"From the very beginning, I couldn't sense its Reiatsu at all."
Aizen crouched beside the monster's corpse, expression grave.
"Judging from the outer 'steel skin,' it should be a Hollow. But at the level of the soul, it's a normal Shinigami soul."
"And that soul's been modified, giving it extremely strong concealment abilities."
"The source of that ability is very likely its Zanpakutō."
He didn't press Naraku any further—everyone had their own secrets, himself included.
Even if they'd been inseparable and honest about everything back at the academy, once they joined the Gotei, their relationship had changed.
The past was the past; people had to live in the present.
There was no way Aizen could involve Naraku in his plans. If he did, the most likely end would be that they turned on each other.
Naraku, meanwhile, had a look of sudden realization. "So you stuff a Shinigami's soul into a Hollow's body, fuse the two powers together, and end up with a monster like this."
Aizen glanced at him in mild surprise. "It's a bit of a stretch, but… you could put it that way."
"A man-made monster."
Naraku's face turned serious, and he finally understood why he'd been able to smell that thing.
Because in a sense, he and that thing were the same kind.
Both had Hollow power—and both had a bright future ahead of them.
Then, under Aizen's puzzled gaze, Naraku looked at him with deadly seriousness:
"Aizen, you should be able to track down the mastermind, right?"
As if afraid Aizen would refuse, he hurriedly added:
"This is my one and only request in this life as your best friend. You have to say yes."
Aizen: "…"
He had no idea what kind of nonsense this guy was spouting this time.
But he'd heard some version of this same line countless times back at the academy.
Buying lunch, skipping class, tutoring after hours, sparring practice—you name it, if it involved asking for something, Naraku would slap "my one and only request" on the front.
Naraku was nothing but trouble, yet oddly, Aizen didn't find it annoying.
Because he could feel it clearly—that pure, completely selfless friendship with no hint of ulterior motive.
Maybe that was just the simplicity of student days.
Countless images flashed through his mind, and after a short pause, Aizen nodded.
"I'll try."
Naraku grinned. "That's the best friend I recognize. Next time I'll bring you some of the Central Prison cafeteria's special dishes."
Aizen turned back to examining the deformed corpse whose skull had been blown apart.
It had both Hollow and Shinigami traits, yet truly belonged to neither. On a technical level, it could only be called a failed product.
But its existence still gave Aizen a certain inspiration.
He hadn't yet grown to his true limit, but he could already see that future.
If he wanted to change this rotten world, breaking past the limits of a Shinigami was something he had to do.
Maybe this data would come in handy.
With a calm expression, Aizen dismembered the body, letting blood soak his hands as slick organs slid between his fingers.
He was searching for any trace of the method used.
All technical modifications left marks; no matter how brilliant the scientist, they weren't exempt.
It didn't take long for him to find something.
"There's Reiatsu in the heart that doesn't belong to this creature at all. Most likely, it's connected to the mastermind."
As he spoke, Aizen dipped his fingers in some blood and began drawing symbols on the ground.
"Heart of the south, eyes of the north."
"Fingers of the west, foot of the east."
"arrive with the wind and depart with the rain! Bakudō #58, Kakushitsuijaku!"
The moment he finished, countless threads of reishi shot up from the symbols, spreading outward at a speed the naked eye could barely track, racing off to the horizon.
Aizen stood up and looked in the direction the reishi threads had vanished.
"Let's go. If we follow Kakushitsuijaku's guidance, we should be able to find whoever's behind all this without much trouble."
...
...
As one of Soul Society's core components, Rukongai's souls came from all over—even from different eras.
Not just local residents.
The population was so massive it was impossible to count. Searching soul by soul would be like looking for a needle in a haystack, enough to make any investigating Shinigami despair.
Especially a battle junkie like Naraku, who wasn't exactly a strategist—he had nowhere to even start.
Fortunately, he had a good friend.
Following Kakushitsuijaku's guidance, the two tracked the trail all the way to West Rukongai District 12, Yanbara.
Eventually, Naraku stood on a bustling street, looking into the distance where the reishi threads had faded out.
There, standing tall like a crane among chickens, was a particularly exquisite building. Pink lanterns swayed in the wind, and ambiguous, "chicken-crowing" sounds echoed nonstop.
It was a high-end pleasure house—one Naraku had never visited since coming to this world.
Seductive music drifted out from within, and through the gaps he could faintly see beautiful women in loose kimono clinging to their clients, laughing and flirting.
Seeing this, Naraku cracked his knuckles, clearly eager.
Aizen went silent again.
The last place he'd ever expect the mastermind behind such a creature to be hiding… was a place like this.
He raised a foot to leave, but was grabbed by the wrist before he could move. Naraku, quick as ever, held him in place and said earnestly:
"Brother, running away before battle isn't your style."
"You don't want to see the mastermind walk free, do you?"
"I'll stand watch outside," Aizen tried one last time to bargain.
Naraku refused on the spot. "No way. What if there's someone in there I can't handle? If we're together, at least we can cover each other."
As he spoke, he was already dragging the good-natured Aizen toward the den of corruption—
The Pleasure House of Elysium.
Silhouettes filled the corridors inside; everyone was busy with their own business, and nobody noticed two Shinigami slipping in.
Naraku moved like a seasoned regular. With a casual wave, he called over two pretty geisha.
"Give us a quiet private room. It's my brother's first time here."
Realization flashed across the geisha's faces. They immediately took the lead, guiding the two of them deeper inside.
Aizen opened his mouth, then closed it again. Everything he wanted to say turned into a helpless sigh.
If word of this day ever got out, he'd really have to build a new public image for himself.
But since they were already this far in, work came first.
After a few corridors, the geisha led them to a very secluded private room.
As soon as they stepped inside, Naraku reached out with his "dishonest" hand and chopped both women on the neck with a quick hand strike.
Once they were down, he turned to Aizen with a righteous look.
"Come on. Time to get to work."
For some reason, Aizen actually felt relieved at the sight and immediately cast Bakudō #58: Kakushitsuijaku again. Threads of reishi shot through the wall, all pointing westward.
The two suppressed their Reiatsu and followed the indicated direction,
until they reached a faintly glowing Kidō barrier.