Seireitei is vast. The Gotei 13 headquarters, the noble estates, and the central administrative districts all stand within this circular fortress surrounded by walls made from sekki-seki, the infamous spirit-killing stone.
Ordinary souls cannot enter freely—access is only possible through the four great gates: North, South, East, and West.
As for invading Seireitei from above?
That is no simple matter.
The sky itself is layered with the Reishi-repelling barrier membrane, a powerful defensive screen that prevents unauthorized entry.
However, it is not inviolable. There is one family that developed a way to breach it.
The Shiba Clan—once one of the Five Great Noble Houses—possessed a unique technology:
spatial penetration.
In the manga, when Kurosaki Ichigo and the others infiltrated Seireitei to rescue Kuchiki Rukia, they relied on Shiba Kukaku's Tenshintai Cannon to blast through the barrier.
Later, when the Zero Division returned to the Royal Palace, they also used the Shiba family's method to ascend.
Even above Seireitei, the barrier leading to the Royal Realm is far stronger—full seventy-two layers of spiritual defenses—but the Shiba techniques can still break through.
As for Shutara Senjumaru, who lived in Seireitei for many years before ascending to the Royal Guard, reentering Seireitei this time was effortless.
She knew the city's structure intimately.
She helped create many of the organizational systems during her time in the 12th Division, and she never forgot the internal design of Seireitei.
And her power had grown tremendously.
After her promotion to the Zero Division, her bones were reforged through the Spirit King's power, and after adapting to the overwhelming reiryoku density of the Spirit Palace, she had become even stronger.
There are cases where a newly promoted Royal Guard member has not yet fully matured in power, but once one gains the Ōken-infused bone reconstruction and lives within the Spirit King Realm—where reiryoku concentration far exceeds even Hueco Mundo—it is only a matter of time before they become overwhelmingly strong.
For an ordinary vice-captain, entering the Royal Palace would feel suffocating, even lethal.
Shutara Senjumaru quietly slipped into Seireitei, using one of the Zero Division's new concealment arts to hide her presence. She walked through the Court Guard halls like a phantom.
"Compared to that era… not much has changed,"
she murmured.
Though her time in the Royal Guard was not long by Shinigami standards, centuries still passed—enough that she expected to see more progress from Seireitei.
She moved toward the Seireitei Research and Development Institute, formerly the Department of Research in the 12th Division.
This was once her place.
Many of those inside were familiar faces—some were gone, replaced by new recruits, and others she recognized from her time before ascending.
"Kurotsuchi Mayuri… so he finally ended up arrested for being too dangerous."
Senjumaru reflected quietly.
She remembered encountering Mayuri during her tenure. His genius was undeniable, but so was his instability. She taught him certain fundamentals, yet even then she sensed how dangerous his ideas were.
If not restrained, he would inevitably land in the Maggot's Nest.
Today, he was nowhere to be seen—confirming he had indeed been detained.
It was also possible he had committed a greater offense and had been executed, though that was less likely.
After spending some time observing the institute, Shutara Senjumaru proceeded silently toward the captain's room.
Inside, Sarugaki Hiyori, the 12th Division lieutenant, was arguing with Hikifune Kirio. Senjumaru did not interrupt. When Hiyori left, Senjumaru quietly stepped inside.
Hikifune Kirio—long purple curls, warm features, and a naturally voluptuous figure—was preparing to rest when a sudden sensation struck her. She immediately turned toward the disturbance.
Her expression shifted instantly—gentleness replaced by a sharp, formidable presence.
"…It's me."
A woman's voice echoed, and a figure manifested from nothing.
Hikifune blinked in brief surprise.
"Senjumaru? Is that you?"
"Kirio, it's been a long time," Senjumaru replied. In age, she was Kirio's senior, but in position, Hikifune had been her captain during her time in the 12th Division. Regardless, they were old comrades.
"You… shouldn't you be—"
Hikifune did not finish the sentence, but she clearly knew Senjumaru had joined the Zero Division.
"I came for you," Senjumaru stated.
"Oh?"
A flicker of curiosity crossed Hikifune's eyes.
Senjumaru straightened, her tone turning formal as she addressed her by full name:
"Hikifune Kirio. You have created something with profound influence on the Soul Society. Your achievements meet the standards for promotion to the Zero Division."
"On behalf of the Royal Guard, I extend an official invitation.
Will you accept ascension to the Zero Division?"
Hikifune's expression hardened.
She remained silent for a long moment before answering:
"I need time to consider this."
Senjumaru expected that response.
When Kirinji Tenjirō invited her long ago, she had given a similar answer.
She nodded gracefully.
"I hope you can decide soon."
Whether acceptance or refusal, it required a prompt conclusion.
Hikifune nodded, acknowledging it.
Afterward, Shutara Senjumaru stayed within the 12th Division barracks. Though many years had passed, this was once her home, and some of her hidden private spaces remained untouched since no one ever discovered them.
Returning now, she occupied them once more.
Days passed quickly after Senjumaru's return to Seireitei.
Hikifune Kirio still had not made a decision.
Senjumaru, growing restless, found her thoughts drifting toward someone.