Grand Zi-O and Neo Decade Complete Form 21 ignited simultaneously, converting their golden and silver-magenta weight into raw, kinetic fury. They charged, two streaks of rivaling brilliance tearing through the wasteland. As they ran, both braced their right fists against their belts, channeling the vast, cascading energies of the Heisei era into a single, concentrated point.
In less than the blink of an eye, the several hundred meters of scorched earth between them simply vanished.
They met at the center of the crater. Two fists, heavy with the weight of twenty years of history, collided with a sickening, metallic crack.
BOOM!
A titanic shockwave erupted from the point of impact, a physical wall of pressure that shrieked across the landscape. The very mountain beneath their boots groaned and shuddered, tectonic plates weeping under the spiritual strain of two Sovereigns at war.
In the heart of the city—a sprawling labyrinth of neon lights and bustling crowds—the residents paused. A dull, rhythmic thud echoed in the distance, vibrating through the soles of their shoes and rattling the glass of high-rise windows.
To the mundane masses, it was merely an anomaly. Perhaps a distant demolition or a localized gas explosion. Most shrugged it off, assuming some festive celebration was underway in a neighboring ward.
"Was that a firework? It sounded huge," someone muttered, squinting toward the darkened silhouette of the distant mountains.
"Funny," another replied, checking their phone. "I hear the boom, but I don't see any light in the sky."
Back in the desolate wild, the struggle remained a stalemate. Decade's fist was locked against Rin's, the air between them ionizing into a haze of white-hot sparks. Neither gave an inch.
Then, the dance shifted.
Rin reached out with his left hand, his fingers brushing the golden relief of Kamen Rider Kuuga etched into his thigh. Simultaneously, Decade's hand blurred, sliding a card of Kuuga on his Neo DecaDriver
They broke the lock, leaping backward to reset the field. As they landed, the air beside Decade distorted into a pool of shifting shadows. From the darkness stepped a black-clad warrior with golden horns and eyes like dying embers—Kamen Rider Kuuga, Ultimate Form.
Opposite him, Rin Kuga didn't just summon a shadow; he opened the vaults of heaven. A dozen golden circular portals, shimmering with the geometry of a clock face, manifested behind him.
The gates slid open with a synchronized mechanical hiss. From the golden void, a barrage of Rising Titan Swords screamed forth, propelled by the King's will. They lanced through the air like a localized meteor shower, targeting both Decade and his Ultimate puppet.
Rin wasn't just a user of this power; he was an architect of it. Drawing upon his deep knowledge of the Rider chronicles, he treated the Grand Zi-O form not as a mere suit of armor, but as a command center. He didn't just fight; he orchestrated.
"You've got to be kidding me..." Tsukasa's voice crackled through his helmet, flavored with a rare note of genuine disbelief. "You can use the gates like that?"
There was no time for shock. The Rising Titan Swords descended like divine judgment. Decade and the Ultimate Kuuga were forced into a frantic defensive rhythm, parrying and shattering the golden blades as they rained down in a relentless, overwhelming swarm. The sheer volume of the assault was suffocating.
Sensing the opening, Rin didn't wait. He plunged his hand into the shimmering air and drew the Saikyo Zikan Girade.
He crossed the distance in a heartbeat. Caught in the midst of parrying a golden sword, Decade's guard faltered for a fraction of a second. It was all Rin needed. He gripped the hilt with both hands, his boots bracing against the cracked earth, and delivered a savage, horizontal cleave.
CRACK!
The impact sent Decade skidding backward through the dirt, his armor groaning under the force. The summoned Ultimate Kuuga, having served no purpose other than to be a distraction, dissolved into golden particles and vanished.
Tsukasa performed a series of rapid backflips in mid-air, landing in a crouch and digging his fingers into the soil to arrest his slide. He stood slowly, the silver portraits on his chest reflecting the dim light. This was not the green youth he had encountered in other timelines. This Zi-O was a monster of combat efficiency—a man who played with the Grand form's capabilities like a virtuoso on a piano.
Rin didn't press the advantage. Instead, he casually tossed the Saikyo Zikan Girade aside, the heavy blade vanishing back into the temporal void before it even hit the ground. He stood tall, the golden reliefs on his armor gleaming with a cold, tectonic light.
"Trading blows like this is a waste of both our time," Rin said, his voice echoing with the finality of a decree. "Let's settle this with a single strike. One deciding moment to see whose causality holds more weight."
Beneath the magenta-and-silver helmet, Tsukasa Kadoya let out a sharp, jagged laugh.
"Heh. You took the words right out of my mouth, kid. Let's see what you've got!"