One Piece: Start with Zanpakutō

"Me?"

"Teacher Zephyr, please forgive me for being blunt."

"I really can't find any shortcomings… I just feel super strong."

Rosen thought it over seriously first, then said this with a slightly embarrassed expression.

He had already mastered all Three Forms of Haki and their techniques.

For boosting Haki strength, he had the Haki Core.

All that was left was to keep following the routine, train daily, eat well, and let the Haki Seeds Practice and mature. 

Not long after, he will have Armament Haki as strong as Garp's, Observation Haki like Katakuri's, and Conqueror's Haki on par with Shanks or Roger.

When it came to Haki… he really had no flaws.

Especially compared to other students in Zephyr's class, he was basically unstoppable.

Gion: "…"

Tokikake: "…"

The two wanted to object… but in the end, they had nothing to say.

After fighting Rosen, they realized he really had no weaknesses — at least not when it came to Haki.

"You're using 'that master' Tokikake as your measuring stick, so of course you think you have no weaknesses."

"Don't compare with him. Use me as your benchmark."

"Do you still feel super strong now?"

Zephyr wasn't surprised at all by Rosen's answer.

Indeed, within the Naval Academy, Rosen was far, far ahead.

Even among the Marine Headquarters' elites, he could already secure a place.

And once his Haki strength caught up with his skills, it wouldn't just be a "place to stand" — he'd be standing right at the top, able to trade blows with Admirals.

That's not even considering his Arms-Arms Fruit.

"What if the person you fought today wasn't Gion or Tokikake, but me?"

"Would your Armament Haki-coated punch work?"

"Could you severely injure me with a single hit?"

To drive the point home, Zephyr flexed his pitch-black, hardened arm and clenched his fist. A chilling metallic scraping sound rang out.

"..."

Gion silently opened her mouth.

She felt a little insulted, but seeing Zephyr show off his blackened wrist, she wisely chose to stay quiet.

"Facing Teacher Zephyr?"

"That… wouldn't work."

Rosen's expression turned serious immediately.

"Then what would you do?"

"Even if I don't use my full strength, if I only use Armament Haki equal to yours for defense, how will you break through it?"

Zephyr stared at him, his voice slow and deliberate.

"Increasing attack power…"

Rosen's eyes lit up slightly.

"Then let me ask you again."

"Before your Haki strength has improved dramatically, how can you increase your attack power?"

"Let alone if I use full force… even if I defend with an Armament Haki of the same strength as yours, how are you going to break it?"

Zephyr's eyes sparkled with satisfaction.

"How to increase attack power…"

Rosen fell into deep thought, and his consciousness naturally poured into his Armament Haki.

While pondering how to increase his attack power, he carefully observed the flow of Haki.

Gradually, he became completely immersed in the world of Haki, completely ignoring the outside world.

"You…"

Zephyr was stunned.

He originally just wanted Rosen to temporarily set aside Haki and start practicing physical combat skills.

After all, to fully unleash the ultimate power of Haki in real battle, you needed not just Haki techniques, but also strong physical skills, swordsmanship, or devil fruit mastery.

As someone who had dominated the top ranks with just Haki and physical power, Zephyr naturally hoped Rosen would follow that path rather than rely too heavily on his fruit, like Borsalino.

But what happened instead?

A single disagreement — and this monster decided to comprehend a new technique on the spot.

[Your comprehension is extraordinary. By combining the four Armament Haki techniques with Ultra Instinct, you have pioneered a unique Armament Haki technique: Blut Arterie (Active Blood Dress).]

[Blut Arterie (Active Blood Dress): By using the Ultra Instinct control over Armament Haki, inject Haki into your blood vessels, evolving it into actual offensive power, greatly amplifying destructive force.]

(Requires ultimate-level Haki control. If others practice it, they will suffer permanent damage to all blood vessels.)

Rosen read the information that appeared in his mind, and his eyes lit up.

Blut Arterie (Active Blood Dress)?

Wasn't this exactly what he needed to increase attack power?

For offense, use the Blut Arterie (Active Blood Dress) combined with Hardening, Emission, and Internal Destruction to evolve into ultimate attack power.

For defense, use the Blut Vene (Calm Blood Dress) combined with Hardening, Emission, and Internal Destruction to evolve into ultimate defense.

His fists and kicks would become his strongest attacks.

Wherever he stood would become his strongest fortress.

After all, both Blut Vene and Blut Arterie (Active Blood Dress) were Armament Haki techniques — not only could they be layered with other Armament techniques, but also used together with Conqueror's Haki Infusion.

Even facing Teacher Zephyr himself, no problem.

Even if Zephyr had Armament Haki twice as strong as Rosen's, he could still break through with one punch.

"Teacher Zephyr, I've figured it out."

"Whether it's about boosting attack power or breaking defense, I can do it now."

Rosen raised his head, meeting Zephyr's gaze, and spoke slowly and clearly.

"What did you figure out?"

Zephyr had already guessed it, but still asked.

"The sixth Armament Haki technique I just comprehended."

"Blut Arterie (Active Blood Dress)."

"By evolving ultimate attack power, I can break through any defense with one punch."

Rosen's eyes blazed with an unstoppable light.

"The sixth… Armament Haki technique…?"

Gion and Tokikake were both completely dumbfounded.

Was this gap even humanly possible?

Teacher Zephyr had asked them to summarize and reflect — result? They were told to go practice Observation Haki for the afternoon.

But what about Rosen?

At first, he declared he had no flaws.

In the end, Zephyr could only be used as a hypothetical opponent for him to imagine.

And the result?

Rosen didn't go off for any "special training" — he literally created the sixth Armament Haki technique on the spot after a simple disagreement.

Meanwhile, the two of them hadn't even finished learning the basic four techniques yet!

"Is it the same as the Blut Vene (Calm Blood Dress)?"

Zephyr understood instantly.

Even without Rosen explaining further, he knew —

The Blut Arterie (Active Blood Dress) and Blut Vene (Calm Blood Dress) were two sides of the same coin. Both involved injecting Haki into blood vessels. The difference?

Blut Vene (Calm Blood Dress) evolved ultimate defense inside the blood vessels.

Blut Arterie (Active Blood Dress) evolved the ultimate offense.

Even monsters like Kaido and Big Mom would never dare touch this technique.

Injecting Haki directly into blood vessels was equivalent to a self-destructive attack on one's own body.

No matter how tough your body was — diamond, iron balloon, or natural element — you'd basically be digging your own grave.

Only Rosen could do this.

If anyone else tried — whether Four Emperors or Admirals — they'd instantly explode from the inside.

"Exactly."

"The difference is only one thing — offense versus defense."

"Even if your Haki is three times stronger than mine, Teacher Zephyr, I can still break your defense with one punch."

Rosen's voice was calm but carried absolute confidence.

After hearing this, Zephyr's expression grew complicated.

He didn't doubt Rosen's words at all — he just didn't know whether to laugh or cry.

Originally, he had only meant for Rosen to focus more on basic combat skills.

But instead, this monster disciple had ended up creating the sixth Armament Haki technique to evolve ultimate offense — just because of a single disagreement.

This was like asking a student to study math… and they went and discovered a new law of physics instead.

Even Zephyr, who considered himself a monster and had seen countless geniuses, couldn't help but curse inwardly at this moment.

This kid's comprehension really is like a damn monster!

...

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