The underground laboratory was deep and dim, the light flickering hot and cold.
"Another failure, huh."
This was Kurotsuchi Mayuri's first attempt at creating an artificial Shinigami. A rushed experiment could only yield a failed result.
"You're trying to fuse a Gigai (artificial body) and a Gikon (Mod Soul) to create a true Shinigami?"
A voice came from behind him—Higashino Shuuichi.
Mayuri turned and faced the man calmly. "So you saw through it?"
He wanted to face death with poise, yet Higashino seemed in no hurry at all to take his life.
"You're being impatient."
Higashino stepped past him to the ruined workbench, lifted the failed Gigai in both hands.
"This time failed only because I rushed it. If I had more time—"
Hearing Higashino critique him in a field he felt was his own, Mayuri pushed back.
"Do you think I'm talking about this experiment, Mayuri?"
Seeing Mayuri's emotions quietly pried open, Higashino knew the hook had sunk.
Compared to Urahara Kisuke's leak-proof, all-angle defenses, Mayuri was still a step behind.
"Isn't that what you meant?"
Mayuri had already forgotten why Higashino was here. All he wanted now was to know why Higashino would say such things to him.
"Gikon and Gigai are, in the end, things we made. You jumped straight to combining these man-made products to birth true life. The stride is too big. The difficulty between here and there—I'm guessing it's not just 'a little,' is it?"
Higashino held the failed Gigai up between them, letting his words hit harder.
"Then is there a gentler path in between?"
Mayuri heard the implication, but aside from directly fusing Gikon and Gigai, what better method was there?
"You know this, Mayuri—I'm no researcher. But in the World of the Living I learned two words from researchers there: technical accumulation."
"Technical accumulation?"
Seeing Mayuri now thinking at his pace, Higashino smiled. It meant his purpose here was, in all likelihood, secured.
"Yes. The reason it feels impossibly hard isn't that your direction is wrong. It's that you lack most of the techniques needed to realize it. To use a clumsy analogy: you're a baby who hasn't learned to crawl, already daydreaming about running. You might succeed in the end, but the process will be grueling and full of uncertainties."
"A baby who hasn't learned to crawl…" Mayuri thought through his own path.
In truth, his initial impulse to "make a person" was simply the urge to create a new technology Soul Society had never seen—to prove he was second to none, especially not to Urahara Kisuke, who used to overshadow him at every turn.
So yes: when it came to creating a true Shinigami, he was utterly green.
"Vividly put."
Mayuri didn't skimp on praise, then counter-asked, "Since you put it that way, you have a plan, don't you?"
He wasn't a complete social imbecile. If Higashino had already bared the dagger this far and still hadn't struck, it had to be because he wanted something.
"Do you know about the humans in the World of the Living who call themselves Fullbringers?"
Seeing Mayuri had already guessed and yet stayed even-tempered, Higashino felt the stone in his chest settle.
"Fullbringers? I heard of them recently," Mayuri nodded after riffling through his memory.
"Recently?"
This time Higashino was surprised. He'd been ready to explain—after all, for Shinigami who rarely worked topside, Fullbringers would be foreign. Even among Thirteenth Division members who surveilled the World of the Living, those who knew of Fullbringers were few.
But Mayuri had heard—and only recently. That was… interesting.
"The armored warriors you met on B3 were brought from the World of the Living by me—by a human who called himself a Fullbringer."
He paused, then added as if guessing Higashino's next thought,
"Mm—based on orders from the Tsunayashiro clan."
"So the Reigai (artificial spiritual body) technology was also taken from you by the Tsunayashiro clan?"
Higashino pressed.
"Seems you've met those armored warriors up there?"
Mayuri's thoughts flicked to a certain man named Urahara Kisuke. Perhaps only he could have sniffed out the shadow of Reigai tech from those shattered remains.
"That tech was something the Tsunayashiro clan told you to research?" Higashino asked.
Mayuri shook his head. "I only obeyed orders to transfer a portion of archives relating to Reigai tech. As for who received it—you should know him."
"Someone I know?" Higashino frowned.
He knew many Shinigami in Soul Society, but the number who could take over Reigai work and actually advance it could be counted on one hand: Urahara Kisuke, Aizen Sōsuke, Kurotsuchi Mayuri, Yushima Ōko, and one more who'd yet to truly show his hand—Yamada Seinosuke.
The first four could be ruled out outright. Which left… Yamada Seinosuke? That felt far-fetched.
Yes, in the future Yamada would work for the Tsunayashiro—well, for Tokinada Tsunayashiro, since by then he alone remained the face of the clan. But before that—at this point in time—who would have realized that beyond medicine, Yamada Seinosuke had real research chops?
