While Aizen was busy with data calculations, analysis, summaries, and various pre-experiment preparations, Naraku Sora focused his gaze on that gemstone.
Although he had seen it many times in the Hueco Mundo laboratory, this was his first time observing it from such a close distance.
If he remembered correctly, the Hōgyoku Aizen created could only be considered a half-finished product.
The other half was created by Urahara Kisuke. Only when the two were combined would it become a truly perfect Hōgyoku.
One that could shatter the boundary between the souls of Soul Reapers and Hollows, and even grant the desires of its user.
Looking at it this way, for the sake of his adopted son's grand ideals, Urahara Kisuke seemed to be an indispensable piece of the puzzle.
*'Besides coercion, is there any other good way to deal with Kisuke?'*
Sora couldn't help but fall into deep thought.
At that moment, Aizen finished his thorough preparations. Just in case, he also set up dozens of layers of Kidō barriers inside the laboratory.
Considering a certain someone's overwhelming performance after Hollowfication, by that logic, no amount of barriers could be considered too many.
Next, Aizen turned his gaze to the figure inside the container.
The former Captain of Squad 10, Umino Unpei.
A special existence who had already broken the soul boundary of a Soul Reaper to a certain extent, and could even actively enter a semi-Hollowfied state.
In terms of pure strength, he was much stronger than those two newly appointed Captains.
He was also the most suitable material for the Hollowfication experiment at present.
Soon, the newly formulated, high-density liquid Reishi was injected into Umino Unpei's body.
When all parameters stabilized, the glowing Hōgyoku slowly descended onto his forehead.
In the next second, an intense Reiatsu suddenly erupted, instantly shattering the sturdy inner walls of the container and sending countless tiny fragments flying outward.
Aizen had long anticipated this situation, so he remained completely unaffected.
He continued to stare intently at the changes in the experimental subject.
The Reiatsu climbed steadily, as if it had no upper limit.
A spiral of light radiated outward with Umino Unpei at the center, almost enveloping his entire body.
Sora watched the scene unfold before him, a thoughtful look flashing in his eyes.
He didn't know if it was just an illusion, but as Umino Unpei began to Hollowfy, he felt like he could hear the intro to the song *Brave Heart* playing in his ears.
It felt as though something incredible was about to emerge.
A massive amount of white, viscous liquid oozed from Umino Unpei's eyes, ears, mouth, and nose, instantly condensing into a pure white, ferocious mask.
It looked just like the Hannya from myths and legends.
The black and white in his eyes vanished, replaced by golden, slit pupils. A hideous and vicious aura permeated the air, instantly enveloping the entire laboratory.
"Na... Naraku... Naraku Sora!"
The exposed teeth parted, and wisps of white steam escaped. The materialized light lingered around Umino Unpei, squirming continuously like a living creature.
"Damn you!!"
Although he had lost almost all of his reason, there was one person he hadn't forgotten—the person he hated most in this life.
The very person who had reduced him to this state: Naraku Sora.
The majestic Reiatsu surged and erupted, turning into a torrent that swept through the laboratory, instantly locking onto the young man standing in front of him.
"The subject's vitals are stabilizing. He won't collapse from the surging Reiatsu in the short term."
"The soul boundary has been completely broken, but his consciousness is basically gone, leaving only pure hatred."
As Aizen stabilized the surrounding Kidō barriers, he spoke calmly, "Sora, although we lack the relevant data, judging from the results, it was your presence that made this Hollowfication experiment a success."
"Just like with Hollows, intense emotion is an indispensable element in breaking the soul boundary."
"Of course, the Hōgyoku needs further improvement. Such unstable factors must be completely eliminated."
Sora grinned, looking incredibly proud.
He heard it loud and clear: Sōsuke just said this experiment couldn't have succeeded without him.
Sure enough, he was the number one intellectual in the Soul Society.
"Haha, you flatter me."
Aizen: "?"
*'Why is this guy suddenly acting crazy again?'*
As the two conversed, Umino Unpei's Reiatsu climbed to its peak, causing the surrounding space to warp with distorted lines as the air vibrated violently.
Exchanging one's sanity for a several-fold, or even tenfold, increase in power.
It was hard to say whether this trade was worth it.
But judging from Umino Unpei's expression, he seemed very satisfied with his transformation.
Because he finally had the opportunity and the power to exact his revenge.
The violent Reiatsu surged and churned, and a blazing pillar of light shot straight toward the ceiling, crashing against the Kidō barriers and emitting a teeth-aching creak.
Feeling the quality of this Reiatsu, Sora couldn't help but click his tongue in amazement.
Compared to the members of the Visored in his memories, the Umino Unpei before him could completely crush them.
He didn't know if Aizen had given him special treatment, or if Muguruma Kensei and the others were just that weak.
Anyway, in terms of Reiatsu, the current Captain Muguruma wasn't even fit to shine his shoes.
Seeing Umino Unpei break free from the original Kidō restraints and charge recklessly toward Sora, Aizen frowned. Just as he was about to release a burst of Reiatsu...
