Naruto: Kakashi, the Ultimate Shinobi

After opening his eye for only a moment, Kakashi promptly shut his Mangekyō Sharingan. Yet in that brief instance, he felt his chakra deplete rapidly, and his mental stamina was drastically drained.

"No wonder the Kakashi from the original timeline collapsed from overuse of the Mangekyō," he muttered quietly. "It wasn't just chakra exhaustion—it was mental fatigue too. The double burden probably pushed his body past its limits."

Kakashi pressed his hand against his temple, fingers brushing his silver hair, a hint of exasperation in his expression. At this stage, using Kamui even once felt like his limit.

Fortunately, this was just the beginning. Once he gained more control and honed his skill, he could potentially increase his usage. As he aged, his chakra reserves and mental resilience would also grow, allowing for more activations over time.

One of the greatest drawbacks of the Mangekyō Sharingan was the inability to train with it extensively. Excessive usage led to a rapid loss of vision. Every use came at a cost, making casual training impractical and even dangerous.

Unless one awakened the Eternal Mangekyō Sharingan or implanted Hashirama's cells, the burden remained irreversible and the cost severe.

Still, with the Mangekyō now awakened, Kakashi finally had a formidable ace up his sleeve. If used unexpectedly, Kamui might even be lethal against a Kage-level foe—he had that much confidence.

The Four Symbols Seal appeared again, re-sealing the Sharingan. His chakra surged back to normal levels, wrapping around his body in a familiar flow. After repeated use, Kakashi had grown highly proficient in managing the seal—activating and suppressing it had become second nature.

Under the cold moonlight, Kakashi drew Chidori Blade, leaped into the courtyard, and began to swing it silently. He didn't channel chakra—just precise, relentless swings. The art of swordsmanship, not ninjutsu, was what he refined tonight.

Upon closer observation, his blade work had subtly shifted from his traditional Hatake style. It now appeared less aggressive and more fluid—still deadly, but adaptable and reactive.

Each swing blurred into the next, creating faint afterimages. The cool night wind howled through the trees, the moon casting silver on steel, painting a lonely but resolute picture.

---

At dawn, Kakashi stood before Guy's home. Coincidentally, Guy was just stepping out, full of enthusiasm.

"Kakashi! Done with your mission? Then let's ignite our youth with a challenge!"

Kakashi gave a rare smile and nodded. He had indeed come to train his taijutsu. And with Guy, a friendly match was the perfect warm-up.

"Yosh! What's our wager today?" Guy asked, eyes blazing with energy.

Since the Nine-Tails attack, Kakashi had stopped brushing off Guy's challenges. He took them seriously now, and it filled Guy with pride.

He didn't know what had caused Kakashi's transformation, but he didn't need to. Even if he tried thinking about it, he likely wouldn't get far anyway.

"Let's head to the training grounds. I've got business afterward," Kakashi said casually.

"Yosh! Let's go!" Guy shouted, dashing toward Training Ground Seven without hesitation. Kakashi followed, half-exasperated by Guy's intensity.

That morning, villagers watched two figures—one clad in black, the other in bright green—blazing through the village streets. The green one laughed maniacally, leading some to mistake him for a madman.

Kakashi instinctively put some distance between them. It was just too embarrassing.

"My eternal rival, Kakashi! I'm going to push my speed!" Guy bellowed, accelerating with a grin.

Kakashi's lips curved up slightly. "Heh. Then I'll just have to keep up."

They arrived simultaneously at the seventh training field.

"Ah, the flame of youth burns bright today! It's a draw!" Guy exclaimed. "Let's settle this with an all-out taijutsu duel!"

Before Kakashi could even blink, Guy launched a punch. Kakashi quickly stepped back, dodging a strike that would've left a bruise.

"Warn me next time, will you?"

"Ha! The enemy won't warn you! And I did say it!"

"Well... you've got me there."

Guy didn't wait for more banter. He followed with a flying kick.

Kakashi had no time for words now—he shifted into combat mode.

"Konoha Whirlwind!"

The heavy strike came slicing toward him. Rather than dodge, Kakashi caught the leg mid-air and pivoted, slamming Guy into the ground with a fluid motion.

"Impressive! You neutralized my Konoha Whirlwind! But now—Konoha Strong Whirlwind!"

Guy twisted in midair, releasing a more powerful spinning kick.

Kakashi's Sharingan flared, and his body flickered.

He vanished.

Guy's kick met empty air.

"Huh? Where'd he—?"

A voice whispered behind him.

"Konoha Taijutsu Secret Technique… A Thousand Years of Death!"

Guy's face turned pale. "W-what kind of forbidden technique is th—?!"

Before he could finish, Kakashi formed the tiger hand sign behind him and—stab!

"AAAHHHH!!"

Guy screamed as he was launched into the air, clutching his rear.

Kakashi chuckled, examining his fingers with a mischievous glint. "Still works like a charm."

Groaning on the ground, Guy rolled over and cried, "Kakashi! What kind of ultimate move is that? I've never seen such a brutal taijutsu secret!"

"It's the Thousand Years of Death."

"Amazing! What a name! Is this your own creation? A true pinnacle of Konoha taijutsu?"

"Yeah… something like that."

"You truly are my eternal rival! Creating your own secret taijutsu—this is youth! I've got to push myself even further!"

Guy's eyes burned with resolve.

"Guy… don't overdo it," Kakashi muttered, scratching his head.

But clearly, Guy had tuned out all distractions, now lost in his fiery world of youthful fervor.