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Kukuroo Mountain – The Training Grounds Beneath the Manor
The wind howled through the artificial canyon carved into the mountain's underbelly. Fluorescent lights hummed overhead like dying insects, casting long shadows across the blood-stained training ring. Killua Zoldyck stood at the center, silver hair matted with sweat, white tank top clinging to his lean frame. His breathing was steady, but his eyes—those electric blue eyes that could freeze a man's soul—burned with quiet frustration.
"Again."
Silva Zoldyck's voice echoed from the observation platform thirty meters above. The family head didn't raise his tone. He never needed to. The single word carried the weight of a mountain.
Killua didn't reply. He simply dropped into a low stance, knees bent, fingers splayed like claws. Godspeed hummed beneath his skin—electric aura crackling along every nerve. But it wasn't enough. Not anymore.
Not after the reports.
Ronin.
The name had been buzzing through the family's internal channels for weeks. An Enhancer who fought like a demon. Who had crushed Uvogin. Who had stared down Silva and Zeno in Yorknew and lived. Who was currently dismantling Meteor City like it was a playground.
Killua had overheard the butlers whispering. He'd seen the footage Milluki leaked from the Yorknew hotel fight—Susanoo's crimson skeleton shattering buildings, black flames that refused to die. And then the Heaven's Arena posters had gone up. October 1st. Ronin versus Hisoka.
Killua's fists tightened until his knuckles popped.
Why does everyone get to fight the strong ones except me?
He exploded forward.
Godspeed – Full Burst.
Blue lightning wreathed his body. The air screamed. In the span of a heartbeat he crossed the canyon floor, fist coated in Transmutation aura shaped like a razor. The target dummy—a reinforced steel golem enchanted with Zoldyck-grade Nen—barely had time to raise its arms before Killua's strike landed.
CRACK.
The golem's forearm shattered. Shards of metal sprayed like shrapnel. Killua didn't stop. He spun, heel whipping around in a lightning-enhanced roundhouse that caved the golem's chest plate inward. Sparks flew. The construct staggered.
But it wasn't dead.
A hidden emitter node in its torso activated. A pressure cannon fired point-blank.
Killua's eyes narrowed. He twisted mid-air, body folding like origami. The cannon blast grazed his shoulder, burning a shallow line across his skin. Pain was irrelevant. He landed on the golem's shoulder, drove both palms into its neck, and unleashed Whirlwind Palm—a technique he'd stolen from watching Silva's Dragon Head Caricature and refined with pure speed.
The golem's head exploded in a shower of circuitry and steel.
Killua dropped to the ground, aura flickering out. His chest heaved once. Twice. Then he straightened, wiping blood from the corner of his mouth with the back of his hand.
"Progression log," he muttered to the hidden recorder. "Session 47. Godspeed duration: 11 minutes 42 seconds. New technique integration: 68% efficiency. Physical limiters… still holding me back."
Above, Silva watched without expression. But in the shadows behind him, a pair of dead-cat eyes gleamed with something far less professional.
Illumi Zoldyck.
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Illumi's Private Quarters – Two Hours Later
The room was sterile. White walls, no windows, a single hospital-style bed. Illumi sat cross-legged on the floor, silver needles arranged in perfect geometric patterns around him. Each needle carried a microscopic transmitter. Each transmitter fed live footage from the training canyon.
He had watched every second of Killua's session.
A soft, almost loving smile curved his lips—the same smile he wore when Killua was four and had first learned to kill a target without hesitation.
"My little brother is growing so fast," Illumi whispered. His voice was gentle, the way one might speak to a cherished pet. "But that Enhancer… Ronin. He's a threat. He looked at Killua once at the Arena. Just once. And Killua smiled back."
The needles trembled. Aura leaked from Illumi like smoke.
He had already tried to kill Ronin once. Failed. Maha had been forced to step in at Heaven's Arena. Illumi's shoulder still ached where he had torn it free from that frozen space. The memory made his smile widen.
"Big brother will protect you, Kil. Even if I have to become the villain of your story."
He stood, needles vanishing into his sleeves. His phone buzzed—Milluki reporting new intel on Ronin's latest power spike. Illumi read it once, then deleted the message.
No need to worry Killua with details.
---
The Next Morning – Family Breakfast Hall
Killua shoved rice into his mouth mechanically, eyes glued to the tablet Milluki had "accidentally" left on the table. The screen showed leaked Heaven's Arena footage: Ronin's Susanoo ribcage tanking everything Hisoka could throw.
"...that skeletal thing is cheating," Killua muttered. "But the speed… he's faster than me in Godspeed bursts. How?"
A hand landed on his shoulder—light, almost affectionate.
"You're comparing yourself to an outsider again, Kil?" Illumi's voice was honeyed poison. He leaned down, breath brushing Killua's ear. "You don't need to. You're perfect exactly as you are. My perfect little brother."
Killua shrugged the hand off without looking up. "I'm not perfect. I lost to Gon. I froze against the old man's dragon. And now some random Kurta guy is out there fighting Spiders and Hisoka like it's a game."
