(T/N: Sorry guys for not updating as frequently as usual, from now on, it will be 2 chapters a day! Enjoy!)
In the days that followed, Nanatsuki's life was both structured and full.
He shuttled between the Technology Development Bureau and the Sakkise Ore Vein Laboratory.
Training in Quincy abilities had also been added to his daily regimen, and he practiced diligently without interruption.
And just like that—
Twenty years passed in the blink of an eye.
Laboratory.
"Sensei, the Reishi Shell of Shishō is showing signs of Hollowfication again."
Hoshino Rie gave the reminder.
In the cultivation chamber, the Reishi Shell had grown bony protrusions.
"I know."
Nanatsuki frowned slightly.
The soul-growth agents obtained from Miyamoto Tetsuya's lab were essentially extracts from half-human, half-Hollow organisms.
When used to cultivate a Reishi Shell, they inevitably caused the accumulation of Hollow Reishi within the body.
After reaching lieutenant-class, the Reishi Shell of Katori Batsu'unsai had begun to accumulate excessive Hollow energy, making the Hollowfication process inevitable.
In these twenty years, Nanatsuki had produced several captain-class Reishi Shells—every single one of them had undergone Hollowfication without exception.
"Increase the dosage of the high-grade anesthetic sixfold," Nanatsuki ordered. "Don't let it wake up."
"Understood!"
Hoshino Rie nodded and adjusted the controls, raising the anesthetic dosage.
"Looks like we still have to rely on the Hollowfication vaccine..."
Nanatsuki left the cultivation lab and made his way to Aizen Sōsuke's laboratory.
Thanks to Nanatsuki's involvement and access to an abundance of Soul King fragments, Aizen's research had progressed much faster.
Recently, Aizen had developed a vaccine that could temporarily suppress Hollowfication.
"Perfect timing, Sensei," Aizen said, standing beside a surgical table. "I'm running a clinical trial for the Hollowfication vaccine. Please lend me a hand."
Having Nanatsuki—a Kaidō expert—assist would make the procedure much smoother.
"Is that the Reishi Shell of Miyanō Matsuri?"
Nanatsuki glanced at the humanoid body on another table. Most of it was covered in bony plating, but some personal features were still recognizable.
Matsuri had been a Shinigami of Squad Five. Two days earlier, she was gravely wounded by a Quincy while on a mission in the World of the Living.
Her Spiritual Pressure Core had been damaged even more severely than Batsu'unsai's. Aizen accelerated the cultivation of a Hollowfied Reishi Shell using large amounts of soul-growth agents to prepare a core transplant.
"Yes. Matsuri agreed to cooperate with the experiment." Aizen's gaze softened as he looked at her. "Regardless of the result, her contribution won't be in vain. It will give us invaluable data. The Hollowfication vaccine is a promising path, but it comes with its own challenges."
Aizen's charisma was overwhelming. After leading Squad Five for so many years, he had even gained subordinates willing to undergo clinical trials for him voluntarily.
"What's the plan?"
Nanatsuki donned gloves and approached the operating table.
"Let's first replace the Spiritual Pressure Core with the one from the Hollowfied Reishi Shell. Then we'll monitor her vitals before administering the vaccine."
Aizen got to work with the scalpel.
The two of them had performed many operations together. As Aizen exposed Matsuri's damaged Spiritual Pressure Core, Nanatsuki simultaneously extracted the one from the Hollowfied Reishi Shell.
"Hollow Ratio: 53.68%..." Aizen measured the core. "Good—it hasn't exceeded 65%. According to my calculations, once it crosses that threshold, Hollowfication becomes irreversible."
"This core is saturated with Hollow energy. I'd say Hollowfication will begin immediately after transplant." Nanatsuki noted.
"To grow this Reishi Shell in just two days, I used a soul-growth agent dosage sixteen times the normal amount," Aizen explained.
Matsuri's injuries were too severe—she could only survive a few more days. So Aizen had cultivated a Reishi Shell matched to her Spiritual Pressure as quickly as possible.
