One Piece: Start with Zanpakutō

"Teacher Zephyr is the greatest instructor in all of Marine Headquarters. Naturally, you have your reasons."

Rosen shook his head lightly.

Though he did not fully understand why Zephyr had chosen to stop him, he trusted his teacher's judgment without question.

Even after tasting the intoxicating thrill of rapid Haki growth from slaughtering the prisoners of Level Six, he chose to believe in Zephyr — and left the sixth floor without hesitation.

After all, he was still a newcomer who had only recently transmigrated into this world of pirates, newly exposed to the power of Haki, Devil Fruits, physical techniques, and all manner of abilities.

His understanding of these forces, and how best to refine and elevate them, could not possibly compare to Zephyr — a former Admiral who had once taught three future Admirals.

"Tch, enough with the flattery."

Zephyr scolded him with a smile, yet a trace of satisfaction still flickered in his gaze. The next moment, he shifted into strict-instructor mode, voice turning cold and solemn:

"The reason I brought you to Impel Down was to forge you into a man who can stand at the apex of this ocean. Your Haki, your physical skills, your fruit mastery — every aspect of your being must reach the peak."

"Thus, whether it be battle or training, these are merely means, not ends."

"You must learn to see yourself clearly, to see this world clearly, through each fight against those prisoners. You must temper every facet of yourself, rather than blindly pursue a single attribute's growth."

Hearing this, Rosen's mind churned, deep in thought.

"If I had allowed you to immediately start a second battle," Zephyr continued, "what would you have gained?"

"Perhaps a surge in your Haki?"

"Indeed, with your monstrous talent, you might gain much. But it would still not be enough."

Zephyr's voice turned sharp as a blade:

"What I want is for you to undergo a complete transformation after each fight — not just a mere boost in Haki."

"Such a feat… Borsalino cannot achieve it. Sakazuki cannot achieve it. Kuzan cannot achieve it. Even Garp and Sengoku cannot achieve it."

"But you — Rosen — a man with a talent surpassing every marine legend before you… you can."

His words rang out like a war drum, filled with hope and fierce expectation.

"A complete transformation each time…"

Rosen's mind replayed the scene of his battle with Brynndi World.

What did he lack?

No… it wasn't simply a lack. He had to use World as a mirror, to uncover every weakness in himself, then shatter and rebuild.

"Is it… speed?"

In that instant, he recalled World's terrifying 100-fold amplified speed — the most fearsome part of that fruit.

If not for his superior Observation Haki, that battle might not have been so one-sided.

As Zephyr had said, it was World himself who limited the upper potential of the More-More Fruit.

In truth, that fruit was undoubtedly a top-tier Paramecia, on par with the Float-Float Fruit and the Tremor-Tremor Fruit.

Even if he won, Rosen had to admit — when it came to pure speed, he was still unable to catch up to World.

In their duel, he had been forced into passive defense, unable to seize the initiative.

"Yes, it's speed."

"Even with World's mediocre physical prowess, that 100-fold enhancement allowed him to easily surpass the speed of sound, and perhaps even exceed several times the speed of sound."

"I do not expect you to be faster than a 100-times-boosted World, but…"

Zephyr's voice cut like a blade. "You must at least possess the means to face speed-type monsters without being shackled by your own lack of speed."

At that, Zephyr turned his gaze toward Borsalino.

"Do not forget."

"There exist men in this sea who are faster than World at 100 times their power."

"Do you think your slow, outdated Shave can catch Borsalino's speed of light?"

Hearing this, Rosen subconsciously turned toward Borsalino.

"Teacher Zephyr, isn't this too harsh?"

"At light speed… across the entire Grand Line, I alone possess such speed."

"He is not a Pika Pika no Mi user — how can you force your junior to chase the light itself?"

Borsalino felt Zephyr's standard was far too severe.

Harsh on him — but even harsher on Rosen.

Demanding that a Arms-Arms Fruit user rival the speed of the More-More Fruit… no, even the Pika Pika no mi? Utter madness.

Zephyr's expression remained stony.

"Before I retired, I once fought Kaido."

"He neither possessed the More-More Fruit, nor the Pika Pika no Mi. Yet when he erupted with all his power, his speed was so overwhelming that even my Future vision Observation Haki could not fully evade him."

"And Roger — that man possessed no fruit at all. Yet he suppressed nearly all the kings of the sea, save for Whitebeard."

Zephyr's voice grew heavier, each word like a hammer blow.

"Rosen."

"In the future, your opponents will not be mere pirates like World. They will be monsters — Kaido. Whitebeard."

"With the speed you showed today, even if you multiplied your Haki tenfold, you would not so much as graze their sleeves."

Rosen fell silent, deeply pondering.

Indeed.

Red-Haired Shanks could place a blade at Borsalino's neck — though aided by Future vision Observation Haki, without overwhelming speed, any prediction would be meaningless.

Even Whitebeard, who appeared slow and heavy, was once a monster who could leap across kilometers in his prime.

"How… How can I raise my speed?"

"Shave is merely a physical technique that acts upon the body. Even if I increased my physical strength tenfold, I could never catch up to World with Shave alone."

"But…"

"What if there existed a footwork technique that operated on Haki, rather than just the flesh?"

Rosen's thoughts raced like lightning.

Whether Kaido or Shanks, their monstrous speed was never achieved through mere muscle — it was fueled by that supreme force said to transcend all: Haki.

Shave was fundamentally a technique of the body, not of Haki.

"What if I infused Haki into Shave, so that instead of relying on muscle alone, it was Haki propelling me forward… what sort of speed would that produce?"

Flashes of inspiration burst forth in his mind like meteors.

Rosen's consciousness sank into his inner world of Haki. Even as he observed, he continued to think.

He had already sensed it — this outdated version of Shave could no longer keep up with him.

But that was no obstacle.

If it no longer sufficed — he would create one that did.

"Teacher Zephyr."

"You, Garp, and Sengoku must have long since upgraded Shave yourselves, correct? Melding it with Haki to achieve greater speed?"

"Why not just pass this Haki-version Shave on to your junior?"

Seeing Rosen deep in contemplation, Borsalino leaned over and whispered to Zephyr.

"It is not that I will not teach him," Zephyr replied solemnly. "It is that I refuse to confine his talent."

"From the moment Rosen instantly grasped the Three Forms of Haki, all the Rokushiki, and innovated the Blut Vene and Blut Arterie… I knew."

"This child is a once-in-history uncarved jade. He can be polished — but he must carve himself."

"If I were to carve him, at best he'd become flawless jade. But if Rosen sculpts himself… he will become transcendent."

Zephyr's eyes glowed with a deep, unyielding faith.

… 

[You possess extraordinary comprehension. Through your ultimate foundation and Zephyr's guidance, you have comprehended your exclusive skill · Hirenkyaku.]

[Hirenkyaku: By utilizing Ultra Instinct-level control, you finely condense Armament Haki beneath your feet, then explosively release it to instantly shift your body to another location. The more powerful the Haki, the greater the speed.]

[(Requires Ultra Instinct and Armament Haki.)]

… 

At that moment…

A shimmering line of information blossomed in Rosen's mind like a lotus blooming in the abyss.

...

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