Laboratory.
Nanatsuki was adjusting the life-support chambers.
A full row of them stood before him, each one filled with nutrient solution.
Inside these pods, Katori Batsu'unsai's Reishi Shells were being cultivated.
After confirming that Saitō Rei's condition was stable, he'd begun cultivating Batsu'unsai's shell next.
Nanatsuki recorded today's data.
"Developing faster than Saitō Rei's shell... is it due to spiritual particle aptitude?"
He had discovered that the Reishi Growth Agent, which accelerated cultivation, didn't produce the same effect on all shells.
Batsu'unsai's shell was developing noticeably faster than Rei's.
"If this pace keeps up, it might take even less time than expected. I estimate one year to reach seated officer-level Reiatsu... and possibly vice-captain level within five years."
In contrast, Rei's shell couldn't hope to reach vice-captain level Reiatsu within five years—even her original self hadn't hit that level yet.
As for how long it would take to nurture Batsu'unsai's Reiatsu to captain-class... even Nanatsuki couldn't say.
Whether this method could truly produce captain-level Reishi Shells remained an open question.
After logging the data, Nanatsuki headed to another chamber—to check on the Hollow Shell Aizen had been cultivating.
He walked through a narrow corridor and arrived at a lab built deeper into the mountain.
This lab was constructed with a much higher ceiling than the others.
The reason? It had to house a massive Gillian-class Menos Grande.
This towering creature wasn't naturally formed.
It was a Hollow Shell.
The result of Aizen's latest research.
"Sosuke, didn't you have to attend the Shin'o Academy True Blade Trials today? Why are you back so soon?" Nanatsuki spotted Aizen inspecting the Gillian's vitals.
"The group stage wasn't that competitive—it ended pretty early," Aizen replied while jotting notes.
This was their first time successfully cultivating a Gillian-class Hollow Shell, and Aizen was extremely cautious. He'd returned immediately after his match to monitor it personally.
"You guys all passed, right?" Nanatsuki asked with a smile.
He'd been too busy tuning Batsu'unsai's shell the past few days to watch the matches himself.
As vice dean now, he no longer had to serve as a referee like the other teachers.
"Sōya didn't pass..." Aizen explained. "He was in a group with Lisa and Komamura. The competition was tough."
"All three of them in the same group? Yeah, that's brutal..." Nanatsuki frowned. "But as long as you make the top three in your group, you should still be eligible to challenge another group's winner, right?"
He had personally set that rule—to provide some margin for error.
The group assignments for registered natural-born students had been arranged randomly by the other instructors.
"There was another strong fighter in that group—Iba Tetsuzaemon," Aizen added. "Neither Lisa nor Sōya could beat him."
"Iba... that should be the son of Squad 3's vice-captain, right?" Nanatsuki recalled.
"Then Sōya must've lost to Lisa and missed the challenge round," he said, shaking his head. "That kid never trains properly. Now even Lisa's surpassed him!"
Lisa had been born in Rukongai, while Sōya came from a much better background. In the beginning, Sōya had been stronger.
"Well, maybe it's a good thing he didn't advance. Let this loss be a lesson."
Nanatsuki turned back to the Gillian. "So, how's this one doing?"
"The Reiatsu spike has ended. It's in a stable phase now—should be fine," Aizen replied, a faint smile on his face.
This was a major breakthrough for their shell experiments—they'd never successfully created a Gillian-level Hollow Shell before.
"Triggering its predatory instincts... what a clever idea," Nanatsuki remarked.
While Nanatsuki had been away in the Dangai, Aizen had noticed a limit in the development of their Hollow Shells—they stopped growing past a certain point.
That's when he thought about how Hollows evolved into Menos Grandes in Hueco Mundo.
Aside from the naturally born Gillians, most Hollows in Hueco Mundo evolved through cannibalizing their own kind.
So he tried it—activating the predatory instinct in one Hollow Shell and letting it devour the others.
These already-powerful shells cannibalized each other and soon produced a Gillian-class Hollow Shell.
"Hollows evolve the same way in Hueco Mundo," Aizen said. "Following this path, we may be able to produce Adjuchas-class ones too."
"Then keep going. Once we have one at the Adjuchas level, we'll use it for the Shinigamification Experiment." Nanatsuki nodded.
"Shinigamification experiment, huh..." Aizen paused his data recording.
"I tested that concept on a few Hollow Shells recently, but still got nothing."
He let out a soft sigh. "I don't think it's a matter of how strong the Reiatsu is. Even if we use an Adjuchas-level Gillian, the result may be the same. Injecting Shinigami Reiatsu alone just doesn't work."
Aizen had tried forcing Shinigami Reiatsu into Hollow Shells to trigger Shinigamification—but every attempt had failed.
"I don't think it's that simple," Nanatsuki said. "This time, we're adding something else."
He pulled out a long, thin bone fragment.
About one or two centimeters long, its shape and size instantly drew Aizen's attention. With his extensive dissection experience, he recognized it immediately—a small segment of leg bone from some unknown being.
But what struck him even more was the strange Reiatsu pulse emanating from it.
Neither Shinigami...
Nor Hollow.
"Wait… is this…?" Aizen's eyes narrowed, recalling some ancient texts he'd seen in the Shiba Clan's archives.
"You guessed right," Nanatsuki nodded. "This is a bone fragment from the Soul King."
The power contained within it was unmistakable—Soul King's power.
Nanatsuki had found the fragment deep within the Forest of Menos, then divided it into three parts. This was one of them.
Aizen's breath quickened. After reading the secret archives of the Shiba Clan, he'd been tempted to obtain a Soul King fragment for research.
He never imagined his teacher had already secured one.