Illumi's eyes darkened. The temperature in the hall seemed to drop.
"Kurta… Ronin." The name came out like a curse. "He's nothing. A bug who got lucky with some eyes. If he ever looks at you the wrong way again—"
"Big brother." Killua finally turned, voice flat. "You're doing the creepy thing again."
Illumi blinked. Then smiled wider. "Is it creepy to want my little brother to stay safe? To stay mine?"
Killua sighed and went back to the tablet.
Across the table, Silva watched the exchange with hooded eyes. Zeno, seated beside him, chuckled softly. "That boy's bro-con is getting worse. Should we intervene?"
Silva shook his head once. "Let him. Illumi's obsession keeps him sharp. And if Ronin ever becomes a real problem… the family has contingencies."
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Underground Training Vault #7 – Three Days Later
Killua had locked the vault from the inside. No cameras. No recorders. Just him, a mountain of weighted training gear, and the new technique he was trying to birth.
Godspeed – Thunderbolt Step.
He needed something faster than pure linear bursts. Something that let him change direction mid-movement without losing momentum. He'd studied the footage of Ronin's Lightning Style Chakra Mode—how the guy could pivot like lightning itself.
Killua closed his eyes. Aura surged. Electricity danced across his skin.
Step.
He vanished.
Reappeared ten meters left.
Step.
Twenty meters right, mid-air twist.
Step.
The vault wall cracked as he slammed into it shoulder-first. Blood trickled from his nose. He grinned through the pain.
"Better. Still not enough."
Behind the one-way mirror hidden in the ceiling, Illumi watched with unblinking eyes. He had bypassed every security protocol Killua set. Of course he had.
His fingers twitched. A needle appeared between them.
Just one. A tiny suggestion. To make him rest. To make him stay small and safe and—
Killua suddenly looked up. Straight at the mirror.
"I know you're there, big brother."
Illumi froze.
Killua wiped the blood from his nose. "If you're gonna stalk me, at least help me train. Or are you scared I'll get stronger than you?"
The words were a challenge.
Illumi's smile returned—soft, adoring, terrifying.
The vault door unlocked from the outside. Illumi stepped in, needles already spinning between his fingers.
"Very well, Kil. Big brother will play with you today."
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Training Montage – The Following Week
Day 1: Illumi vs Killua – Pure taijutsu. Illumi held back. Killua still ended up pinned to the wall with seven needles in non-vital points. "You're hesitating," Illumi whispered. "Don't hesitate with me. I can take it."
Day 3: Killua unlocked a partial Thunderbolt Step variant—short teleport-like dashes using Godspeed feedback loops. Illumi countered by turning his own body into a living needle trap. Every time Killua dashed close, a new silver spike appeared exactly where his vital points would land. "Predictable," Illumi cooed. "But cute."
Day 5: Killua finally landed a clean hit—Godspeed-enhanced Four-Finger Pierce straight to Illumi's solar plexus. Illumi coughed blood, smiled, and hugged him anyway. "My little brother is so strong now… but please don't leave me behind."
Day 7: Full spar. No holding back on either side.
The vault shook. Lightning clashed against silver needles. Killua's new technique let him feint, dash, and strike from three directions at once. Illumi responded by turning the entire floor into a web of hidden Rhythm Echo afterimages and needle mines.
At the climax, Killua activated Godspeed – Overdrive, aura output spiking beyond anything he'd managed before. He blurred straight through Illumi's defenses and drove a palm strike into his brother's chest.
Illumi flew back, slammed into the wall, and slid down, leaving a red smear.
For a second, silence.
Then Illumi laughed—soft, broken, delighted.
"Kil… you've surpassed my expectations again."
He stood, blood dripping from his mouth, and walked over to ruffle Killua's hair with a trembling hand.
"I'm so proud. But… if you ever use that strength against the family… or against me…"
The needle in Illumi's other hand pressed gently against Killua's throat. Not hard enough to break skin. Just enough to remind.
"I'll have to love you a little harder."
Killua stared into those dead eyes and felt the familiar chill.
He didn't flinch.
"Try it," he said quietly. "I'm not a kid anymore."
Illumi's smile never wavered.
"That's what makes you perfect."
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October 1st – Heaven's Arena Day (Parallel to Main Story Chapter 123)
While Ronin and Hisoka tore the 223rd floor apart, Killua sat on the family viewing balcony, tablet in hand, watching the live feed.
Illumi sat right beside him, shoulder pressed against his little brother's like they were glued.
Every time Ronin used Susanoo, Illumi's grip on Killua's arm tightened.
Every time the crowd roared Ronin's name, Illumi's aura flickered with killing intent.
Killua felt it all.
And for the first time, he didn't pull away.
Instead he muttered, "One day… I'm gonna fight that guy. And I'm gonna win."
Illumi's voice was soft as silk.
"Only if big brother lets you."
Killua smirked.
"We'll see."
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