Captain Unohana:
If you are reading this letter, Captain… then I have either been imprisoned or am already dead.
By the time this reaches your hands, the truth may already be buried beneath Aizen Sōsuke's lies. You must read carefully — for this letter reveals the true culprit behind the corruption that has plagued Seireitei for decades.
The one responsible is none other than Captain Aizen Sōsuke of the Fifth Division.
He is not the gentle and refined man he pretends to be. Behind that calm smile lies a Shinigami who, even eighty years ago, had already reached the pinnacle of power — and has long sought to surpass the very limits of the Shinigami race itself.
To achieve this, Aizen has pursued a forbidden breakthrough: the creation of an artificial soul known as the Hōgyoku — a device capable of dissolving the boundary between Shinigami and Hollow, granting one the power to transcend both states.
At the same time, Urahara Kisuke, during his tenure as Twelfth Division Captain and founder of the Shinigami Research and Development Institute, had been developing a similar object.
Seventy-one years ago — or one hundred and one years by official Seireitei records — Aizen used his incomplete Hōgyoku to forcibly Hollowfy several captains and lieutenants during a secret experiment.
He then framed Urahara Kisuke, resulting in his exile, along with Tessai Tsukabishi, the former Chief of Kidō.
Both escaped execution thanks to the intervention of Yoruichi Shihōin, who defected that same night.
The tragedies that followed — including the creation of Metastacia, the Hollow that consumed Kaien Shiba's wife and devoured countless Shinigami — were all orchestrated by Aizen.
The creature that attacked me and the one that took Kaien-dono's life both bore traces of his Reiatsu manipulation.
If I die or am accused falsely, then know that Aizen Sōsuke has moved against me in secret retaliation.
Tōsen Kaname and Ichimaru Gin are his loyal subordinates.
Never trust their words — they act under Aizen's command.
If I am gone, Captain Unohana, I beg you — deliver this letter to Captain-Commander Yamamoto Genryūsai Shigekuni himself.
But before doing so, verify the body they claim to be mine.
Aizen's Zanpakutō, Kyōka Suigetsu, allows him to manipulate perception perfectly. If my corpse appears… ensure it is truly me. If my body cannot be found, or if I am said to have defected — then know that I may still be alive.
If that is the case, wait thirty years. I will return to expose Aizen's treachery myself.
If thirty years pass and I do not return… then my final attempt has failed, and I am already dead.
Aizen's two great ambitions are these:
1. To perfect the Hōgyoku, enabling his evolution beyond the limits of Shinigami and Hollow.
2. To enter the Soul King's Palace, within the Royal Realm, by forging the forbidden Ōken (Royal Key) — a key that can only be created through a massive ritual requiring the sacrifice of an entire district of souls.
He learned of the Soul King's Palace after the former Twelfth Division Captain, Hikifune Kirio, was promoted to the Royal Guard (Zero Division).
Aizen intends to recreate the Ōken through forbidden means, but will not act until he acquires a perfected Hōgyoku — the one that currently resides within Kuchiki Rukia's soul, though he is unaware of it.
When the Central 46 decrees Rukia's execution, using the Sōkyoku at the hill of execution, it will not be for justice — it will be Aizen's ploy to retrieve the Hōgyoku hidden within her.
If that time comes, Captain Unohana, deliver this letter to Captain-Commander Yamamoto.
Prepare an ambush — for it will be Aizen's moment of exposure.
Now, regarding his Zanpakutō: Kyōka Suigetsu (Mirror Flower, Water Moon).
Its true ability is Complete Hypnosis (Kanzen Saimin).
The illusion does not merely obscure vision — it controls all five senses of the target, making them perceive false reality as truth. Once one has seen Kyōka Suigetsu's release, they remain under its hypnosis permanently.
He can alter perception so completely that no one can tell friend from foe.
Even Captain-Commander Yamamoto and yourself, Captain Unohana, are already under its influence.
The only way to nullify Kyōka Suigetsu's hypnosis is to touch the blade of the Zanpakutō before it is released.
If you plan to strike him down, inform Ichimaru Gin of this method — he will understand what must be done.
