Naruto: Kurotsuchi Mayuri

"You want to control me?"

Kakuzu, a shinobi who had lived for decades, surviving from Konoha's First Hokage's era to the Third Hokage's reign, was naturally wary.

Needing you to replace my heart? Wouldn't that mean I'll always owe you my life?

"You're not just insulting my skill; you're also questioning my integrity," Kagetsu said, narrowing his eyes. "This is a technical issue, not an attempt to control you."

"Is there really a difference?" Kakuzu countered. Trust was not in his vocabulary, neither in people nor in anything—except money.

"The difference lies in this: your inability to replace your heart freely is a technical problem," Kagetsu explained. "And technical problems can be improved and upgraded over time. Once the issue is resolved, the flaw will naturally be eliminated."

"Do you really have such good intentions?" Kakuzu's face was full of distrust.

"I pursue advancements in technology and immerse myself in research. You pursue strength and are consumed by wealth. Can't we each get what we want? If I need you to do something, I'll pay you for it," Kagetsu replied bluntly.

"Payment is acceptable," Kakuzu's heart inexplicably eased. Looking at Kagetsu's youthful face, he found it slightly less annoying. "I'll give you a higher priority."

"Since you prefer a straightforward transactional relationship, Mr. Kakuzu, that makes things much easier," Kagetsu said with a clap, handing Kakuzu a stack of papers with visible delight.

"What's this?" Kakuzu asked, baffled, as he accepted the hefty stack and began flipping through it.

Just a few pages in, Kakuzu's expression began to change drastically. The more he read, the more pronounced the changes became. Within moments, his breathing was heavy, resembling the sound of bellows.

"Your surgery and modification fees," Kagetsu said in a cheerful tone, clearly enjoying Kakuzu's reaction.

"This has nothing to do with me!" Kakuzu stood abruptly, trying to banish the dizzying numbers from his mind.

"Defaulting on debts is bad behavior," Kagetsu remarked calmly, watching Kakuzu. "And, more importantly, your current modifications are incomplete. Without follow-up services, even maintaining your work as a bounty hunter will be difficult."

Kakuzu had half a mind to teach Kagetsu a lesson, but a dangerous aura locking onto him from behind quickly put that thought to rest.

"I'll pay it back," Kakuzu muttered softly. What he was truly thinking, however, was anyone's guess.

"You can also work it off, deducting the amount from the rewards of the tasks you complete for me. No need for actual payment—how does that sound?" Kagetsu asked, watching Kakuzu's emotionless face. He could tell the man was likely scheming something, but he didn't mind at all.

Kakuzu nodded.

"The deal is done," Kagetsu said with a satisfied smile. "The Earth Grudge Fear Masks in your body should have calmed down by now. Can you control it with your consciousness?"

"If so, then try out your new power."

Hearing Kagetsu's words, Kakuzu easily guided the unfamiliar energy within him and began using it.

He felt his body suddenly become much tougher, almost like when he used Earth Release techniques to enhance his defense in the past.

But this time, it felt easier—there were no hand signs needed.

"What is this?" Kakuzu looked at his hands, sensing the energy coursing through his body.

"A Kekkei Genkai," Kagetsu said, then added, "Steel Release!"

Even though Kakuzu had already guessed it, hearing it confirmed left him in a daze.

"The so-called Kekkei Genkai combines two chakra natures in a single individual, allowing them to manifest simultaneously. When this happens, the two chakra natures transform into a new elemental property," Kagetsu explained. "This is the shinobi world's understanding of Kekkei Genkai."

Kagetsu's voice pulled Kakuzu out of his daze.

Compound ninjutsu refers to combining techniques from two elemental natures, either through clones or by using them at different times.

This is fundamentally different from Kekkei Genkai.

"Did this guy really succeed?"

Kakuzu stared at Kagetsu, his mind a whirlwind of disbelief. He had always believed that his mastery over Earth Grudge Fear was absolute, so much so that even the technique's creator couldn't surpass his understanding of it.

Yet, the man in front of him, Kagetsu, had exceeded his expectations. Without knowing the complete workings of Earth Grudge Fear, he had used just the tendrils inside Kakuzu's body to perform an upgrade that Kakuzu himself found unbelievable.

And it worked!

Could it be that Earth Grudge Fear had hidden potential Kakuzu hadn't discovered?

The thought briefly surfaced in Kakuzu's mind but was quickly dismissed by his rationality.

"No!"

Even though Kakuzu had only recently regained his mobility, he could still feel changes in his Earth Grudge Fear. After all, this technique was deeply integrated with him—every minor fluctuation was almost impossible to miss when he focused on sensing it.

It wasn't that the technique's potential had yet to be fully uncovered.

It was that its potential had been artificially expanded!

What was even more terrifying was what he had just heard: the current state of Earth Grudge Fear was still incomplete. There was even more room for it to evolve!

"At present, Earth Grudge Fear can only support two Kekkei Genkai. Steel Release has already taken one slot, so you can choose the second one yourself. Of course," Kagetsu added with a sly smile, "it'll cost you."

Before Kakuzu could voice his choice, Kagetsu continued, "Of course, everything is still in its early stages. There aren't many Kekkei Genkai that are ready for immediate use.

"For now, after you've adapted to Steel Release, the only options available for transplantation are Lava Release, Wood Release, and Blaze Release."

"Wood Release?" Kakuzu's voice was filled with disbelief. Did he just hear a name that sent a shiver down his spine?

"You're interested in Wood Release?" Kagetsu glanced at him, unsurprised by his reaction. Wood Release had been mythologized in the shinobi world for far too long.

"You're saying you can transplant Wood Release into me?" For a moment, Kakuzu began to think that being captured by this kid for experimentation might not be the worst thing to happen to him.

If he could get Wood Release, why would he even need five different hearts with varying chakra natures?

"Don't get your hopes up. It's not going to be on the same level as the First Hokage's Wood Release," Kagetsu said, immediately crushing Kakuzu's expectations. 

"Even if you get a heart with Wood Release, you'll only be able to use basic Wood Release techniques. The First Hokage was an exception."

Even if the Technology Development Department had access to cells from the First Hokage, their current method of using Yin Release to stabilize them would still require an Eternal Mangekyō Sharingan for further research—and where could Kagetsu possibly find one?

Kakuzu still looked reluctant to give up.

"Once it's perfected, and you can handle a third Kekkei Genkai heart, you can pick Wood Release then," Kagetsu offered, trying to appease him.

****

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