Higashino was ready to accept the unlikely truth—when Mayuri named someone unexpected yet oddly fitting.
"Kapu Holmes, Captain of the Development Team under Soul Society's West Administration. If I'm not mistaken, your file says you fought him in the World of the Living and lost—nearly died by his hand. The space gem you handed me to research seems to have come from that encounter."
"Kapu Holmes, huh?"
Dead memories surged, assailing Higashino.
A name he'd nearly forgotten—and the direct cause of his present situation. Because he'd met that man by accident, and even with his infinite regeneration lost miserably—nearly died—so he resolved to risk contacting Hell ahead of schedule. Which led to a string of deviations never in his original plan.
But if it was that man… and if he stitched Mayuri's offhand details together… a clean web formed in Higashino's mind.
West Administration. Fullbringers. Tsunayashiro clan. And Aizen's earlier speculation.
The Kasumiooji affair had shown the other nobles—especially those still holding the reins among the Five Great Noble Houses—a new picture: that their lofty clans should have forces of their own. Not this current state of bending the knee to Yamamoto Genryūsai Shigekuni, commanding a single division, and even having to obey his deployments.
Clearly, the Tsunayashiro clan wanted to imitate the Kasumiooji and privately raise an armed force loyal only to themselves.
In Soul Society, that was hard. The Kasumiooji had bled for it. So the Tsunayashiro looked instead to the World of the Living—to Fullbringers—leaking sealed contraband tech to the West Administration to strike a deal.
Yet the clearer the line grew, the more one question irked Higashino: as one of the Five Great Houses, the Tsunayashiro couldn't be ignorant of the Fullbringers' native flaws.
First, as humans, Fullbringers had no advantage in lifespan against Shinigami.
Second, because they hold fragments of the Soul King's body within, Fullbringers cannot undergo proper Konsō (Soul Burial) by Shinigami. When they die in the World of the Living, their souls can only drift alone through the Dangai (Precipice World) between worlds. The chance of actually reaching Soul Society is one in ten thousand.
(Author's note within the setting: the CFYOW Kasumiooji/Kūkaku arc and Tsukishima's "ascension" to Soul Society in canon nearly overturn prior Fullbringer rules. Without this restriction, Soul Society ought to be packed with Fullbringers.)
With those two built-in limits, why still raise a Fullbringer army?
Of course, maybe he was overthinking it—maybe the Tsunayashiro had simply reached some other arrangement with the West Administration.
"Back to the point: what do Fullbringers have to do with me making Shinigami?"
Seeing Higashino lost in thought, Mayuri cut in. He clearly didn't want to chase that thread further. Whatever the Tsunayashiro were up to had nothing to do with him. The armored warriors had only excited his hunter's curiosity, and from them he'd teased out a remote-control system.
Hearing the question, Higashino reeled his thoughts back.
If the Tsunayashiro really intended to raise a Fullbringer corps, that would cut across his plan to collect Fullbringers, learn Fullbring, and gather Soul King fragments. But looked at from another angle, it saved him time hunting them down. Poaching targets was faster than searching blind.
"If I'm not wrong, three conditions must be met to birth a Fullbringer. One: the mother carries an unawakened fragment of the Soul King's body. Two: before giving birth, the mother is attacked by a Hollow, leaving Hollow power behind in her body. Three—and most important—while the child is gestating, the Hollow power and Soul King fragment merge into the human soul as it forms. Only when all three are met does a Fullbringer emerge."
"So still no necessary link to making a Shinigami, is there?"
Mayuri understood, but didn't yet see the bridge between Fullbringers and his "manufactured Shinigami."
Higashino smiled. "Viewed straight on, the link looks thin. But Mayuri—what was the reason I had to flee to the World of the Living with Urahara Kisuke?"
He loosed his Reiatsu (spiritual pressure) again—murky, dark, volatile.
"Hollowfication!"
A gray skull mask formed over his face; his clothes shifted to pure white.
"You've mastered Hollow power?!"
Mayuri's mind clicked: that nagging oddness about Higashino—he'd seemed too normal.
"No, Mayuri—others can frame it that way. You, of all people, should care about why I can Hollowfy."
Feeling that savage, different Reiatsu and prompted by Higashino's nudge, Mayuri understood.
"Because a true Shinigami shouldn't contain only Shinigami power and a Shinigami soul—but also Hollow power. Correct?"
"Exactly. Now do you see? You can first work with a Shinigami Reigai, plus a human soul and Hollow power—using the Fullbringer birth as a reference—to research modifications to the soul across these three components."
"And then once that tech matures, I just swap the human soul for a Gikon, and I can realize the manufactured-Shinigami concept by the quickest route."
