Tsunade's heart trembled.
For a fleeting moment, as she looked at Naruto standing before her—his eyes burning with determination—she felt as though she were staring into the past. The overlapping shadows of two people she had once cherished deeply seemed to flicker within him.
Nawaki.
Dan.
The same reckless courage. The same refusal to back down.
"Cough… cough…"
She turned slightly, masking the emotion that briefly surfaced within her.
"I didn't expect you to be this stubborn…" she muttered, regaining her usual composure. "Fine. If you're that determined… I'll help you."
Naruto's face instantly lit up.
"Really?! Thank you, Grandma Tsunade!"
A vein popped on Tsunade's forehead.
"…What did you just call me?"
Naruto froze for half a second—but only half.
"Uh… Hokage-sama?"
"…That's better."
A pause.
Then Naruto grinned again.
"Thanks, Grandma Tsunade!"
"…You brat."
Tsunade sighed deeply, rubbing her temples. There was no winning against him. And truthfully… she didn't really want to.
After all, Naruto had been the one to pull her out of her despair.
If anyone deserved her help, it was him.
The Beginning of a Dangerous Path
Tsunade straightened her posture, her tone turning serious.
"Listen carefully, Naruto. What you're asking for isn't ordinary training."
Naruto nodded, immediately attentive.
"You'll be training two things simultaneously," she continued. "First—stimulating cellular activity. Second—learning to control and repair cells using chakra."
Naruto blinked.
"…At the same time?"
"Yes."
Her golden eyes sharpened.
"I'll teach you how to force every cell in your body into activity using chakra… and at the same time, how to repair the damage caused by that stimulation through medical ninjutsu."
Naruto's expression shifted. Even he could sense how dangerous that sounded.
"You'll repeatedly damage your cells… and then heal them."
She paused deliberately.
"Over and over again."
A chill ran down Naruto's spine.
"This continuous cycle will drastically increase your cellular activity. Eventually, you'll gain the ability to control and activate every single cell in your body."
Naruto swallowed.
"…That sounds insane."
Tsunade smirked slightly.
"That's because it is."
The Principle of the Technique
She raised a finger.
"At its core, this is still medical ninjutsu."
Naruto tilted his head.
"Medical ninjutsu… can do that?"
"Of course."
Her tone was calm—but firm.
"Damaging cells and healing them are fundamentally the same process—just applied differently. It all depends on how you use your chakra."
She gestured lightly.
"Take the Chakra Scalpel, for example. It can save lives… or take them."
Naruto nodded slowly. That made sense.
"This technique…" Tsunade continued, "…is called the Yin Seal."
Naruto repeated it quietly.
"The Yin Seal…"
Shock and Doubt
Beside them, Shizune's eyes widened.
"Lady Tsunade… are you really going to teach him that? That's an S-rank medical ninjutsu!"
Tsunade smiled faintly.
"It's not as unreasonable as you think."
She glanced at Naruto.
"The Yin Seal is deeply connected to the Uzumaki Clan. While it's categorized as medical ninjutsu… it's also a form of sealing technique."
Naruto perked up.
"Sealing techniques? I've practiced those with Jiraiya!"
Tsunade nodded.
"Exactly. That gives you an advantage."
But her expression soon turned serious again.
"Even so… this is still an S-rank technique. Even a prodigy would need one to two years to fully master it."
Naruto's smile didn't fade.
"I don't have that kind of time."
Tsunade raised an eyebrow.
"…Then you'd better prepare yourself."
The Three Techniques
As training began, Tsunade explained further.
"The Yin Seal, Creation Rebirth, and the Strength of a Hundred Seal… are actually three separate techniques."
Naruto listened carefully.
"The Yin Seal is the foundation."
She pointed to her forehead.
"It stores chakra that you accumulate daily into a seal. That chakra can later be released in an instant."
Naruto's eyes widened.
"So it's like… saving chakra for later?"
"Exactly."
"But more than that," she added, "even when inactive, the Yin Seal subtly regulates your body. It enhances cellular control and stability."
She smirked faintly.
"That's one reason I maintain my appearance."
Naruto stared.
"…You're saying that's why you look young?"
Tsunade ignored him.
"Creation Rebirth," she continued, "is the release of that stored chakra."
Her tone grew heavier.
"It forces rapid cell division, allowing instant regeneration."
Naruto's expression changed.
"That sounds amazing!"
"It is," Tsunade said flatly. "But it comes at a cost."
She looked him straight in the eye.
"It shortens your lifespan."
Naruto went silent.
"And the final technique—the Strength of a Hundred Seal…"
Tsunade paused briefly.
