One piece: Black Cat

The acrid smell of gunpowder hung thick in the salt air as bullets ricocheted off the deck planks with sharp pings and clangs. The merchant vessel rocked gently beneath the chaos, its disguise as an innocent trading ship long since abandoned.

"What the hell is this brat?!" A gruff voice cut through the mayhem, desperation creeping into the gangster's tone.

"The bullets aren't working on him!" another shouted, his rifle trembling in sweaty palms.

Daz Bones moved through the enemy ranks like a living blade, his arms gleaming silver in the afternoon sun. Each swing sent sparks flying as steel met steel, the metallic screech echoing across the deck.

"This is an order from the captain," Daz said, his voice calm despite the violence surrounding him. "I will eliminate you all."

Spark Claw!

His blade-fingers carved through the air with deadly precision. A gangster's scream pierced the battle's din as he crumpled to the deck, clutching his wounded shoulder.

"This guy's a Devil Fruit user?!" someone gasped. "Isn't he just one of those brats playing at being pirates?!"

Above them, translucent and ethereal, Perona's ghost form drifted with an almost playful malice. Her hollow spirits descended upon the remaining attackers like harbingers of despair.

"I'm worthless," one gangster suddenly wailed, dropping his weapon as tears streamed down his face. "A pathetic insect that deserves to be crushed..."

"I'm truly sorry for walking on the same ground as you all," another sobbed, falling to his knees.

"Why was trash like me ever born...?" The despair spread like a plague through their ranks.

"You guys, pull yourselves together!" their leader barked, but his voice cracked with rising panic. "You're just fighting a bunch of kids! If only—"

"I'm so sorry for breathing..." he finished weakly, the ghost's power overwhelming his will.

"Horo horo horo!" Perona's laughter tinkled like broken glass. "The captain warned us about a surprise attack, but they're all small fry!"

Below, Daz paused mid-strike, his blade-arm gleaming in the sunlight. The weight of his own power seemed to settle on his shoulders like a heavy cloak.

"Hey, Daz." Perona's voice carried down from above, curious. "What's with those eyes?"

Daz glanced at the fallen enemies around him, their bodies twisted and broken. "Nothing. I just understand why the Captain told me not to use this ability too much."

Meanwhile, Nico Robin emerged from the ship's hold like a shadow given form. Her dark hair caught the sea breeze as she surveyed the battlefield with calculating eyes.

"There are quite a lot of these intruders," she observed, her voice carrying its usual mysterious undertone. "Where on earth did they come from? How troublesome."

Perona's ghost form flickered closer, leaving a faint chill in the air. "The only thing that bloomed for you was your ears, so I don't know for sure, but it seems like the enemy also has some kind of ability. Soldiers and weapons suddenly appeared from nowhere."

"Robin," Daz called out, wiping blood from his blade-arm, "can't you make your eyes bloom for the Captain?"

Robin shook her head, a strand of hair falling across her face. "I was just about to do that to see what was happening, but I can't get any new limbs to bloom once I'm near the vault."

"I thought the door was the only place that seastone was installed," Daz muttered, his brow furrowing.

Despite the chaos, Robin moved with practiced efficiency. Her sprouted hands appeared and disappeared like flowers blooming in fast-forward, gathering ammunition and valuables from the fallen enemies. Any gangster foolish enough to interfere found themselves either paralyzed by Negative Hollows or blown away by Perona's explosive mini-ghosts.

"Hmm?" Perona tilted her head, studying Robin's unusually bright expression. "What's the matter, Robin? You seem to be in a good mood. Usually you're quite gloomy, which really isn't my preference."

"You're praising and insulting people at the same time," Robin replied with a slight smile. "Very skillful."

The remaining gangsters, who had been keeping their distance and firing from cover, were now scattered across the deck like leaves in a storm—utterly defeated.

"Daz, Perona," Robin said, her voice carrying a warmth that rarely surfaced.

"What is it?" Daz responded.

"Horo?"

"I'm so glad I got to board the Captain's ship."

•~•

Meanwhile, in the Vault...

Castle Tank Charge!

The massive form of Capone Bege thundered forward on mechanical treads, his fortress body gleaming with metallic menace. The confined space amplified every grinding gear and hissing hydraulic.

Slip Kick!

Kuro's leg snapped out in a blur, trying to halt Bege's advance, but the counterforce sent shockwaves up his spine. The impact resonated through the seastone-lined chamber like a thunderclap.

"I knew you'd be tough, but..." Kuro gritted his teeth, feeling the vibration in his bones. "You're incredibly heavy!"

"Of course!" Bege's laughter boomed from his castle-form, the sound echoing off the metal walls. "I'm a castle human who ate the Shiro-Shiro Fruit!"

Around them, the gangsters Kuro had dispatched earlier lay motionless, their unconscious forms testament to his speed. The smart move had been to clear them out first—now he could focus entirely on the real threat.

Bege's agility surprised him. For someone who could transform into a massive fortress, his movements were remarkably fluid and precise.