Higashino didn't need to say more; Mayuri ran the logic and saw the whole chain.
Indeed, if he advanced in the steps Higashino proposed, it would be much faster than sealing himself up to reinvent the wheel. Fullbringers were excellent reference material—and expendable.
After a brief, silent calculus, Mayuri looked at the now-de-masked Higashino, eyes bright with the future.
"Name it. What do you want me to do?"
There was no free lunch—of that he was clear.
Higashino hadn't risked coming from the World of the Living into his den just to lend a hand.
Curiously, though Higashino had all but demolished the lab and offered no "tangible" help beyond a new path, Mayuri felt he owed him a colossal favor.
"Hold that thought."
Higashino signaled him to wait; he wanted to test a hypothesis first.
"Heihō Sogen (Tracing the Origins of Warfare), Bankai! Shakushi Kankon (Borrowed Flesh, Returned Soul)!"
Terrifying Reiatsu surged, then flowed along his Zanpakutō into the failed Gigai before him.
He poured until his Reishi dropped to half.
A new "corpse" took shape.
"So that's how it is…"
Even carrying half of Higashino's Reishi now, the peak Reiatsu this body could vent had barely risen—only to about a Tenth Division–captain level. Higashino got it.
Back when he used Shakushi Kankon to make bodies, he'd noticed: when he used random dead things from Soul Society, the "corpses" had a cap on how much Reishi they could be filled with—and on how much peak Reiatsu they could output.
Using ordinary dead matter, a "corpse" peaked around a basic captain class, and its Reiatsu bled away quickly with battle and Kidō use.
Even now, with a Gigai as the shell, the storage jumped—endurance improved greatly—but the output didn't rise much.
He guessed that as his own Reiatsu climbed, the ceiling of bodies made with Shakushi Kankon would rise slower and slower. What he could increase was mostly their stamina.
Even so, paired with his other Bankai power, the burst he could field was still respectable.
When he first grasped Hyakki Yagyō (Night Parade of One Hundred Demons), he recognized its flaw: to lure the roving oni from Hell to possess, you needed an actual body for them to gnaw. His Reishi constructs were pure Reishi—not "physical" in the usual sense—so he had to use Shakushi Kankon to give them an outer shell so Hyakki Yagyō could run properly.
But bodies made from common dead matter couldn't stand up to Hell's oni chewing for long. And if there was nothing to bite, those Hell fiends would "lie flat" like fed-up wage slaves and scuttle back to Hell.
Pay for pay's worth.
Gigai were different. Like a Shinigami's body, they were… chew-resistant.
"Maybe someday it'll be a true Hyakki Yagyō…"
He pictured it: himself alone above the worlds, a single command, and the sky black with his ghosts. Very cool.
Only problem: those ghosts would likely be small fry.
He withdrew the image, finished the test, and raised three fingers to Mayuri.
"Three terms.
One: we'll be in close contact from here on. You don't need to find Fullbringers—I'll bring them to you. In return, I need you to grease my movements inside Soul Society.
Two: I need you to provide as many Gigai as possible, and the Soul King fragments left in those Fullbringers after you're through with them.
Three: I have a disciple in Soul Society—Yushima Ōko—currently a member of your Twelfth Division. He's got real research talent. I want him in on the project."
"That's all?"
Mayuri listened without much ripple—he even felt he was making out like a bandit.
The first condition—facilitation—was nothing, so long as Higashino didn't trigger major incidents. Given Soul Society's current "cold treatment" toward these fugitive Shinigami, it barely counted.
The second was even easier. Gigai were trivial compared to Reigai; with enough materials, he could make as many as he wished. As for Soul King fragments—interesting, yes—but keeping a small stock for future study was enough. Handing the rest to Higashino was no problem. Before he finished the manufactured-Shinigami plan, he'd have no time to run a massive Soul King-fragment project anyway.
And if someday he did need a lot of fragments? Easy—notify Soul Society and have the captains gang up on Higashino.
So the second demand was basically no demand.
Only the third irked him. He didn't like others' hands in his research—least of all someone who'd aided Urahara in Reigai studies.
Anyone Urahara had used—disgusting.
"But hear me: if Yushima Ōko doesn't satisfy me, I won't keep him, even for your sake."
"Of course."
Higashino was confident. He trusted Yushima's talent—after all, a single split-personality of his had handled soul modification and even mastered the Dangai. With Higashino and Mayuri as mentors, how could the main body lag a stray persona?
They discussed more details—how to bring Fullbringers in, how to meet, and so on.
At last, Mayuri forged him a Gigai identical to his old one; Higashino also "borrowed" a few black-tech trinkets. Then he swaggered out of the lab he'd nearly razed to the ground.
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