The Research and Development Bureau was a new department.
It was only established after Kisuke Urahara took office.
Here, there were even more bizarre individuals than Shinji Hirako.
People with horns growing out of their heads, others wearing strange golden masks dancing around—these were the relatively normal ones, still vaguely human in form.
Naruto even saw a green catfish operating a computer.
Their attitude toward Kisuke Urahara was strange.
There was no respect one would expect from subordinates toward a captain; they were all preoccupied with their own work.
Kisuke Urahara didn't bother greeting them either. He simply led Naruto and Yoruichi Shihōin to the deepest level of the bureau.
A vast, empty, desolate area.
Naruto was a little shocked.
Such a massive underground space, with even a false sky above—it was like another world entirely.
He was also confused.
Why bring him here?
This place resembled a training ground. If the goal was to examine his body, the upper levels equipped with precise instruments seemed more appropriate.
"Let me introduce this place, little Uzumaki," Kisuke Urahara spread his arms with pride. "This was the first project I completed after founding the Research and Development Bureau."
"Here, we can avoid any surveillance from the Seireitei."
"Even the Central 46's restrictions on captains don't apply."
"Even a Bankai can be released without being noticed."
Naruto frowned.
That sounded even less like it was for "research."
"The seal on your body is quite fascinating," Urahara leaned in closer, "Neither Shinigami, Hollow, nor Quincy…"
"It's completely different from any spiritual techniques used by the spiritually aware humans in the living world."
He paused, scrutinizing Naruto.
Originally, he hadn't planned on getting involved with Naruto.
He only took up Unohana's request out of standard camaraderie.
But...
As his research into the "seal" deepened, and after probing Shinji Hirako for intel on Naruto...
He couldn't suppress the desire to study the mysterious power within Naruto.
It bore a curious similarity to a technique he was developing.
He continued, "That sealing method's manipulation of spiritual energy is rudimentary—superficial, really—but its application to bodily transformation is remarkably intricate."
"Its effectiveness rivals that of our Shinigami techniques."
"Such a unique concept and approach—it's an area we've never explored."
"Unfortunately, all I have is the transcription Captain Unohana gave me."
Naruto lifted his shirt. "Want to take a look?"
"I'm fine with it."
"No, no, no," Urahara shook his head rapidly. "The external markings are meaningless. I want to understand the operational core."
"So…"
"Let's fight!"
Naruto blinked. "Huh?" The shift was too abrupt; he couldn't quite process it.
"Combat. Release your sword and fight," Urahara said with enthusiasm and decisiveness. "Push yourself until you lose control."
"I'll record all the data and analyze the seal on your spiritual energy."
Naruto hesitated.
Yoruichi pressed down on his head. "Kid, if you're losing control, it means you're still unfamiliar with your power."
"You'll get better by using it more!"
"And don't worry about hurting us. Don't let Urahara's carefree look fool you—he is a captain."
Urahara smiled. "And down here, we're unrestricted."
Naruto no longer hesitated. He nodded and drew his sword. "Then I'll be in your care, Captain Urahara, Captain Shihōin."
He chanted the release.
The ominous, feral spiritual pressure of the Nine Tails surged forth.
Quickly, four tails emerged. He lost all reason, rampaging in madness.
When he came to—
Naruto found himself in a hot spring.
Yoruichi was naked beside him, her body bearing some bruises and scratches. She greeted him cheerfully as he woke, "Yo, awake? You really went wild back there."
She was completely nonchalant.
Naruto blushed, flustered, and quickly averted his gaze.
He had a jutsu that mirrored this kind of scene, but… doing it himself was one thing. Being in the same hot spring as her was something else entirely.
As a young man, he'd never faced this kind of situation before.
Kisuke Urahara was crouching by the hot spring, eyes sparkling as he looked at Naruto. "Your body's almost fully recovered?"
"Can you release it again in a bit?"
"I got some interesting data, but it's still incomplete…"
Yoruichi, clearly annoyed, splashed hot water at him. "Think about me too, will you? My stamina isn't as boundless as this brat's."