"Sensei… please let me study it!" Aizen's thirst for knowledge surged.
"I brought it out just for you," Nanatsuki smiled.
Aizen looked as if he'd just received a priceless treasure. His instincts told him that the key to both Hollow Shinigamification and Shinigami Hollowfication lay within these fragments.
Later that night...
By the time Nanatsuki returned to the Katori-ryu Dojo, it was already late.
When he reached his room, he found someone curled up fast asleep at the doorstep.
Nanatsuki crouched down and gently turned her over.
"Mm... Sensei, you're back?" Lisa rubbed her sleepy eyes.
"Lisa?" Nanatsuki blinked. "Why are you sleeping out here? Why not in your room?"
"Ah!" Lisa suddenly remembered why she was there and snapped awake. "Sensei! Please guide me in Zanpakutō Meditation Training!"
"It's already so late…" Nanatsuki chuckled. "Why not wait until tomorrow? I can make time then."
"But the quarterfinals will be full of opponents who've already unlocked Shikai… I want to awaken mine before the matches!" Lisa grabbed his sleeve, pleading. "I don't want to lose in the top eight. Sensei, please~!"
She knew her teacher had been extremely busy lately—and might not have much time even tomorrow. So she'd waited up, hoping to catch him tonight.
"…Fine, fine. Come in," Nanatsuki finally gave in, heart softening when she started to beg.
With his spiritual body's resilience, he didn't actually need to sleep unless severely injured. Sleeping was a leftover habit to feel human.
Seeing how much his student wanted to grow, he didn't mind skipping rest.
Once inside, Lisa glanced around curiously. She rarely entered her teacher's room and found everything fascinating.
It was clean and tidy, except for a vase beside the desk, filled with wilted flowers.
"These are already dead..."
"Been there a few months," Nanatsuki scratched his cheek. He'd been too busy to change them.
"Then I'll replace them for you next time!" Lisa's eyes lit up. She already found an excuse to come again for more lessons.
"Mm. Sit down," Nanatsuki said, lighting a censer and motioning for her to sit across from him.
Soon, gentle smoke wafted through the air, filling the room with a calming fragrance that settled the mind.
"Sensei, I'm ready!" Lisa sat cross-legged and placed her Asauchi across her lap, entering a meditative pose.
She'd undergone Zanpakutō Meditation Training before and was familiar with the process.
"I'm coming in, then." Nanatsuki sat across from her, placing his hand atop her Zanpakutō.
Tapping into his experience, he immediately entered deep meditation.
In the blink of an eye, Nanatsuki found himself inside a chaotic inner realm.
This was Lisa's Inner World.
It hadn't yet fully formed—her inner world was still in an unstable, transitional state.
Normally, if an Inner World hadn't solidified, a Shinigami wouldn't be able to access it on their own through meditation.
But with a teacher's guidance, Lisa could enter early.
As Lisa's consciousness arrived, she immediately sensed the presence of another being—
Her Zanpakutō spirit.
She focused, trying to connect with it.
Within the Inner World, communication with the spirit was far more efficient than in the outside world.
Nanatsuki watched as the chaotic world gradually took shape.
"Water?" He noticed large amounts of water forming and pooling together.
Not just water—earth and gravel emerged too.
They began to merge, forming a large pit.
Water from earlier flowed into the pit, slowly filling it.
"A lake? No... more like a large pond," Nanatsuki observed. It wasn't big enough to be called a lake.
After the pond formed, the world began changing rapidly—like watching a video in fast-forward.
The environment developed around it.
Bridges, pavilions, drooping leaves—all took shape around the pond.
The transformation continued, expanding the world outward.
The pond now sat like a piece of jade embedded in the earth—serene and deep.
Soon, a mist veiled the water like a sheer curtain. It looked like a realm from a dream.
Sunlight filtered through the haze, glinting across the surface.
Green trees lined the shore, and willows swayed gently.
It was so beautiful, Nanatsuki could almost smell fresh earth and grass.
Of course, as a consciousness body, he couldn't actually smell anything.
"What a beautiful Inner World," he praised.
It was far more elegant than his own desert-like world.
Just then, a black-tailed dragonfly emerged from the pond and landed on his shoulder.
Nanatsuki immediately recognized it—it was Lisa's Zanpakutō spirit.
The dragonfly emitted a warm, familiar presence.
Thanks to the structured meditation, Lisa's Inner World had formed faster, improving the spirit's environment as well.
"You still don't want to tell her your name?" Nanatsuki asked as he picked up the spirit's intention.
"Not yet," the dragonfly responded.
"Why not?" he asked. "Lisa's talent and resolve are both top-tier. I think she'll be an excellent Shinigami."
"She is," the dragonfly agreed. "But if I give it up too easily, she might not treasure me later."
"So you want to test her?" Nanatsuki raised an eyebrow.
"Exactly. If she passes, I'll tell her my name."
"What kind of test?"
"…Dunno. You decide."
"Me?" Nanatsuki scratched his face.
That was unexpected. He'd never seen a Zanpakutō spirit leave its test to someone else before.
But then again—no one else could enter another person's Inner World like this.
"I trust you," the dragonfly said innocently.
"…Alright. How about... having her learn a new sword technique?" Nanatsuki suggested cautiously.
"Too easy," the dragonfly said flatly. "And she has to learn it before the quarterfinals begin."
"…That's a bit rough," Nanatsuki muttered, scratching his head again. "But fine, we'll do that."
Lisa was still immersed in her silent communication with the spirit.
She had no idea that the dragonfly had already made a deal with Nanatsuki.
If she could master a high-difficulty sword technique before the tournament...
Then she would be told the name of her Zanpakutō.