The underground base.
As the dim golden Flowlight dissipated, Nanatsuki felt an intense hollowness surge through his spiritual body.
The Flowlight he had just used was a fusion of three high-powered sword techniques—Raikiri, Crimson Tide, and Windchase—unleashed together as one.
It was undeniably powerful; Miyamoto Tetsuya hadn't even had the chance to regenerate before being instantly killed.
But the spiritual pressure consumption was equally immense. Ever since his reiatsu had reached captain-class, it had been a long time since Nanatsuki had felt this kind of emptiness from overexerting it.
And the side effects of this technique weren't limited to just spiritual pressure loss.
His entire left arm had gone numb—so numb, in fact, that he couldn't even feel pain anymore.
He glanced at his left hand. The flesh on his index and middle fingers had been completely carbonized and peeled off, leaving exposed bone visible in the air.
Aside from those two fingers, the forearm below the elbow was charred black as well.
The power of Wind-Forged Thunderflame was simply too much—injury during the charging phase had been unavoidable.
Fortunately, Miyamoto Tetsuya had already been slain by the Flowlight. Otherwise, he would've had to retreat into the shadows, rely on Reiatsu-Converging Pills, and fight a prolonged war of attrition—controlling the shadows until he wore the man down.
Nanatsuki took out a pill and swallowed it, gradually recovering his depleted spirit.
As his reiatsu replenished slightly, his Kaido Self-Regeneration ability activated, and a soft healing glow appeared on his blackened left arm.
While his left arm could be recovered using Kaido, the lost flesh on his two fingers would require more than just healing spells.
He'd need to prepare some special reagents back home to regrow the tissue.
Nanatsuki then noticed an update on his status interface:
[Wind-Forged Thunderflame: Blade Sealing (Extreme) – You have fully internalized the sword techniques you've learned, forging your own path.]
He had realized early on that skill points rewarded by the system capped out at "Mastery" level—anything beyond that wouldn't increase further.
Except for the "Culinary Sage" tag that granted Extreme-level culinary bonuses, this was the only technique he had ever elevated to the Extreme tier.
And Wind-Forged Thunderflame: Blade Sealing wasn't limited to Flowlight alone—other techniques like Senmai-Oroshi or Shunpo Iaido could be executed with the same blade-sealing method.
Whoosh—Shihoin Yoruichi appeared beside him in a flash step. Just as she was about to ask about the beam of Flowlight, she saw the state of Nanatsuki's left hand and gasped in shock.
"Sensei! Your hand?!"
"It's just a minor injury. Nothing serious," Nanatsuki replied gently.
"Let me help you bandage it!" Yoruichi, thinking her teacher couldn't dress the wound with one hand, hurriedly pulled bandages from her tactical pouch.
"No need. The outer layer is already carbonized. It won't bleed," Nanatsuki shook his head lightly.
Bandaging was pointless for such a wound—it needed Kaido.
"But it's so bad..." Yoruichi stared at the bones poking out from his fingers, concern flooding her eyes.
"No need to worry. I'm already treating it. The missing flesh will grow back," Nanatsuki said, patting her head with his functioning right hand to reassure her.
"As long as it heals..." Yoruichi nodded, trusting her teacher's Kaido expertise. "But was Miyamoto Tetsuya really that strong? Enough to hurt you this badly?"
"Miyamoto Tetsuya modified his own body. His regeneration is extreme. In this environment, it's nearly impossible to kill him with conventional methods," Nanatsuki paused. "The damage was actually caused by my own technique."
"The move you used—was that Flowlight?" Yoruichi asked. As Nanatsuki's disciple, she recognized that faint golden beam from earlier.
That powerful beam contained razor-sharp killing intent. Among all Katori-ryu sword techniques, only Flowlight could strike from that distance.
"It was Flowlight. Good to know you still remember your training," Nanatsuki chuckled. "That version combined Raikiri, Crimson Tide, and Windchase into one."
"Three techniques in one?!" Yoruichi gasped. "That's insane. I haven't even mastered Raikiri: Flowlight yet."
Her version of Flowlight was still clumsy. She couldn't yet pull off Raikiri: Flowlight, but she could use her Zanpakutō's power to compensate—releasing lightning to mimic the effect.
"That's what you get for slacking on sword practice." Nanatsuki reached out and flicked her forehead. "Feeling jealous now?"
Ever since she learned Shunko, Yoruichi had favored hand-to-hand combat.
She leaned toward melee and didn't often use long-range attacks like Flowlight.
Holding her head, Yoruichi pouted. "I didn't know Flowlight was that powerful..."
"You don't have to use long-range often, but you can't afford to not have it," Nanatsuki smiled. "Still, combining Raikiri: Flowlight with Raibyō's lightning works well too. The Shunko system has potential. You're not on the wrong path."
Yoruichi nodded eagerly. "I feel like I'm close to fusing Raibyō's lightning with a Shunko: Raikiri form! My burst and speed will level up again!"
Raibyō's lightning surpassed standard Kidō-based electricity. The fusion would significantly boost her Shunko state's speed and explosive power.
Just then, her Denreishinki buzzed.
She opened the device and found a message from two Onmitsukidō Shinigami stationed at the surface:
"Vice-Captain! Emergency on the surface!"
"A Gate of Hell has appeared!"
Yoruichi's heart skipped a beat. From what she'd learned, Miyamoto Tetsuya was definitely connected to Hell. A Gate of Hell appearing now was anything but good.
