Kai soared through the open sky, golden wings slicing through the wind as the vast ocean stretched endlessly beneath him. The New World churned with restless waves, violent and unpredictable, as if testing every soul daring enough to cross it. High above, he adjusted the Oni Mask, feeling its power surge through him as his body expanded into his adult form.
From this day forward, the Oni Samurai would walk the seas.
Below him, a pirate ship cut through the waters, its black sails fluttering against the harsh sea breeze. Kai's crimson eyes gleamed behind the mask as he descended like a falling star. He gripped Akatsuki and landed heavily on the deck, the wood cracking slightly beneath his boots.
"Yooo," he called casually, resting the blade on his shoulder. "I need a ship. Would you be kind enough to let me borrow it?"
The pirates froze, staring at the towering masked warrior who had appeared out of nowhere. The captain, a broad-shouldered man with a jagged scar across his face, stepped forward and spat on the deck.
"Who the fuck are you?"
Kai tilted his head slightly, as though mildly offended. "Well, people in Wano used to call me Oni Samurai. You can also call me that."
"Oni Samurai my foot!" the captain roared and lunged forward with a heavy axe raised high. "Kill him!"
Steel flashed in the sunlight.
Kai moved once.
Akatsuki sang through the air in a single clean arc. The captain's body split apart before he even realized the strike had landed. Silence followed—brief, suffocating silence—before screams erupted across the deck.
"Monster!" one pirate shouted.
Kai exhaled slowly. "You attacked first."
He dashed forward, kicking one pirate straight into the sea before sidestepping a spear thrust. He grabbed another by the collar and hurled him overboard as well. The sea swallowed them greedily.
A burly swordsman charged from the side. "You think you can just walk onto our ship?!"
Kai blocked the strike effortlessly. "You sail the New World and ask that question?"
Their blades clashed repeatedly, sparks scattering like fireworks. The swordsman gritted his teeth. "You're no samurai… you're a demon!"
"Close enough."
Kai twisted his blade and disarmed him, then delivered a powerful kick that sent him flying into the mast. The mast cracked, and the man slumped unconscious.
He deliberately spared a handful of stronger fighters, testing his reflexes and sharpening his instincts. Combat was no longer survival—it was refinement.
Within minutes, the deck was silent except for the crashing waves. Kai dragged the surviving captain—barely breathing—and tossed him overboard.
"Swim," Kai said calmly. "If you live, tell them who did this."
The pirate coughed seawater and stared upward in terror. "Y-You… what are you trying to do?"
Kai's voice turned cold. "Spread my name."
He adjusted the sails and steered the captured ship toward the Grand Line's deeper waters.
---
The New World did not welcome him kindly.
Violent currents smashed against the hull, forcing Kai to abandon one ship after another as monstrous waves tore them apart. Lightning split the sky without warning, and sea kings surfaced like ancient guardians testing his resolve.
"Energetic today, aren't you?" Kai muttered while gripping the wheel during a storm. "Fine. Let's dance."
He leapt across collapsing decks, commandeering fresh pirate vessels whenever one sank beneath him. Each encounter ended the same way—defeat, humiliation, and a captain left alive to carry his legend.
Some drowned.
Some survived.
But every single one spoke the same name.
Oni Samurai.
---
Weeks later, Kai encountered a fleet unlike the rest. Their ships were older, weathered by decades of battle, their flags faded but proud. The pirates aboard them carried scars that told stories of an older era.
"Oi! Identify yourself!" shouted a white-bearded lookout from the crow's nest.
Kai stepped forward, mask gleaming. "Just passing through. Leave your ship, and I'll leave you breathing."
The fleet erupted into laughter.
"Brat," their captain growled, stepping onto the deck with a massive saber resting on his shoulder. "Do you know who we are?"
"No," Kai replied calmly. "But you're about to know who I am."
The captain roared and charged.
Their clash shook the deck violently, wood splintering beneath their feet. The captain was strong—far stronger than the average pirate Kai had faced. Their blades moved at blinding speeds, exchanging dozens of strikes in seconds.