"A flimsy, lightweight castle isn't really a castle!" Bege declared, his treads churning against the floor.

"That's certainly true," Kuro admitted, adjusting his stance. "By the way, aren't you going to send out any more soldiers?"

"I sent everyone I could to stop your crew," Bege replied, his tone grudgingly respectful. "But it looks like they were completely defeated. You have impressive subordinates, Kuro."

A warm pride swelled in Kuro's chest. "They're friends I'm proud of."

With Daz and Perona up there, subduing ordinary fighters would be child's play. Just knowing they could handle themselves made this entire battle worthwhile. Even in this seastone-lined room that should suppress Devil Fruit powers, they seemed to be fighting with considerable strength. When he'd brought Perona aboard, she'd adapted immediately to their fighting style.

Still, Daz would need to work hard if there were any unexpected attacks from outside. Robin needed protection, and Kuro needed to find more people he could trust completely.

"What's wrong, Kuro?" Bege's eyes gleamed with anticipation. "Lost in thought?!"

"Ah—"

Bege's cannon ports opened, and his remaining interior soldiers fired in unison. The muzzle flashes lit up the confined space like deadly fireworks.

Kuro's legs moved in practiced arcs, each motion honed by his previous battles with marines. Every bullet was either kicked aside or deflected, the metallic pings creating a staccato rhythm against the walls.

"I was thinking about our next voyage," Kuro said casually, not even breathing hard.

"Then don't worry!" Bege's laughter rumbled like distant thunder. "Your next voyage will be with me! I'll prepare the most flashy and exciting adventure possible!"

His treads made that distinctive gyurrarara sound as they spun against the floor.

Why does a castle have tank treads? Kuro wondered absently. There aren't any tanks in medieval castles!

"Even if we sail together, isn't your work mostly on land?" Kuro pointed out. "I prefer the sea!"

Cat Bite Combo.

This was his evolved version of the storm kick technique he'd learned from that naval battle—a two-hit combination where his right foot struck first, followed immediately by his supporting left foot in a devastating follow-up.

If one hit doesn't work, then two hits should do the trick—

"That's lukewarm, Kuro!!"

"Still not enough, huh?"

Bege's tank charge repelled both strikes, sending Kuro skidding backward across the smooth floor.

Damn it! Frustration burned in his chest. My weakness—low attack power—is working against me again!

Just when he'd learned the pseudo-Storm Kick and made real progress, he had to face Capone Bege, user of the Castle-Castle Fruit! In terms of pure defensive capability, Bege was among the toughest opponents in the entire series. He probably hadn't reached his full potential yet, but he was still no ordinary foe for someone at Kuro's level in the West Blue!

The sound of muffled sobs and groans drifted from the chained marines, but they all watched the battle with silent intensity.

If anyone out there still believes in the pirate spirit, Kuro thought, then I have to live up to those expectations. Otherwise, I'll be heading straight for a tragic backstory or the hell route! I have to get through this no matter what!

But in this world, the only ways to increase power were intensive training, using techniques you'd never tried before, or creating entirely new ones. He'd been training constantly, but facing someone of this caliber so soon was unexpected!

He couldn't even get through Daz's defenses in sparring matches! Moreover, his techniques were basically imitations of the "Six Powers," which could only be improved through relentless practice.

A method to immediately increase his power without training, using only the skills he currently possessed... was there really something so convenient?

Help me, someone...

Wait—there was something!

"It's not just talent," Bege said, breathing heavily as his tank treads slowed. "You're genuinely strong. I acknowledge that, Kuro."

The repeated ramming attacks had taken their toll on Kuro's legs, and his movements were gradually becoming more labored. Sweat glistened on his forehead despite the cool air in the vault.

"When you made your subordinates bow down earlier, I thought you were just some cocky brat who figured he could take me one-on-one. But look at this!" Bege's voice carried genuine amazement. "You alone have defeated all of my subordinates! The ones I let out are now your prisoners!"

The remaining gangsters lay scattered around them, groaning and clutching various injuries. Those who had tried to cripple Kuro on their boss's orders had been dispatched in seconds.

"If you had grown just a little more, the power of that kick would have been on a completely different level," Bege continued, respect coloring his tone. "Perhaps it would have even penetrated my castle walls slightly. That's how much potential your technique showed. It was the first time my soldiers inside were actually scared."

Kuro's breathing was indeed ragged. His "Slipping Foot" technique—the source of his nickname—was incredibly stamina-intensive. Using it for transportation was one thing, but employing it frequently in combat was exhausting.

"But unfortunately for you, Kuro!" Bege's eyes blazed with fighting spirit. "You met me at the wrong time!"

"No, that's not right, Bege."

Despite his fatigue, Kuro stood straight and defiant before the chained marines, his presence unwavering.

"I couldn't have been more fortunate to have the opportunity to cross blades with a man like Capone Bege—such a formidable opponent."

