Kurotsuki Renya hadn't expected the Captain-Commander to doubt him so directly, but he didn't argue or try to force belief. Instead, he straightened and asked calmly,
"Captain-Commander… what must I do for you to trust me?"
Genryūsai Shigekuni Yamamoto looked at him with the same piercing scrutiny that had judged countless Shinigami before him.
"It is simple. You claim Aizen Sōsuke lives, hidden behind illusion. Then restrain him. Expose him. Question him."
Renya frowned sharply.
"That is impossible as things stand. Everyone in Seireitei is still under the complete hypnosis of Kyōka Suigetsu. You cannot even see Aizen's true form. And his power…"
He hesitated.
"…is on a level where, outside of you and Urahara Kisuke, no one stands a chance. If the Gotei 13 attempts to apprehend him head-on, the entire force will be annihilated."
Yamamoto's beard bristled as he exhaled a low growl.
"Are you looking down on the Gotei 13, boy?"
Renya inhaled deeply, forcing his tone to remain respectful.
"I am stating the truth. You have not faced the real Aizen. His strength now is far beyond what he displayed as a captain."
Aizen only cared about two opponents: Yamamoto Genryūsai and Urahara Kisuke. Beyond them, no other Shinigami held his attention. He could defeat most captains in an instant, with or without his Zanpakutō's abilities. Renya knew that too well.
Yamamoto folded his arms.
"Your claims involve matters of great consequence. You have interacted with the captains of one hundred and one years ago. What if Urahara Kisuke is truly the manipulator behind it all? What if the Visored captains participate knowingly?"
He considered the possibility deeply.
If Urahara had disguised Aizen's corpse…
If Urahara had manipulated the Hollowfication incident…
If the Visored and their subordinates joined him…
Then following Renya could compromise Seireitei's greatest defense—Yamamoto himself.
Renya clenched his jaw, aware of how easily suspicion could shift.
Unohana Retsu spoke suddenly, her voice calm but pointed.
"You claimed you possess power sufficient to fight Aizen. Even that your explosive output could match him at his current level."
Renya hesitated.
"Only in short bursts. But yes… at full release, my peak output can reach Aizen's level. For a fight."
Yamamoto's eyes narrowed.
"If that is true, then your strength approaches my own. In which case, combined with Urahara, the former captains of the Visored, their lieutenants, and Yoruichi Shihōin…"
His voice deepened.
"You would possess enough force to assault Seireitei itself."
The Visored contained four former captains, three former lieutenants, and a former Kidō Corps Lieutenant.
Urahara was a former captain and one of the greatest Kidō users alive.
Yoruichi was once Commander of the Onmitsukidō, the Flash Goddess.
Hachigen Ushōda could use high-level forbidden Kidō.
And if Renya could rival Yamamoto in raw output—even briefly—then the entire Gotei 13 as it existed now would be overpowered.
Zaraki Kenpachi's seal remained intact.
Unohana was forbidden to release her true strength.
Byakuya's reiatsu had not yet reached his later evolution.
Renji had not yet attained captain-class power.
The analysis was logical.
Yamamoto raised his staff.
"Therefore, if your words are true, you must possess sufficient strength to confront Aizen yourself. Show it. Here and now."
Renya frowned.
"If I release my spiritual pressure here, Aizen will sense it instantly."
Yamamoto turned toward the corridor.
"Then we fight in Muken."
Muken.
The eighth underground prison.
A sealed abyss beneath the First Division barracks where no reiatsu could escape.
The same prison where Aizen would one day be confined, and where Unohana and Zaraki would clash in the future.
Inside Muken, Aizen could not sense anything—not even Kyōka Suigetsu could reach that deep.
"Will you verify your strength?"
Yamamoto's gaze sharpened. If Renya refused, the Captain-Commander would restrain him immediately.
But Renya smiled faintly.
"Of course. I want to test my strength as well. I haven't had an opponent capable of drawing out my full power."
In the Human World, he had sparred with the Visored.
Kensei's power equaled Renya's blurred-state Baida.
Love and Rose could be overwhelmed with his dual-blur configuration.
Shinji could be neutralized with EMP-type attacks.
None of them forced him to fight seriously.
He looked forward to facing the Captain-Commander.
"Good."
Yamamoto struck the floor with his staff. A moment later, a figure entered.
It was First Division Lieutenant Sasakibe Chōjirō.
"Sōtaichō, what do you require?"
"Prepare the passage to Muken. Clear the area. No one is to see where we go."
Though doubt remained, Yamamoto did not discount Renya's warnings entirely. To avoid Aizen sensing anything, their movements had to remain hidden.
Chōjirō left immediately to perform the task. Moments later he returned, saluted, and withdrew.
Then Yamamoto led Unohana and Renya through the corridors toward the lowest prison.
Muken lay deep beneath the First Division compound, below seven higher underground prisons that held the most dangerous criminals in Soul Society.
And Muken—the eighth prison—was the deepest and most isolated place in Seireitei.
They descended through passage after passage, arriving at a heavy iron door.
Yamamoto unlocked it, revealing a long stairway leading into the abyss.
After what felt like an eternity of descent, they reached the final iron gate.
Yamamoto inserted the key.
Rumble…
The gate opened, revealing a vast, silent darkness. A suffocating, oppressive void—like a place where sound itself had died.
"This is Muken."
Yamamoto stepped down into the gloom.
Unohana placed her hand on the doorway.
"I will remain here. Once the door opens again, I will heal whoever needs it."
Renya nodded and handed her his cloak and tools.
"Thank you, Captain Unohana."
He stepped inside.
Unohana closed the massive door behind him.
Darkness swallowed everything. Renya could sense only the immense, ancient reiatsu of Yamamoto standing before him.
"If you cannot defeat me," Yamamoto said, his voice echoing deeply,
"then you remain here."
Renya unsheathed his Zanpakutō.
"Then let's begin, Captain-Commander."