"You've got skill!" the captain barked. "Who taught you?"
Kai smirked. "A ghost."
The captain's eyes narrowed. "That stance… that grip…"
Kai's blade crackled with black lightning as he infused it with Conqueror's Haki. The air trembled.
"Kamushari."
The slash tore through the battlefield like divine judgment.
The captain barely managed to raise his saber before being sent flying across the sea, crashing through two ships before disappearing into the horizon.
The vice-captain staggered backward, eyes wide with horror. "That move… I've seen that before…"
A chill ran down his spine.
"That's the Pirate King's—"
Before he could finish, he dove into the ocean and swam away in terror.
Kai stood silently as the remaining crew stared in shock.
"Finally," Kai muttered. "Someone old enough to remember."
He sheathed Akatsuki slowly, satisfaction flickering beneath his mask. This was the reaction he had been waiting for.
---
The rumors spread like wildfire.
Old pirates whispered in taverns. Survivors of a bygone era trembled at the mention of Kamushari being used again. The name Oni Samurai became synonymous with a haunting memory long buried beneath time.
Kai continued hunting, seeking veterans who had once crossed paths with legends. Each battle sharpened his technique, his haki control, his endurance.
And somewhere in the shadows of the New World, a certain name stirred.
Golden Lion Shiki.
"If he hears this," Kai said softly to himself while standing on a conquered deck, "he'll come."
---
Aboard the Moby Dick
On the deck of the Moby Dick, the sea breeze carried news like an ill omen.
Marco landed lightly beside the massive figure of Whitebeard, who sat drinking from a barrel-sized sake cup.
"Pops, there's a guy in the New World calling himself 'Oni Samurai.' Many old-time pirates have been defeated by him."
Whitebeard chuckled deeply. "Gurararara! The sea always has some strong people, Marco. And if it's someone from Wano, it's natural they're strong. No need to cause so much ruckus."
Marco inhaled slowly. "Pops… he is using Kamushari everywhere. Many old-time survivors have confirmed it. It's the same as Roger's—just weaker."
Whitebeard's laughter stopped.
His eyes sharpened. "Are you sure?"
"Yes, Pops."
"Gurarararara… the sea never stops showing something unexpected. Who would have thought someone would still be using his swordsmanship?"
Marco folded his arms. "Do we investigate?"
Whitebeard took another deep drink. "No. Let the sea test him first."
But his gaze turned distant.
"Roger… what kind of brat did you leave behind?"
---
Marineford – Sengoku's Office
"What do you mean someone is using Roger's swordsmanship?!" Sengoku roared, slamming his desk so hard papers scattered everywhere.
The marine soldier trembled. "Sir… many old-time pirates have confirmed it."
"Damn Roger! Even after dying, he isn't letting the Marines live peacefully!" Sengoku growled.
Suddenly, the door slammed open as Garp burst through it.
"Where is Roger?!" he shouted.
Sengoku's mouth twitched violently. "You bastard! Stop breaking my damn door!"
"Shut up and tell me where that Roger is!"
"It's not Roger, you idiot! It's someone using his swordsmanship!"
"Then tell me where he is!"
"In the New World!" Sengoku roared.
Before he could finish another sentence, Garp had already sprinted toward the port.
"Roger! I'm coming, you bastard!"
"Stop, Garp! Don't you dare run off to the New World!" Sengoku yelled.
But Garp was gone.
Sengoku collapsed into his chair, clutching his forehead. "This sea… it's cursed."
---
Back in the New World, Kai stood atop yet another conquered vessel as the sunset painted the horizon red. The wind carried whispers of his name farther than he could see.
He rested Akatsuki on his shoulder and smiled faintly beneath the mask.
"Come," he murmured to the vast ocean. "Old legends, fallen kings… come test me."
The sea answered with thunder.
And the name Oni Samurai echoed across the New World like a challenge to the era itself.