That day—
Naruto lost control and transformed four times.
Kisuke Urahara was thoroughly satisfied and arranged with Naruto to do similar tests twice a week.
As for compensation—
He would provide all his research results related to the seal.
And Yoruichi would give Naruto lessons in Hakuda (hand-to-hand combat).
As the most physically skilled among the twelve captains, her training proved immensely beneficial to Naruto.
Two months later—
Kisuke Urahara unveiled his first breakthrough.
On top of Naruto's original seal, he added two additional incantation barriers.
With no errors.
The results were remarkable.
Naruto could now maintain his sanity even while using four tails. Only upon manifesting the fifth tail would he lose control.
And the "Five Tails" state brought Urahara immense surprise.
When Naruto lost control, a white bone-like mask began forming on his face.
At first, Urahara thought it was a Hollow mask. But when he and Yoruichi cut off a portion of it, they discovered it wasn't.
It was simply "bone"—completely different from Hollow powers.
Still, it gave Urahara new ideas for his research.
However…
The power of the "incantation" seemed limited.
Even with more auxiliary techniques added, Naruto couldn't retain his sanity in the "Five Tails" state.
Urahara grew anxious.
He was desperate to see what "Six Tails," "Seven Tails,"… even "Nine Tails" would look like.
This sword named "Nine Tails" was unimaginably powerful.
Most of the time, it was Yoruichi who sparred with Naruto, though Urahara occasionally stepped in to collect data personally.
Both concluded the same thing:
A "Five Tails" Naruto already had the strength of a top-tier lieutenant.
If he could reach "Six Tails," he'd be equivalent to a mid-tier captain—around the level of newly promoted Captain Kensei Muguruma.
Following that logic, even just his Shikai could potentially place him among the top captains.
But no matter how eager Urahara was, he knew his limits.
Whenever Naruto showed signs of further losing control—when a new tail was about to emerge—Urahara would immediately seal his spiritual flow.
All research was done under the condition of ensuring Naruto's safety—and their own.
Amid training, learning, and experimentation, time flew by.
At the academy's training ground—
Sōsuke Aizen was teaching Naruto how to cast Hado spells above number fifty, when he suddenly remarked, "Graduation season is here again."
Naruto blinked, dazed. "Yeah… graduation."
He looked off into the distance—cherry blossoms were once again in full bloom.
"Have you decided which squad you want to join?" Aizen asked.
Naruto shook his head. "Isn't it assigned after we apply?"
"That's for regular students," Aizen smiled. "You're different. You're a genius."
"Even Captain Hirako is trying to recruit you."
Naruto thought aloud, "Squad Five, huh…"
"But speaking of which—aren't you going to the living world soon for Konso training with the sixth-years?" Aizen suddenly changed the subject, seemingly trying to avoid putting pressure on Naruto.
Naruto nodded and grinned. "Yeah, Director Bogang told me about it."
Konso was the ritual for Shinigami to help souls pass on to the Soul Society.
Every Shinigami had to master it.
Naruto was no exception.
He was looking forward to the field training in the human world.
Maybe then he could uncover why he kept inexplicably shifting between "Konoha" and the "Soul Society."
The ritual was simple. The excursion to the human world was more symbolic—signifying that students were stepping out of the academy, ready to stand on their own as full-fledged Shinigami.
"I wish you success," Aizen offered his blessing. "But with guidance from Captain Urahara and Captain Shihōin, I doubt you'll have any problems."
Naruto grinned wider. "And from Vice-Captain Aizen too!"
"If it weren't for you, I wouldn't believe I could learn such high-level Kido!"
"Just call me Sōsuke, we're friends," Aizen's tone was gentle and slow. "I'm just a vice-captain, no match for those two captains."
"But… Naruto-kun, your recent progress has been astonishing. Did they teach you something new?"
Naruto scratched his cheek. "Sorry, Sōsuke. Captain Urahara told me I can't tell anyone about that."
Aizen apologized, "My bad—I spoke out of turn. Guidance from a captain is rare. Be sure to cherish it."
(End of Chapter)