It was common knowledge: traveling from the Human World to Soul Society wasn't only possible via Senkaimon. There was another route—through the Dangai, the precipice world.
Every time a Soul Reaper performed a konso, guiding a soul to Soul Society, it was fundamentally the act of leading them through the Dangai.
Why was it called the "Precipice World"?
Because within it, everything—space, time, reality—was severed from all known realms.
Not just spatial separation. Temporal as well.
Time inside the Dangai flowed at an utterly different rate.
Scientifically, the overlapping of disconnected dimensions compressed time into a dense whirlpool.
In practical terms?
Two thousand days in the Dangai passed as one single day outside.
This warped flow made it a death trap. Any being with spiritual pressure was distorted by the pressure spiral.
In simple words: leave an ordinary Soul Reaper inside too long, and either body or soul—or both—would suffer permanent, irreversible damage.
Higashi Shuuichi had once entered it.
Stayed under thirty minutes.
Which, by outside time?
Not even a full second.
The higher your spiritual pressure, the worse the impact.
So any idea of using the Dangai for time-dilated training, like a certain protagonist had, was a pipe dream.
That was the hard truth—some people were born to trample rules.
Others spent their whole lives patching holes in them.
Still, it opened Shuuichi's eyes to something else:
This might explain why souls, when crossing into Soul Society, underwent transformation—from ghost to reishi-body.
He realized: this was the key to mastering Fullbring as a Soul Reaper.
Soul modification was just a side effect.
Reverse-engineer the process, and Shuuichi believed he could shift between human and Soul Reaper forms freely.
But to pull that off?
He needed a Soul Reaper who could survive in the Dangai without being torn apart.
To his knowledge, there were only three candidates:
1. Aizen Sōsuke, post-Hōgyoku fusion. Not an option—yet.
2. Kurosaki Ichigo. The destined messiah, Royal Heir, walking contradiction. Also unavailable.
3. Yoshima Ōshu.
An obscure figure in canon, Ōshu had one unique edge:
His Shikai granted limited spatial control.
Using it, he could carve out a pocket realm inside the Dangai.
A domain immune to the time spiral.
In essence: the perks, none of the cost.
The only problem?
Lifespan.
Shuuichi never thought he'd worry about a Soul Reaper's lifespan.
They lived centuries, even millennia. Most never died of old age—battle claimed nearly all.
The Central 46 handed out sentences in hundreds of years like candy.
But with the Dangai's time dilation…
Shuuichi feared Ōshu might train himself past his prime.
He imposed limits.
Ōshu could go in—but not too long. Never too long.
This time was no different.
Ōshu was deep inside, following Shuuichi's structured plan.
His Shikai was already tactically potent—no rush to Bankai.
Instead, he refined his reiatsu, hammered in high-level kidō, all while mastering non-incantation casting to maintain full power during use.
And the Dangai?
He loved it.
Hundreds of bonus years inside a personal training sanctuary.
Sometimes, he felt like the protagonist of a power fantasy.
Outside, not even seven years had passed.
But inside, he'd gained centuries.
He'd surpassed Mayuri Kurotsuchi in pure reiatsu.
Shuuichi's next goal for him was to reach Kyōraku Shunsui's level.
But Ōshu's personal goal?
Higashi Shuuichi himself.
He knew—after Shuuichi absorbed Barragan's Hollow Core, his spiritual pressure edged past Kyōraku.
So Ōshu wanted to surprise him.
Release his reiatsu in full—see the shock on Shuuichi's face.
He couldn't wait.
Despite the temporal bubble, Ōshu and Mayuri had long since developed a compact realtime clock synced to Soul Society.
Seeing the exam time approach, Ōshu prepared to exit.
Then he noticed… something.
A figure.
In the eternal dark of the Dangai, shadows were common.
Souls passed through all the time, led by Shinigami.
But this presence?
Had reiatsu. Strong.
Stronger than most Captains.
On par with Kyōraku.
Ōshu's first thought: Another Captain?
But no—he knew them all.
With Shuuichi and Mayuri backing him, Ōshu had connections everywhere.
There was no one like this in the current Gotei 13.
Which meant…
Interesting.
Two choices:
Stick to the plan. Leave. Go to the exam.
Satisfy his curiosity. Just a peek.
Ōshu chose Option Two.
This was his home turf.
The Dangai was more his backyard than battlefield.
Whoever this was, he had to know.
He approached.
Then blinked.
An old man. Gaunt, skeletal. Skin clung to bones like parchment over wire.
His ribs stuck out.
Ōshu emerged from his pocket dimension and called out.
"Hey. Who the hell are you? What're you doing in the Dangai?"
He was being polite.
But the old man?
Just sighed.
"Tsk. And here I thought I'd sneak into Soul Society quietly. Didn't realize you've got patrols even in the Dangai now."
As he spoke, his hand moved—lightning-fast.
He drew a Zanpakutō that looked like an ancient wooden blade.
And the pressure it released—
Tore open Ōshu's dimensional pocket instantly.
Reishi tide crashed down like a tsunami.
Ōshu gasped, knees nearly buckling.
"13th Division, First Generation—Captain Sakazane Gyakukotsu. Reporting."
His voice was old iron wrapped in contempt.
"F-First Generation… Captain…?"
Ōshu stared, stunned.
Impossible.
The textbooks were clear: most of the original Captains had died in the Quincy war.
This couldn't be one of them.
And yet…
The spiritual pressure. The aura.
It fit.
"Kid," the old man sneered, "your reiatsu's not bad. Way above average. But where's your haori? Don't tell me someone like you isn't a Captain?"
Ōshu scoffed.
"Captain? Who wants that? I'm set to succeed Lord Shuuichi as the next Chief of the Blade-Hunters!"
He steadied his breathing, activating his Zanpakutō again, reforming a protective domain.
The old man… stood unaffected.
The Dangai's pressure didn't even touch him.
That… was disturbing.
"Shuuichi? Blade-Hunters? What the hell are those?
I don't care. I've got one question. Answer it.
Is Yamamoto Genryūsai Shigekuni still Captain-Commander?"
Ōshu hesitated.
"Why do you care?"
Not that he expected a straight answer.
Gyakukotsu had murder in his eyes.
Ōshu knew this wasn't some senile relic.
He was hostile.
But instead of attacking—
Ōshu prepared to escape.
Classic Shuuichi lesson: "No need to die for a system that doesn't give a damn about you."
Ōshu lived by it.
But Gyakukotsu wasn't having it.
"Trying to warn them, huh?
Dream on."
He assumed Ōshu was loyal. Wanted to alert Yamamoto.
Which meant—
Ōshu had to die.
"Quiver in despair—Jigokunaki!"
His Zanpakutō morphed—
From wood to pale bone, deathly aura spilling outward.
Even his hands became skeletal.
Jigokunaki: Grievous Bones.
He stabbed it into the void.
All around Ōshu, reishi waterfalls crashed inward, sealing him in a suffocating cell.
The reishi wasn't ordinary—it reeked of death.
Touching it meant annihilation.
This fight?
Unavoidable.
Ōshu sighed.
"I wasn't planning to fight… but if you insist…"
He steadied himself.
Even if he lost, he wouldn't go down pathetic.
After all, he was Shuuichi-sama's disciple.
And that meant…
He didn't fight for Soul Society.
He fought for himself.
And he never lost without a hell of a show.