Soul Society, Seireitei.
Aizen wore his usual warm, gentle smile as he leisurely left the Fifth Division barracks.
"Captain Aizen!"
As he walked through Seireitei, every Shinigami he passed stopped to greet him.
It had to be said—Aizen played his current role exceptionally well.
To everyone around him, he was an easygoing, approachable captain who treated people kindly regardless of rank.
Thanks largely to that reputation, the Fifth Division had become one of the most popular choices among prospective Shinigami hoping to join the Gotei 13.
But ever since returning from Hueco Mundo, Aizen's thoughts had remained focused on Cyrus.
More specifically, on how to test him.
'That man…'
Aizen continued smiling and nodding politely to the Shinigami around him while considering his options.
Simply hypnotizing a few ordinary Shinigami and sending them into Hueco Mundo to die would accomplish nothing.
Cyrus was dangerous enough that even Aizen himself had felt an overwhelming sense of threat in his presence.
Sending disposable soldiers against someone like that wouldn't even provide useful information.
He needed someone strong enough to force Cyrus to reveal something meaningful.
Still thinking, Aizen eventually arrived outside the Twelfth Division barracks—the headquarters of the Department of Research and Development.
Captain Kurotsuchi Mayuri was an eccentric, an obsessive scientist whose behavior was difficult for most people to tolerate.
But anyone capable of succeeding Urahara Kisuke as captain of the Twelfth Division naturally possessed extraordinary ability.
Aizen wasn't stopped at the entrance.
He had clearly arranged the visit beforehand, and one of the division members led him directly to Mayuri.
"Captain Kurotsuchi."
Aizen greeted him with his usual mild smile.
Mayuri showed no interest in returning the courtesy.
"I looked through the records concerning what you asked about. There's no documentation of anyone like that."
He glanced toward Aizen.
"What I'd like to know is where exactly you encountered such a person. I wouldn't mind seeing them for myself."
"I happened across some information and became curious."
Aizen shook his head as though the matter were trivial.
Mayuri wouldn't work.
His behavior was too conspicuous and too predictable.
If he suddenly entered Hueco Mundo without a proper reason, too many people would notice.
"Could it have been a Quincy ability?"
Mayuri clearly didn't believe Aizen's excuse, but he didn't press the issue. Instead, he turned back toward his work.
"No."
The answer came immediately.
Aizen's eyes shifted slightly behind his glasses.
"Then is it possible for two Zanpakutō to possess exactly the same ability?"
"How could they?"
Mayuri turned around again, visibly irritated.
"You're a captain. Do I really need to explain something this basic to you?"
"Common knowledge has been proven wrong before."
Aizen's smile never changed.
"There's always a first time for everything."
"At most, two Zanpakutō might possess similar abilities. But a Zanpakutō's power originates from the soul of its wielder. For two abilities to be completely identical, the two souls themselves would need to be identical."
Mayuri's impatience was obvious as he continued.
"And even artificially created souls cannot be made perfectly identical."
"What if it isn't the power of a Shinigami?" Aizen asked.
Mayuri stopped.
Then he slowly turned and stared at Aizen without expression.
"Isn't that exactly what you asked me about in the first place?"
His eyes narrowed suspiciously.
"You seem unusually interested in this. Are you sure you merely found some obscure record somewhere?"
"I suppose I've had too much free time lately."
Aizen waved a hand lightly, brushing the question aside.
Mayuri continued studying him for a moment before speaking.
"There are no records of such a power, but that doesn't mean it can't exist. I'd need to examine it directly before saying anything useful."
Then he dismissively waved Aizen away.
"If you actually find something, come back. Otherwise, stop wasting my time."
Aizen didn't argue.
He simply turned and left.
Only after he was gone did Mayuri look toward the doorway again.
"Could such a power really exist?"
He considered the question for a few moments before turning toward the doll-like young woman standing nearby.
"What missions has Captain Aizen been assigned recently?"
"Individual division deployments are sometimes classified, but the Fifth Division has not undertaken any recent large-scale missions."
Kurotsuchi Nemu answered evenly.
"Then perhaps he really did stumble across some strange record and came here out of curiosity."
Mayuri muttered to himself.
A moment later, he dismissed the entire matter.
He had too many projects demanding his attention to waste time chasing something that might not even exist.
…
Aizen returned to the Fifth Division.
"Captain!"
Hinamori Momo hurried toward him the moment she saw him.
"Captain, the Captain-Commander was looking for you. Where did you go?"
"I visited Captain Kurotsuchi to ask about something."
Aizen smiled gently.
"But the Captain-Commander was looking for me? Did he say why?"
Hinamori lowered her head slightly under Aizen's smile, unable to meet his eyes for long.
"I don't know. But you should probably go quickly."
"Of course."
Aizen nodded pleasantly and turned away.
His expression remained unchanged as he walked, but inwardly, confusion had begun to grow.
And for some reason, he had a strong feeling that the summons might be related to Hueco Mundo.
By the time Aizen arrived, several other captains were already present.
"Captain Aizen."
The others greeted him as he entered.
Aizen returned their greetings with a smile, briefly letting his gaze pass over Third Division Captain Ichimaru Gin before finding a place to stand.
Second Division Captain Soi Fon.
Fourth Division Captain Unohana Retsu.
Sixth Division Captain Kuchiki Byakuya.
Third Division Captain Ichimaru Gin.
And now Aizen himself.
Five captains in total.
Footsteps soon approached.
Apparently, the Captain-Commander had been informed the moment Aizen arrived, because Yamamoto Genryūsai Shigekuni entered almost immediately afterward.
All five captains rose.
Yamamoto looked over them once before speaking directly.
"Something has happened in Hueco Mundo."
Aizen's attention sharpened immediately, though nothing changed on his face.
"A vast forest has suddenly appeared there. Its area is considerable, and many high-level Hollows active throughout Hueco Mundo have begun gathering toward it."
Yamamoto's voice remained stern.
"We need to determine how that forest appeared."
'A forest?'
Unohana looked toward him.
"If this is only an investigation, surely there's no need to gather so many captains."
"This is not merely reconnaissance."
Yamamoto answered.
"You will form an expeditionary unit, determine what has happened there, and if the situation poses a threat, eliminate it."
Gin's eyes remained narrowed in his usual smile.
"So who exactly will be going?"
"There is more."
Yamamoto's expression grew heavier.
"Hueco Mundo has become increasingly unstable over the past several days. According to our observations, large numbers of Hollows are converging on that region."
"You all understand what can happen when that many Menos gather together."
The captains naturally did.
Menos consuming and fighting one another could eventually produce higher-class Hollows—creatures powerful enough that even a captain had to take seriously.
"Soi Fon."
Yamamoto turned toward the Second Division captain.
"You will formulate the operation plan. Share all relevant intelligence with the others."
Having issued his orders, the Captain-Commander turned and left.
Soi Fon rose immediately.
Her expression cold and professional, she began briefing the other captains on everything they currently knew.