul throbbed with an uncontrollable, agonizing pain.
Fortunately, he was already familiar with pain. He only needed to alter the parameters of his blood and flesh to immunize himself against over ninety percent of the severe agony.
Of course, this method only applied to a modified body.
Mayuri closed his eyes and manipulated his Reiryoku with his consciousness, instantly reducing the pervasive, intense pain. His tense nerves also relaxed considerably.
Only after finishing all this did he have the energy to observe his current surroundings.
Bright, clean, spacious, with an independent bathroom...
After getting a clear look at everything before him, Mayuri froze, unable to determine exactly where he was for a moment.
Through the bars of the cell, he clearly saw the thick ink writing on the opposite wall.
"Hell of Reviving, Number 003?"
"After I lost to that guy, I was locked up in the underground prison?"
"Wait, since when did the prison look like this?"
Although he didn't participate much in its management, Mayuri had seen the environment inside here before.
The last time he returned from a mission, the prison was still dark and decaying. How did it turn into this just in the time it took him to conduct an experiment?
Could it be that it was all renovated by that Third Seat named Naraku Sora?
Countless doubts surged in Mayuri's heart.
But they were immediately replaced by intense anger. A mere Third Seat actually dared to commit insubordination! Not only did he attack him without authorization, but he also locked him up in a prison cell.
'Once I get out of here, I'll definitely make that guy pay!'
Just as his emotions were fluctuating, the sound of a conversation suddenly came from the end of the corridor.
Mayuri subconsciously closed his eyes, pretending to be unconscious again.
To make it look more realistic, he even actively controlled his blood flow and breathing rate, making himself indistinguishable from his previous state.
"Mr. Urahara, are you sure you want to do this?"
Two figures strolled down the corridor, one of the voices asking in confusion.
"Muramasa can indeed materialize Zanpakutō, but his memories from the rebellion period will still be retained. If we do something bad to him..."
Another voice chimed in, "Actually, I was also influenced by that Mr. Kurotsuchi. I realized that besides communicating with a Zanpakutō, experimenting on it is also a viable method of training."
"Anyway, the ultimate goal is to understand the Zanpakutō better."
Kuchiki Kōga nodded. "That makes sense."
After the footsteps faded away, Mayuri slowly lifted his eyelids, a hint of unconcealable fiery passion flashing in his golden eyes.
"Muramasa?"
"Researching a materialized Zanpakutō?!"