Aizen's power is unparalleled. He has achieved Kurohitsugi (Black Coffin) — a Level 90 Hadō — without incantation, and can repel Bankai-level attacks with his bare hands.
Only Captain-Commander Yamamoto, whose flames surpass all others, possesses strength equal to face him directly.
Be cautious, Captain Unohana. The fate of Soul Society may rest upon the knowledge contained in this letter.
– With respect,
Kurotsuki Renya
⸻
Unohana Retsu lowered the letter, her sharp eyes narrowing.
The air around her grew heavy — a chilling aura of murderous intent.
So… the mastermind of the Hollowfication incident seventy-one years ago was Aizen Sōsuke.
Metastacia, Ramirez, every manipulated Hollow — all his doing. And now, Renya's death.
Aizen's outward gentleness, his calm demeanor — all a façade.
Still, Unohana's mind weighed the evidence cautiously.
If Aizen truly commanded both Gin and Tōsen, then why had Tōsen succumbed to Hollowfication?
Had Aizen abandoned him as a failed subject?
The scene during Renya's last mission flashed through her mind — Gin had been present during Tōsen's betrayal. That matched what the letter described.
The letter's final note also implied Gin might turn on Aizen one day, if given the means to destroy Kyōka Suigetsu's hypnosis.
Could it be… Renya foresaw everything?
Unohana folded the letter slowly. Despite the storm of doubt in her heart, she knew what she must do.
Renya's words — written at the cost of his life — could not be ignored.
Even if she was uncertain, she would not act rashly.
The only rightful recipient of this truth was Yamamoto Genryūsai Shigekuni himself.
Aizen's strength, his illusions, his intellect — if this letter was true, then every Captain in Seireitei had already been deceived.
And if Renya was still alive somewhere… he would return when the time was right.
For now, all she could do was wait.
Unohana tucked the letter carefully back into her robes. Just then, Isane Kotetsu's voice came from outside:
"Captain, the Head-Captain requests your presence in the First Division Hall."
"Understood. I'll come immediately."
Unohana rose quietly, the folds of her haori brushing the tatami as she left her quarters and made her way to the First Division barracks.
Inside were Captain-Commander Yamamoto, Kyoraku Shunsui, and Shiba Isshin — the latter called in as a senior advisor.
Unohana bowed.
"You called for me, Captain-Commander?"
Yamamoto nodded gravely.
"Yes. Captain Tōsen of the Ninth Division has fallen in battle after his attempted betrayal. Captain Suì-Fēng struck the fatal blow. The Ninth Division is now without leadership."
He continued, his tone heavy but resolute.
"Captain Ukitake has recommended Shiba Kaien for the vacant captaincy. Following protocol, I have summoned the three senior captains — Kyōraku Shunsui, Aizen Sōsuke, and yourself — to evaluate his worthiness."
Unohana nodded in acknowledgment.
Traditionally, the assessment of a new Captain required a nomination, confirmation by the Head-Captain, and review by three senior Captains of standing.
Normally, those would have been Unohana Retsu, Kyoraku Shunsui, and Ukitake Jūshirō — but since Ukitake was Kaien's sponsor, he was excluded. In his place, Shiba Isshin, the head of the Shiba branch family, had been called.
Isshin smiled faintly.
"No objections here, old man. But I'd like to see the kid's power myself."
Yamamoto nodded.
"You may."
Kyōraku chuckled.
"He was already Vice-Captain eighty years ago, when Tōsen was still a seated officer. With his potential, it's no surprise."
Unohana folded her hands, calm as ever.
"Shiba Kaien… he has both strength and character. Has he achieved Bankai?"
Yamamoto gave a single, firm nod.
"Enter."
The doors opened. Shiba Kaien stepped into the hall, straight-backed and solemn. He bowed deeply.
"Captain-Commander. Captains."
Isshin's expression hardened slightly.
"Kaien… are you ready for this responsibility?"
Kaien nodded, eyes unwavering.
"Yes. I am."
Yamamoto's eyes glowed with quiet approval.
"Then… show us your Bankai."
Kaien drew his Zanpakutō, its blade gleaming under the light, and called its name with a powerful voice—
"Bankai — Nejibana Kōrin!"
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