One Piece: Start with Zanpakutō

"Conqueror's Haki?"

Facing the roaring surge of Haki, there wasn't even a flicker of surprise on Rosen's face.

This was Impel Down, after all—where monsters were gathered. It was perfectly normal for there to be pirates who possessed Conqueror's Haki.

"Let's see if we can give it a try."

King against king.

When they meet, there is always a collision of spirit.

This is the greeting of kings, a silent handshake of the strong.

If you can withstand it—then you are worthy of further words.

If you cannot—then there is no need to speak further.

Thinking this, Rosen didn't back down at all. Instead, he poured all his consciousness into his Haki, like a sky-splitting blade surrounded by endless oppressive force, slashing down toward Douglas Bullet's Conqueror's aura.

Boom!

The moment the two Conqueror's Hakis collided, a deafening thunderclap reverberated in every ear throughout Infinite Hell.

Then—

The originally invisible waves of Haki turned into two gigantic torrents—one gold, one purple—colliding fiercely, erupting into a chaotic storm.

Seen from afar—

It was as if two ferocious dragons were locked in mortal combat, biting and clawing at each other.

Every collision of Haki unleashed shockwaves like crashing tsunamis and landslides.

Every clash of spirit split the air with black and red lightning bolts.

Every prisoner felt as if two colossal mountains had appeared from nowhere, crushing their souls, leaving them gasping for breath under an unspeakable, suffocating pressure.

And this conflict was far from over.

Without anyone realizing, at the very top of Impel Down—above the first floor—the sea of clouds began to twist and churn like a giant vortex.

The clash of Conqueror's Haki from the depths of the sixth floor had penetrated rock and sea, surging skyward like an upwelling current, distorting the heavens and stirring whirlpool clouds.

"Being suppressed?"

"As expected!"

"That is the spirit of a devil's descendant! Even though he's been locked away for years and is far from his peak, he is still terrifying beyond measure."

"How could some young, green Marine brat possibly surpass that monster's spirit?"

"Although... he's pretty impressive to even hold out this long."

The prisoners all thought this was a one-sided suppression.

They never imagined that while Rosen's Conqueror's Haki was indeed being pushed back, it didn't collapse. Instead, it stood as firm as a rock, confronting Douglas Bullet's overwhelming might head-on.

"Indeed."

"Technique is technique, intensity is intensity."

"Even though he's been imprisoned for years and is no longer at his peak, Bullet is still Bullet after all."

Rosen felt no surprise or shame at seeing his own Haki suppressed.

Douglas Bullet had been battling on warfields since childhood. After destroying his own country, he joined Roger's crew and fought day after day alongside monsters like Roger, Rayleigh, and others.

Later, even after being beaten down by Garp and Sengoku during the Buster Call and thrown into Impel Down, his foundation had not been shaken.

Meanwhile—

How long has Rosen Practiced Haki?

Three days, at most.

And Douglas Bullet?

Over a decade.

"So this is his spirit?"

In that instant, through the clashing Haki, Douglas Bullet felt Rosen's essence and roughly gauged his level.

To be honest—he felt somewhat disappointed.

This level of Haki had just barely crossed the threshold of mastery into Haki Infusion. It wouldn't give him any surprises.

However—

Just as Douglas Bullet was about to forcibly end the clash, his expression abruptly shifted, revealing an incredulous shock.

Not just him—

Except for Zephyr, everyone else throughout Impel Down was staring at Rosen's aura in utter disbelief.

From initially being absolutely suppressed, Rosen's Haki began to slowly rise, like a giant waking from slumber, step by step pushing Douglas Bullet's force back.

"How is this possible?!"

Shiryu's eyes widened in horror, a roar echoing inside his mind.

"Junior..."

"His spirit is growing stronger... no, he's evolving!"

"But this rate of growth... is too outrageous."

Borsalino turned to stare at Rosen beside him, his face filled with utter astonishment.

Although he did not possess Conqueror's Haki, he understood it deeply.

Why do kings always clash with Haki upon meeting?

Because it is both a deterrent and a greeting—an unspoken duel of spirits.

The collision of Conqueror's Haki, whether by internal entanglement or external burst, is like the forging of steel.

Only by enduring countless collisions and with an unyielding will can one's Haki continue to sharpen and evolve.

But such growth never happens after merely one or two exchanges.

Even if there is improvement, it should be minuscule—not the monstrous, stepwise escalation Rosen was now displaying.

Yes.

It was rising steadily, visibly, step by step.

Under the immense suppression of Douglas Bullet, Rosen's Conqueror's Haki was like a dragon lifting its head, continuously expanding in a completely unreasonable fashion.

"I knew this would happen."

Zephyr stood there with his arms crossed, his face calm—no surprise at all. Instead, there was a deep, knowing smile in his eyes.

He had already noticed this tendency during Rosen's battle with Gion and Tokikake.

Every time Rosen unleashed his Haki—whether Observation, Armament, or Conqueror's—there would always be a tangible improvement.

Moreover, this improvement would only magnify as the opponent's strength and external pressure increased.

Against Gion and Tokikake, he had already advanced significantly.

And now, clashing head-on with a monster like Douglas Bullet, who stood at the pinnacle of the sea, Rosen was bound to see even greater leaps.

This was also why Zephyr insisted on bringing Rosen to Impel Down.

To other Marines, Infinite Hell was truly hell—

But to Rosen, it was a treasure trove of experience, a paradise for leveling up.

"As long as you can't overwhelm him in a single blow, his Haki will skyrocket."

Zephyr watched Rosen's ever-expanding aura, the smile in his eyes growing brighter.

"He's using my Haki... to Cultivate."

Douglas Bullet finally realized.

Back when he sailed with Roger's crew, he had done the same countless times—seeking out Roger, Rayleigh, Jabba, and others to forcibly grow stronger.

But he never imagined that one day, he would become someone else's training dummy—

And worse, that Rosen's improvement from this one clash exceeded the gains Bullet himself had reaped from months of battles with Rayleigh.

"Tch!"

Douglas Bullet's face turned grim as he immediately retracted his Haki, forcibly ending the clash.

After all—using others for experience is exhilarating, but becoming the tool for someone else's growth? 

That's simply intolerable.

Especially at Rosen's absurd growth rate. Another two or three minutes, and Rosen's Haki might even catch up to or surpass his own.

Even though he found this unbelievable—

He did not doubt it at all.

"Why stop so soon?"

Seeing Bullet forcibly end the clash, Rosen looked disappointed, as if he hadn't eaten his fill.

He then glanced at the message that popped up in his mind:

[Your comprehension is extraordinary. Through clashing with Douglas Bullet's Conqueror's Haki, combined with your Haki Core Origin, your Kingly spirit has undergone a breakthrough Evolution.]

[Conqueror's Haki strength increased by 230%.]

A single Haki clash, and the intensity more than doubled.

What devil's descendant?

Clearly, this was an Overlord Haki experience pack delivered right to his door.

...

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