He was beaten to the punch by a certain someone.
A cruel expression hung on Umino Unpei's face. His fist was raised high, all of his Reiatsu converging upon it, blooming with a dazzling light.
Then, without hesitation, he smashed it down toward the figure in front of him.
Feeling the fierce wind rushing at his face, Sora didn't retreat but instead stepped forward. He pulled his arm back, his body emitting a sound like a bowstring being drawn taut.
The moment their fists collided, a mighty roar instantly swept through the room.
Upon contact, a terrifying force surged out. Starting from Umino Unpei's arm, it extended backward with overwhelming destructive power.
Flesh, tendons, and bones all collapsed in an instant.
Half of his body directly exploded into a mist of blood, filling the laboratory.
Watching this exaggerated scene, Aizen's eye twitched, gaining a clearer understanding of Sora's strength once again.
He had almost forgotten.
In terms of pure Reiatsu, this guy might still be slightly inferior to him, but one simply couldn't judge his true strength based solely on Reiatsu.
It directly negated the conclusion he had researched all along:
A battle between Soul Reapers is a battle of Reiatsu.
But upon closer inspection, this guy couldn't exactly be considered a pure Soul Reaper.
Soon, a sharp, grating sound echoed from Umino Unpei's body. The sound of bones and flesh multiplying was like raw iron clashing.
New organs and limbs grew out from the mutilated body.
Hard chitinous bones pierced through the flesh, covering his skin.
As the flesh squirmed, a buffer layer rapidly formed between the exoskeleton and the skin.
His already burly and tall body continued to expand, transforming into a hideous monster several meters tall in the blink of an eye.
"This level of High-Speed Regeneration is almost on par with Arturo."
Sora looked at the giant-like Umino Unpei with some surprise. The surging Reiatsu continuously churned nearby with every breath the monster took.
"And his strength is incredible. He must be at the level of dozens of Kenseis."
The moment his words fell, Umino Unpei threw a sledgehammer-like fist straight down.
The very meaning of his existence was to kill the man etched so deeply into his memory.
Feeling the intense pressure rushing at his face, Sora grinned. He then spread his arms, and countless fist shadows rained down furiously.
There were no techniques, just a pure eruption of straight punches.
A torrential downpour!
In an instant that was difficult for the naked eye to observe, the several-meter-tall giant's body was forcibly hammered into a sky full of blood mist, as if it had been hit head-on by a dump truck running at full horsepower.
In an instant, the thick arms ceased to exist, the chest caved in and collapsed, and more than half of the body was crushed into meat paste.
If he hadn't considered that Aizen might still need to use him later, Sora's fists would have landed on that head covered by the white bone mask.
As one of the outdated bosses, Umino Unpei had indeed received a Hollowfication enhancement.
But compared to a certain player using cheat codes, his power scaling still couldn't keep up.
When Sora pulled his punches, Aizen stepped forward in tacit understanding. He released several Bakudō spells without incantation, instantly binding Umino Unpei in place and even completely suppressing his High-Speed Regeneration.
After briefly checking his soul status and confirming there were no unexpected issues, he looked at the certain someone beside him who was acting as if nothing had happened.
"It's barely a success. Soul suicide won't occur in the short term, which is enough for research purposes for a long time to come."
"Sora, did you feel anything different during this experiment?"
Hearing this, Sora rubbed his fingers together, recalling the sensation of his beatdown just now. After thinking for a few seconds, he said:
"If I had to say, it felt like stuffing the soul of a Menos Grande into a Soul Reaper's body."
"Forcibly stitching two completely different things together."
"Although the increase in strength is massive, it still feels somewhat awkward."
As the first case of perfect Hollowfication in the history of the Soul Society, he had a lot of authority to speak on this matter.
Aizen revealed a thoughtful expression.
Although there was no professional terminology, it still simply and straightforwardly described the crux of the problem.
If they really implanted a Menos Grande's soul into a Soul Reaper's body through the Hollowfication experiment, what kind of result would they get in the end?
Just as he was deep in thought, Sora seemed to think of something and suddenly asked:
"Sōsuke, can you give me a copy of the research notes on the Hōgyoku?"
"Just the defective kind, missing pieces here and there. Preferably a document where even you can't distinguish the key points of the knowledge."
Aizen gave him a strange look. "Why do you want to look at something like that? Aren't you afraid the knowledge will pollute your brain?"
"?"
*'Why is this Sōsuke speaking so harshly?'*
Aizen ignored the guy who was about to throw a fit and walked directly to a corner of the laboratory, skillfully typing away on a keyboard.
Soon, a thick stack of documents spat out from the output slot.
He casually pulled out a few pages and handed them directly to Sora.
"These are some erroneous ideas from the research process, but the overall direction hasn't deviated. It should meet your criteria for a so-called defective product."
"You still haven't said what you want these for."
Sora took the papers and stuffed them into his pocket without even looking at them, grinning.
"I have my own brilliant uses for them!"