"A Gate of Hell?" Nanatsuki immediately sensed the state of the Sound of Hell—and sure enough, it had detected nearby Hell Reishi.
"Keep monitoring the gate. I'm on my way!" Yoruichi spoke into the Denreishinki.
"We can exit through there," Nanatsuki pointed to the hole carved by Flowlight—it led directly to the surface.
The two swiftly ascended and reached the surface. There, they saw it—a massive door floating in the air, flanked by giant skeletal remains on both sides.
The Gate of Hell was open, radiating an aura of discomfort and dread.
"It's really open..." Yoruichi whispered, stunned.
"Nanatsuki-sensei! Vice-Captain!" the Onmitsukidō Shinigami guarding the surface flew over.
After witnessing the terrifying Flowlight blast earlier, their fears about the Gate of Hell began to ease.
"The gate took Miyamoto Tetsuya's spiritual particles!" Nanatsuki noticed a stream of Reishi drifting into the gate.
Although Miyamoto had been obliterated, he had reached captain-class strength.
And in this world, captain-class souls don't truly die.
Whether in the World of the Living, Soul Society, or Hueco Mundo, once a captain-level soul perishes, sending their spiritual particles to Hell can cause them to revive there.
"So Miyamoto Tetsuya really was tied to Hell. No one held a Soul Burial Ceremony for him, yet the Gate of Hell still came to collect his spirit," Nanatsuki said.
"Can we stop it?" Yoruichi asked.
"Not unless we can destroy the Reishi itself," Nanatsuki frowned.
He didn't have enough reiatsu left to unleash another high-level Kidō or sword technique to destroy the gate.
And even if he did, the gate would simply reassemble—it was much easier to open one in the World of the Living than in Soul Society.
"It seems Hell's Will has the power to forcibly open gates here... But souls sent into Hell still face limitations. Otherwise, it could've just sent reinforcements to help Miyamoto directly," Nanatsuki speculated.
He hadn't seen any guilty souls dragged in—the gate appeared out of nowhere, confirming Hell's Will could open one unilaterally.
After taking in the spiritual particles, the Gate of Hell slowly faded from sight.
"Good. I was afraid we'd have a horde of demons spilling out," Yoruichi let out a sigh of relief.
In Soul Society, tales of Hell were common, and to someone raised there like Yoruichi, the horrors of Hell's demons were childhood nightmares.
"Miyamoto Tetsuya won't easily recreate this scale of experimentation in Hell. He won't be stirring up trouble anytime soon," Nanatsuki said.
Scientific research needed infrastructure—and Hell was barren.
Strength was the true foundation, and Nanatsuki was confident he'd reach a higher level before Miyamoto could act again.
"You found the archive, right?" Nanatsuki asked.
"We did. They're still sorting it. I'll take you there," Yoruichi nodded.
They returned to the underground lab.
Some Onmitsukidō Shinigami were gathering data, while others guarded the elevator shaft.
The upper floor's Reishi Shells had detected the chaos below, but they could only descend via elevator.
The ones that tried were swiftly subdued or eliminated by elite Onmitsukidō forces.
Nanatsuki followed Yoruichi to the data vault.
"Nanatsuki-sensei! Vice-Captain!" the Shinigami greeted him with reverence.
They had initially wondered why a mission like this required bringing Nanatsuki—after all, stealth, assassination, and disguise were their specialty.
Now they understood.
If he killed every threat before it could respond, then stealth was basically guaranteed.
Thanks to him, they could now search the lab freely.
"These boxes are the compiled records. Please check for missing pieces," one elite offered a case of documents.
Onmitsukidō members had always been courteous to Nanatsuki—many believed he might marry into the Shihoin clan.
"Much appreciated. Thank you," Nanatsuki smiled and took the files.
Since the data wasn't fully collected yet, there was no rush to leave. With time to spare, Nanatsuki began reading.
Soon, he discovered Miyamoto's true intentions.
Miyamoto had produced hundreds of Reishi Shells, grown from embryo.
They were entirely different from those previously discovered in Soul Society.
He had selected gifted souls from the World of the Living and used them as templates to grow Shinigami shells from scratch.
These shells had no recorded Reishi data!
Even Squad Twelve's detectors couldn't find their spiritual profiles in any database.
That meant these shells could infiltrate Soul Society perfectly undetected.
"Good thing we got this intel early from the Mizutani family... These shells hadn't matured yet. If they had, Seireitei would be in chaos," Nanatsuki thought grimly.
Hundreds of undetectable Reishi Shells loose in Soul Society? Unthinkable.
"It seems Miyamoto only recently mastered the technique to accelerate embryonic spiritual growth," Nanatsuki flipped through the pages, searching for that method.
Eventually, he found it in one of the document crates:
Spiritual Growth Agent... The main ingredient is extracted from a Hollow?!
The revelation jolted him.
Nanatsuki and Aizen had long experimented with combining Hollows and Shinigami shells—but the results were always disastrous mutations.
And yet, Miyamoto's formula used Hollow essence.
"That Hollow source must be here," Nanatsuki thought, spreading his spiritual awareness to locate it.
In a flash, he shunpo'd to the far end of the lab.
There, behind a door shielded by a spiritual barrier.
Unfolding Shadow Space, he slipped through instantly.
Inside was a room about 100 square meters wide.
At the center stood a large glass tank, far bigger than the ones used for normal Reishi Shells.
It was filled with nutrient fluid brimming with spiritual energy, connected by dozens of tubes to the soul floating inside...