"Let's begin."
Nanatsuki cut the connections between her core and the Chain of Fate and Soul Sleep.
Aizen immediately handed over the new core.
Nanatsuki moved swiftly, attaching the Hollowfied Spiritual Pressure Core to Matsuri's Chain of Fate and Soul Sleep.
Only after stabilizing the connection did he remove the broken original.
With tweezers, he carefully adjusted the position of the new core to fit precisely where the old one had been.
Once it was in place, Nanatsuki used Kaidō to stimulate the core, Chain of Fate, and Soul Sleep.
Matsuri's core connections activated quickly, and Spiritual Pressure began to flow into the new core.
The Hollow energy inside also began spreading through her body.
"Incredible regeneration..."
Aizen's eyes lit up.
Matsuri's body had begun self-healing!
White matter grew rapidly across the surgical wounds, sealing them in moments.
As expected, immediately after the transplant, Matsuri entered Hollowfication.
"Aaaagh!!!" she suddenly awakened, white matter pouring from her mouth and quickly encasing her face.
"Her Spiritual Pressure is spiking. The original anesthetic dosage can't restrain her anymore."
Aizen monitored the rapidly fluctuating readings.
"Matsuri... can you hear me?"
He tried calling her name, checking for signs of awareness.
Matsuri thrashed violently on the table, snapping the Sakkise restraints on her arms and ankles.
"She's lost her mind."
"Inject the Hollowfication vaccine."
Aizen grabbed the prepped syringe and plunged it into her artery.
The vaccine began to take effect. Her struggles slowed.
After a long while, clarity returned to her blackened eyes.
The bone plating on her body crumbled into dust.
"Matsuri, can you hear me now?"
Aizen repeated gently.
"Vice-Captain Aizen... Captain Katori..."
Matsuri looked at the two of them.
"Do you remember? You're assisting in my experiment. You did well—perfectly, in fact."
Aizen's tone grew even softer.
He had always shown greater patience to those with unique talents.
This wasn't his first Hollowfication vaccine test—
But Matsuri was the first Shinigami to survive the process.
In recent years, Quincy activity in the World of the Living had flared up again—some had even begun actively targeting stationed Shinigami.
Ironically, this gave Aizen more opportunities to test the vaccine.
"I remember."
Matsuri nodded.
"I... I saw another me in the Inner World..."
"Oh? Tell me everything—that's crucial intel."
Aizen said warmly.
"She wore a white Shihakushō. Looked just like me. But her hair, skin... all white. Her personality was nothing like mine..."
"She called herself the embodiment of Hollow energy. Said she would take over my body. I defeated her—and then I woke up."
Matsuri recounted the experience.
"I see... a clash within the Inner World? That means it all came down to your willpower."
Aizen nodded and recorded everything she said.
"You did well. You overcame the Hollow with your own will." He smiled. "Let's run some diagnostics now and see what's changed in your body."
Katori-ryu Dojo courtyard.
A small figure, only slightly taller than a wooden sword, was swinging it with great effort.
"You're swinging too weakly... Did you forget everything I taught you?"
"When swinging a sword, you have to use your back, arms, and wrists together!"
Nanatsuki, who had been casually chatting with Batsu'unsai under the veranda, turned to glance at the training field. He corrected the boy's sloppy form as soon as he noticed it.
Twenty years was a long time for a human.
But to Shinigami, whose lifespans could reach over a thousand years, twenty years meant little.
Two decades had passed, and Kuchiki Byakuya still looked like a child.
The growth rate of a soul body varied between individuals.
Generally, the more gifted one's Reishi aptitude, the longer their childhood and adolescence.
Byakuya had exceptional talent. It had taken nearly thirty years for him to grow from infancy to just above a wooden sword in height.
"Sensei... I've been practicing all morning!" Byakuya panted. "Can I take a break?"
Though still young and not fully mature, Byakuya had begun his training. His father, Kuchiki Sōjun, had asked Nanatsuki to take him as a disciple.