He began tapping the floor with his right toe, testing its surface and feeling the vibrations travel up through his leg.

"I've always been confident in my speed. My attacks worked fine against ordinary humans. So I was constantly thinking about what I'd do when facing a tougher enemy—one against whom my speed alone wouldn't be enough."

Instead of his usual stance with his left foot as the pivot, he shifted his weight to his right foot for attacking.

"If my attacks don't reach you, I'll keep trying until they do."

He began to spin in place, slowly at first.

"What is he...?" one of the gangsters muttered, confusion written across his battered face.

Their expressions shifted from skepticism to disbelief as Kuro's rotation accelerated beyond anything they'd seen before.

The spinning became a blur of motion, and the first thing they noticed was his feet beginning to glow red from the friction and heat. As he spun faster, the glow intensified, shifting from red to brilliant blue.

Ji, ji, ji! Ji, ji, ji, ji, ji, ji!!!

The sound was piercing—like the angry chirping of a thousand birds, sharp enough to make everyone in the room wince. The heat radiating from his spinning form made the air shimmer.

When Kuro finally stopped, crackling electricity danced around his right foot like captured lightning.

"So this is what happens when I push my legs to their absolute limit," he said, slightly out of breath but grinning fearlessly.

"Are you using some kind of hidden weapon?!" Bege demanded, his earlier confidence shaken.

"No," Kuro replied, adjusting his glasses with one hand. "It was a gamble."

The electric energy crackled and sparked, casting dancing shadows on the walls.

"Take this, Capone Bege."

"Castle Wall—"

Winter Cat: Lightning Flash Strike!

For the first time, Kuro's kick pierced through Bege's defenses that had previously deflected every attack. The electric-charged strike found its mark, and a cry of genuine pain escaped from Bege's mouth along with a trickle of blood.

"Guh...agh..."

"I told you, Bege," Kuro said, his voice steady despite his exhaustion.

"I'll break through with the pride of a pirate."

"Haha..." Bege's laugh was weak but filled with admiration. "I thought so... you really are..."

"...the real deal."

•~•

The Aftermath

"Boss!" The panicked cry echoed through the chamber.

"You brat! How dare you do that to Bege-san!!"

Just when they thought the battle was over, the gangsters who had been serving as artillery inside Bege's castle form suddenly emerged. Whether his power had deactivated from the damage or they'd simply jumped out didn't matter.

Stop. Don't shoot.

Kuro's shoulders sagged with exhaustion. Kicking bullets aside one by one was tedious work, and he was already spent.

"Stop," he said firmly. "This is settled."

He could have easily knocked them all down in his current state, but the matter had been decided between the leaders. Continuing would be disrespectful to the spirit of their duel.

"Rather than fighting, I want you to focus on rescuing and treating the wounded," Kuro continued. "If you don't hurry, this situation will only get more complicated."

"What?!" several voices chorused in confusion.

"No, seriously—if we don't move quickly, we'll all be in trouble."

The weight of the situation pressed down on them like the humid sea air. Kuro could smell the metallic tang of blood mixing with the salt breeze that somehow found its way into the sealed chamber.

"There's no way the people on this ship alone could have arranged the buying and selling of marine slaves," he explained patiently. "And naturally, they'd be extremely careful about information leaks."

It was obvious that the gangster organization was much larger, and there had to be significant corruption within the Navy itself to make this operation possible.

"I searched the upper levels of the ship before coming to face Capone Bege, but I couldn't find any Den Den Mushi. They were probably afraid of having their location tracked through wiretapping."

Because of that paranoid security, they couldn't even call for backup when things went wrong.

"Even so, they'd have to conduct some kind of status check," Kuro continued, his analytical mind working through the implications. "When the ship that was supposed to return to port after completing the sale runs late... this is a high-risk business, after all. It wouldn't be unusual for them to send detailed verification."

In fact, it would be surprising if another vessel wasn't already en route to investigate the delay.

"We should both clear out of this area as soon as possible."

The gang members exchanged uncertain glances, clearly torn between their loyalty to their fallen boss and the logic of Kuro's words.

Damn, Kuro thought, I'm sure this would be more convincing if I looked a bit older...

"Mr. Bege and I clashed with our respective principles on the line," he said, putting as much authority into his voice as possible. "Even though you were all present, the bosses faced each other and settled things according to the code."

"If we continue fighting after the duel has been decided, this entire encounter will tarnish both my crew's reputation and Mr. Bege's name."

As expected, when the topic turned to reputation—to honor and respect—they seemed to reluctantly begin understanding. The leader clicked his tongue in frustration but muttered, "Hey, let's go," and they rushed off to tend to their fallen comrades, starting with Bege.

Kuro watched them go, then turned toward the chained marines with a weary but genuine smile.

"Sorry for keeping you waiting, friends."

The weight of responsibility settled on his shoulders, but it felt good—like purpose finally finding its place.

---

Author Notes: 

I really didn't think coming up with a name for that technique would be so difficult...