Naruto: Reborn as Kakuzu, the Immortal Assassin

In the elegant and spotless Bio-Research Lab No. 2, the scene was tranquil. A cup of strong tea, a pack of cigarettes, and a book on the desk created the perfect setting for a relaxing day. For Kakuzu, earning a daily salary of 20,000 ryo in a stable position within Konoha's system was nothing short of a dream job.

But such serenity rarely lasted in a shinobi's world.

Swish!

Kakuzu furrowed his brow slightly, instantly aware of the disturbance. Without turning around, he knew—Tobirama Senju was back.

The Second Hokage, having wrapped up his previous tasks, was back to his relentless pursuit of forbidden jutsu. For every new forbidden jutsu he created, another would inevitably be banned. Despite Hashirama's numerous admonishments and the fact that most of Tobirama's research had been buried or outlawed, the man's resolve was unshaken. Science, after all, did not wait for anyone's approval.

This time, though, Tobirama had brought something... different.

Kakuzu glanced over his shoulder and saw two individuals sprawled on the ground, breathing shallowly. They had been brought along with Tobirama's signature Flying Thunder God Technique.

"You're getting bold," Kakuzu remarked. The presence of living subjects signaled the start of human experimentation. While Kakuzu was unsurprised, he recalled that Hashirama had explicitly forbidden such unethical studies.

"Relax. They're death-row inmates from Konoha's prison," Tobirama replied, his gaze cold. "They'll contribute to the village one last time—with their lives."

"Well, if anyone can rationalize skirting the rules with such eloquence, it's the champion of the Will of Fire," Kakuzu muttered as he got up, donning white gloves and preparing for work.

Tobirama ignored the jab, stroking the stubble on his chin thoughtfully.

"Oh, by the way, there's something I need your help with."

"What is it?"

"The research funding from the village is tight, and I can't allocate too much to this project without raising suspicion. My resources are running dry. I need you to contribute some funds, or this experiment won't progress."

The room fell silent.

Clang.

The forceps Kakuzu had just picked up dropped to the table. He looked at Tobirama, his expression unreadable.

"If it's that difficult, maybe it's a sign you should abandon the project. Don't expect me to cover for you—I want my salary paid on time."

Tobirama crossed his arms, his haughty expression a mix of irritation and stubbornness.

...

Three Months Later

Two new forbidden jutsu were born.

The first was entirely Tobirama's work, inspired by a genjutsu technique passed down within the Senju Clan. He refined and developed it into what he called the Dark Night Walking Technique. This genjutsu created an all-encompassing darkness that robbed the target of their sight. Only the caster and their allies could navigate the blackened environment, giving them a decisive advantage.

In short, it temporarily stripped the enemy of light itself.

The second jutsu was a collaboration between Tobirama and Kakuzu: the Mutual Multiplying Explosive Tags. This technique focused explosive power on a target, creating a cascade of detonations so devastating that it left nothing behind—not even ash. It was particularly effective against opponents with teleportation, evasion, or resurrection abilities.

The success of these jutsu left Tobirama thoroughly satisfied.

One evening, after months of grueling work, the two finally sat down to enjoy a well-earned drink.

"Tobirama-sensei, Kakuzu-sama, please try this—it's my family's secret recipe for sake," Sarutobi Hiruzen said as he presented the bottle with pride.

"Hm, good boy," Kakuzu said, patting Hiruzen on the head.

Oddly enough, Danzo was absent, which was unusual for someone so eager to curry favor. Perhaps Tobirama had deliberately excluded him. Kakuzu didn't particularly care.

Taking a sip, Kakuzu let out a satisfied hum.

"Not bad, Sarutobi. Bringing this sake to honor your teachers shows you've got your head on straight."

"Thank you, Kakuzu-sama! I'll keep working hard," Hiruzen replied, beaming.

Tobirama gestured for Hiruzen to leave the bottle and clean the inner lab. Once Hiruzen was gone, Kakuzu sipped his sake and casually remarked, "Tobirama, are you planning to start a civil war?"

Tobirama froze mid-drink.

"What are you talking about?"

"Don't tell me you haven't noticed how both of these jutsu seem tailored to counter the Uchiha." Kakuzu's tone was neutral, but his point was razor-sharp. The Dark Night Walking Technique nullified the Sharingan's sight, while the Mutual Multiplying Explosive Tags was devastating enough to counter even techniques like Izanagi.

For a moment, Tobirama closed his eyes, considering his response. He had multiple ways to deflect the accusation. He could deny it outright or attribute it to his experience in countless battles against the Uchiha.

But deep down, Tobirama knew the truth.

Saying something like this in front of Kakuzu was nothing short of inviting ridicule. After a long silence, Tobirama Senju set his sake cup down and finally spoke.

"First, I never underestimate anyone who threatens the village. That includes people like you in the past."

Kakuzu didn't refute this. Even though the two of them were currently working together, he knew well that a shrewd politician like Tobirama would always keep his guard up.

"Second," Tobirama continued, "are you not aware that there is a child in my ANBU team named Uchiha Kagami?"

"Oh? What exactly are you implying?" Kakuzu's voice carried a hint of curiosity, though his eyes remained sharp and calculating.

Tobirama fell silent once again, his gaze drifting to the laboratory window. Kakuzu could sense the faint trace of reminiscence in his expression. After about half a minute, Tobirama spoke again, his tone more reflective.

"The Uchiha clan is one that loves deeply—so deeply that their love can become unbearable. But that depth of emotion isn't something most people can handle."

He paused, then continued, "One wrong step, and that love spirals out of control. I've always been trying to guide that power towards a righteous path, rather than rejecting it outright. That's why, when dealing with the Uchiha, I've worked to open their hearts and integrate them fully into Konohagakure. Kagami is the person I've chosen to lead that effort. Do you understand now?"

Kakuzu nodded slightly, understanding Tobirama's intentions. If possible, Tobirama hoped to see the Uchiha fully assimilated into the village. However, given the Uchiha clan's proud demeanor and their apparent lack of regard for others in Konoha as true comrades, such a goal seemed distant. That pride often bred resentment and heightened mistrust, which, Kakuzu surmised, was likely one of the reasons behind Tobirama's development of certain forbidden jutsu.

Tobirama didn't view the Uchiha as enemies, but neither did he fully trust them. At least for now, he hadn't reached the point of branding them as an "inherently evil clan."

Just as Tobirama and Kakuzu were about to shift the conversation, the sound of rapid footsteps interrupted them.

Whoosh!

A Chūnin darted into the laboratory with urgent speed. Besides Tobirama and Kakuzu, only Tobirama's trusted disciples could enter this space so freely. The newcomer was Danzo, his expression tense and full of unease.

"Tobirama-sensei! There's trouble—it's the Uchiha…!"

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