Given his friendship with the Kuchiki clan and Byakuya's potential, Nanatsuki gladly accepted.
"Alright. Rest for now. We'll resume in the afternoon."
Nanatsuki nodded gently.
"Yay!"
Byakuya perked up immediately, then dashed off to the kitchen.
Moments later, he returned with four glasses of chilled orange juice.
"Sensei! Use that bubble Kidō!"
He eagerly placed a cup in front of Nanatsuki.
"You really love fizzy drinks, huh?"
Batsu'unsai chuckled and picked up a cup. She preferred hers without carbonation.
"Orange juice is better with bubbles!"
Byakuya nodded.
A spark flickered at Nanatsuki's fingertip, and the juice began to fizz.
"Sensei, that's amazing!" Byakuya exclaimed. "That Kidō is so hard... Why can't I learn it?!"
He adored carbonated drinks and desperately wanted to master the Kidō that made them fizzy.
Unfortunately, his few attempts had failed.
He had, however, learned the ice-cube-making Kidō. The cubes in the juice were his own work.
"This Kidō requires fine Reiatsu control. You've got a long way to go. Keep training."
Nanatsuki added bubbles to his own glass.
"Aaaah—!" Byakuya took a sip and shivered. "Cold fizzy drinks in summer... unbeatable!"
"Sensei, Shishō, I'm heading out. I'm meeting Miyu at the market!"
Gin Miyu, daughter of the current Squad 6 Vice-Captain Gin Ginjirō, had grown up with Byakuya—they were childhood friends.
"Go ahead. But don't forget sword practice this afternoon."
Nanatsuki glanced toward the gate. He had already sensed Miyu waiting outside.
"Got it!"
Byakuya grabbed two glasses of orange juice and ran out.
"So that's why he brought four glasses. One's for Miyu."
Batsu'unsai sipped her drink with a teasing glint in her eye.
"They're so close... maybe Miyu will be his future wife?"
"Not likely. It's way too early for that."
Nanatsuki shook his head.
Batsu'unsai had guessed wrong. Miyu wouldn't be Byakuya's wife.
No one could've expected that, in the future, Byakuya would fall in love with a woman from Rukongai—crossing the boundaries of nobility.
"You said my Reishi Shell's Spiritual Pressure reached captain-class?"
Batsu'unsai returned to their earlier conversation.
"Yes. But once a shell reaches lieutenant-class, it becomes unstable." Nanatsuki nodded. "Tests show it's due to excessive use of the soul-growth agent. Hollow Reishi builds up over time."
"So... can you replace my Spiritual Pressure Core now?"
Batsu'unsai looked hopeful. She had long been anticipating this moment.
"It's possible—but it comes with the risk of Hollowfication." Nanatsuki explained. "We used the same growth agent when making a shell for Saitō Un. But your strength is greater, and cultivating a captain-class core required even more agent. The core is now saturated with Hollow energy."
"Hollowfication?" she frowned. "You mean I'll turn into a Hollow?"
"Yes. Hollowfication causes Shinigami to lose control and transform." He paused. "But Aizen recently developed a Hollowfication vaccine."
"The vaccine can forcibly suppress the transformation, giving you time to fight back with your own will." Nanatsuki explained. "Whether you succeed depends greatly on your resolve."
The vaccine only temporarily halts the process—it doesn't remove it.
To truly resist Hollowfication, a Shinigami must conquer it from within.
"Any successful cases?" Batsu'unsai asked.
"We tried on Reishi Shells—all failed. They have no awakened consciousness, and even when they do, it's too weak to resist the Hollow energy. So they're not suitable test subjects."
Nanatsuki continued, "But among actual Shinigami, we do have success. Aizen tested it on terminal patients who couldn't be saved by normal means."
"A battle of will, huh..." Batsu'unsai's gaze grew resolute. "I believe in my willpower—I can endure Hollowfication!"
After all, she was Katori Batsu'unsai, the founding captain of Squad Eight!
The original captains had all walked through oceans of blood. Without unshakable will, they would've never made it this far.
She would never fear a challenge!