"…is still incomplete."
Naruto blinked in surprise.
"Even you haven't finished it?"
She gave a small, confident smile.
"Not yet."
"It spreads the power of the Yin Seal throughout the entire body, constantly maintaining peak condition and allowing immense bursts of power."
Naruto clenched his fists.
"…That's incredible."
"It is," Tsunade admitted. "But it consumes enormous amounts of chakra—even for minor injuries."
Naruto's Resolve
"For now," she said firmly, "you'll focus only on the foundation."
Naruto nodded.
"The Yin Seal."
Even as a "foundation," it was still an S-rank technique—borderline forbidden.
From that day forward, Naruto began training under Tsunade.
Although he had some experience with sealing techniques, medical ninjutsu was completely new territory.
The Challenge of Precision
"Naruto," Tsunade explained during training, "the principle of the Yin Seal is simple."
Naruto listened closely.
"You must guide chakra out of every cell… and then return it to every cell."
Naruto frowned.
"…That doesn't sound simple."
Tsunade smirked.
"It requires extremely precise chakra control."
She folded her arms.
"Even with your sealing skills, mastering this will take at least one or two years."
Naruto crossed his arms.
"…I'll do it in one or two months."
Silence.
Then—
"…What?"
Tsunade's expression darkened instantly.
"Are you looking down on my ninjutsu?!"
Naruto flinched.
"No! Not at all!"
"…Then don't say ridiculous things."
Naruto scratched his head.
"I just… don't have time."
Tsunade snorted.
"I don't care."
Then, suddenly—
"If you can master it in two months…"
She lifted the crystal necklace around her neck.
"…I'll give you this."
Naruto blinked.
"…A necklace?"
He looked unimpressed.
"Why would I want that?"
Shizune gasped.
"Naruto! That's the First Hokage's necklace!"
She leaned closer and whispered urgently.
"It's worth enough to buy several mountains!"
Naruto's eyes widened instantly.
"…Wait, seriously?!"
His entire attitude flipped.
"Alright. I'm in."
The Bet
Tsunade smirked.
"And if you fail?"
Naruto paused.
"…I've got about fifteen million ryo saved up."
Shizune nearly fainted.
"Fifteen million?!"
Naruto grinned.
"If I lose, it's all yours."
Tsunade's smile turned dangerous.
"You're confident."
Naruto shrugged.
"I just won't lose."
Parallel Training
While Naruto trained under Tsunade, the rest of Team 7 was also pushing themselves to the limit.
Hinata focused on strengthening her physical power.
Meanwhile, Jiraiya trained Sasuke.
To counter the Mangekyō Sharingan, Jiraiya developed specialized methods—and also made use of Orochimaru's "gift."
The Cursed Seal.
Though dangerous, Sasuke craved power too deeply to reject it.
Jiraiya added another layer of protection—a Four Symbols Seal.
This ensured that Sasuke could only release the Cursed Seal's full power in desperate situations.
Otherwise, it remained suppressed.
Even so, Sasuke's training was brutal.
Mastering the Heavenly Cover Formation, controlling the seal, and harnessing the cursed power—
Any one of these would be difficult.
Together?
It was hell.
But Sasuke endured.
Naruto's Struggle
Back at the training ground—
"Yin Seal!"
Naruto formed hand signs, focusing intensely.
He began extracting chakra from every cell in his body.
Then—
Slowly—
He guided it toward his forehead.
The principle was simple.
The execution was not.
Naruto had to control over 130 trillion cells.
Each one.
Individually.
The difficulty was like separating droplets of water from a vast ocean—and compressing them into a single point.
Even with his talent…
Even with his sealing knowledge…
It was overwhelming.
Progress… and Pain
Within seven days, Naruto had already grasped the technique's formula.
But understanding wasn't mastery.
Not even close.
Despite his relentless effort—
He had only managed to seal 1% of his chakra.
Just one percent.
Naruto collapsed onto the ground, gasping for air.
His face was pale.
His entire body trembled.
Every cell ached.
It felt as if his entire body had been crushed from within.
"…Still… just one percent…"
His voice was hoarse.
"At this rate… even two years won't be enough…"
Tsunade's Thoughts
From a distance, Tsunade watched silently.
There was a hint of concern in her eyes.
…but also satisfaction.
"Hmph."
"Serves him right for underestimating me."
Yet deep down, she knew something she hadn't told him.
Naruto's chakra reserves were monstrous.
Far beyond ordinary.
If he succeeded—
If he truly mastered the Yin Seal—
Then the power he could unleash…
Would be unimaginable.
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