Hōzuki Castle had a long and shadowed history.
Back when the Land of Grass still held considerable sway among the minor nations, it was entrusted by others to construct a maximum-security shinobi prison—Hōzuki Castle, ominously dubbed the "Blood Prison."
As time passed and the Land of Grass declined, becoming a fragile buffer between stronger nations, the prison remained. Isolated on a remote island in the sea between the Land of Earth and the Land of Lightning, it was administratively still under Kusagakure's jurisdiction, but it had largely become its own dark domain.
For a shinobi like Kimimaro, the sea was no obstacle.
He and Karin stood on a jagged reef near the island.
"Looks like a Hōzuki fruit tree," Kimimaro observed.
"They say it's edible," Karin said. "But sour."
"Let's take some seeds back. The Land of Vegetables has excellent soil—it'll grow well there."
They looked more like casual travelers than infiltrators. The crashing waves posed no threat to them.
"According to the intel Taketori Takemoto gave us," Kimimaro said, "Mui—the warden of Hōzuki Castle—rarely leaves. The Kusagakure elders visit from time to time. Apparently, they're performing experiments to open the Box of Ultimate Bliss. For that, Mui even sacrificed his own son, Muku."
Karin frowned. "So, what's the plan?"
"You're staying here. I'll deal with Mui."
"You want me to wait out here? Isn't that risky?"
"Hōzuki Castle's Katon: Tenrō no Jutsu—the Celestial Prison Technique—is troublesome. I could defend you, but if I plan to speak with Mui rather than kill him, I can't let you become a bargaining chip. He may still be useful."
Karin understood. "But it's not safe here either. The waves are strong."
"I'll make you a shelter. Wood Release can handle it."
"If the boat is too small, it'll capsize. If it's too large, we'll be spotted." Karin folded her arms. "I'll come ashore, but I'll hide myself."
Kimimaro nodded, and placed a seed in her palm—grown instantly from his Wood Release.
"This seed is linked to me. I can sense your chakra through it. If you're ever in danger, I'll know."
"If you're that worried, maybe I should swallow it."
"It won't sprout inside you," he assured her. "It'll pass through harmlessly."
Karin turned away with a huff. "Little fairies don't poop!" But she obediently swallowed it.
Once on the island, Karin concealed herself. Kimimaro headed alone toward the ominous fortress.
The key was Mui's state of mind.
From Takemoto's reports, Kimimaro had pieced together a portrait of a man broken by grief. Once a noble idealist who sought the revival of the Grass ninja, Mui had become consumed by the legend of the Box of Ultimate Bliss. His obsession drove him to sacrifice Muku—his only son.
Kimimaro's own knowledge of the canon added another layer.
"In the original timeline," he thought, "Naruto infiltrated the prison. Mui used Naruto's chakra to open the Box, hoping to revive Muku—but it unleashed a monstrous entity instead. Naruto was nearly killed before being saved by a priestess with Ryūmei Tensei—Dragon Life Reincarnation."
Even if his recollection wasn't perfect, the important parts aligned.
"The problem," Kimimaro mused, "is that Mui thinks the Box grants life—but it really just revives what's already inside. And I… want that monster's life force. But if it appears too early, it'll be wasted. I can't absorb it all in one go."
His absorption limit had risen to 150,000 units of life energy—sufficient for most jōnin. But the entities sealed in the Box of Ultimate Bliss were in a different league.
"Shippuden-era movie villains always push Kage-level at a minimum. That monster must have life energy in the several hundreds of thousands."
And unlike a tailed beast, it wouldn't patiently wait while he drained it over days.
That's why this wasn't the time for battle—but for diplomacy.
Mujin, the Kusagakure envoy who'd attacked him earlier, had been dispatched by Mui—but they hadn't met face-to-face. With Mujin now dead, there was no blood grudge—yet.
Unless Mui provoked a conflict, Kimimaro had no interest in turning a potential asset into an enemy.
After all, unlike Naruto, Kimimaro was no lone wanderer. He openly ruled one nation and covertly influenced others.
In such matters, strength wasn't the only currency—strategy was.
At Hōzuki Castle, he moved past the outer guards like mist, his chakra cloaked and steps silent. Reaching the office atop the central keep, he knocked lightly.
"Come in," said a voice.
He opened the door.
Inside, Mui sat at his desk, poring over scrolls and sealing formulae. His eyes flicked up—then widened, pupils shrinking.
"Who are you?"
Kimimaro stepped inside. The door slowly shut behind him.
"You don't recognize me?"
"I don't need to. Whoever dares trespass on Hōzuki Castle grounds must be prepared to face the consequences."
Kimimaro's expression remained calm. "So Mujin died for nothing."
Mui narrowed his eyes and rose from his seat. "Kaguya Kimimaro… You dare return here after killing my subordinate? Then don't blame me for what happens next! Fire Release: Heavenly Prison Flame Sword!"
A searing blade of flame burst forth from Mui's palm, shaped by the chakra-forged shackles of the Heavenly Prison technique, and lunged toward Kimimaro.
But before it could connect, a dense orb of water surged in front of Kimimaro, dousing the flames in a hiss of steam.
"No wonder you managed to kill Mujin… You can use Water Release?" Mui muttered warily.
Kimimaro's voice was quiet but firm. "Lord Mui. I did not come here to fight. You sent Mujin to capture me. I eliminated him. That should have been the end of it. But instead, you provoked Iwagakure, didn't you? And if not for the intervention of several senior Kusagakure officials, this castle might already be rubble. I'm offering you a chance to step back."
Mui stiffened. The memory of the rogue Iwagakure bomber still burned in his mind—if not for Kusagakure's intervention, the fallout would have been disastrous.
Suppressing his fury, he asked, "And if I still seek revenge?"
Kimimaro's gaze sharpened. "Then I will bury Hōzuki Castle beneath the bones of its own foundation."
As he spoke, the ground split open and a forest of white bone erupted around Mui—Dead Bone Pulse. Bone spears stopped just short of piercing his throat.
"Make no mistake, Mui. If I wanted you dead, you wouldn't have seen it coming. Think carefully before answering."
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