[FATE] OP Demon King Across Multiverse!

The Ryūdōji Temple, beneath Mount Enzō—Fuyuki City's Holy Grail War battleground.

Standing before the gaping cavern, its depths pulsing with arcane energy, the Great Holy Grail lay hidden at the very heart of this underground sanctuary of magic.

Even Mash Kyrielight couldn't suppress a breath of awe.

"This is… incredible. It almost looks like a natural cave… Is this truly where the Greater Grail has always been?"

"This place is both natural and artificial," Olga Marie interjected. "Magus workshops have been built here for generations."

As a scion of the Animusphere family, one of the Twelve Lords of the Clock Tower, Olga was no stranger to magecraft workshops.

After all, her father was the Lord of the Astromancy Department—a legacy she was meant to inherit.

The Fuyuki Holy Grail had long been known to the Mage's Association, so it wasn't surprising that Olga was familiar with its history.

But Ryuu didn't share in their awe.

He remained on guard.

This was enemy territory—there was no way it would be left undefended.

Even if Artoria herself didn't care for traps, EMIYA most certainly would.

And, as if answering his thoughts—

Fou suddenly bristled.

The tiny beast on Mash's shoulder arched its back, fur on end, growling softly.

Danger was near.

Ryuu's eyes narrowed. He turned swiftly—

And there, perched atop a twisted tree, stood EMIYA—clad in red and black, eyes steeled with resolve and regret.

For a moment, hesitation flickered in his gaze.

But then—it was gone.

His resolve hardened.

"This time," EMIYA said, his voice cold, "you're not getting past me."

Ryuu smirked.

"Called it. You really can't let us through, huh?"

Mash tensed beside him. "So as long as we get close to the Grail… he appears."

As expected. EMIYA wasn't here to win the Grail himself—he was here to stop them.

But why? Was this inhibition's will? Or was EMIYA still trying to protect Saber?

"Are you still her loyal watchdog?" Ryuu taunted.

"I have no loyalty to anyone," EMIYA replied, voice steady. "I'm simply here to eliminate intruders. And to kill you."

His gaze locked onto Ryuu—and for the first time, Ryuu saw it.

Pure, unfiltered hatred.

He frowned. "Tch. What the hell did I do to piss you off so much? I mean, sure, I killed Shirou Emiya once, but that was just business."

Cú Chulainn stepped forward, planting his staff into the ground.

"Doesn't matter why," the Lancer-turned-Caster muttered. "If you wanna stop us, Archer, then let's settle this here."

EMIYA pulled Kanshō from thin air, notching it to his longbow.

"I don't have time for pleasantries."

He loosened the shot.

A spiral blade screamed through the air, targeting Ryuu's heart.

But Ryuu didn't move.

Mash stepped forward, raising her shield instinctively—

But before the blade could connect—

FWOOSH!

A fireball from Cú Chulainn detonated the projectile midair.

"Oi, Archer," Cú Chulainn grinned, staff humming with magic.

"You got the wrong guy. Your fight's with me."

EMIYA landed from the trees, projecting another set of blades.

"So you finally decided to fight seriously, huh?"

Cú Chulainn rolled his shoulders, spinning his staff expertly.

"More like I'm just sick of your face."

"Leave this to me. You all go ahead."

Mash's eyes widened. "But—"

"No buts, little missy," Cú Chulainn grinned. "I've got history with this guy. Let me enjoy myself a little."

Ryuu frowned. "Oi, we could finish him faster if—"

Cú Chulainn raised a hand.

"Listen, Master. I've been hiding behind you for too long."

For the first time, his voice was serious.

"A Servant's job is to fight for their Master. You fight your battles. This one's mine."

Ryuu stared at him.

Then—slowly—he nodded.

He raised his Command Seal—and his Geass-marked eye gleamed.

"Then, in the name of the Demon King—Cú Chulainn, bring me victory."

Power surged through Cú Chulainn's veins.

"That's more like it."

Ryuu turned. "Let's go."

"Stay alive, dog," EMIYA muttered.

"Heh. You too, faker."

Cú Chulainn charged forward.

EMIYA responded in kind.

Sparks flew as staff met twin blades—a clash of pure speed and skill.

Both warriors were monsters in agility, their weapons blurring too fast for the human eye.

EMIYA weaved through attacks, striking at Cú Chulainn's vitals—

But the Celtic warrior countered flawlessly, evading each blow.

Then—

A sudden Rune flared—Cú Chulainn had pre-etched a trap into the battlefield.

EMIYA's foot hit a sigil—and a burst of flame erupted beneath him.

"Tch!" He barely managed to leap back in time.

"You thought I'd only fight you in melee?" Cú Chulainn grinned, blue runes glowing on his arms.

"You really must be an idiot."

EMIYA narrowed his eyes. "You're not Lancer anymore."

"Nope. But I'm still me."

Cú Chulainn thrust his staff forward, releasing a wave of arcane fire.

EMIYA dodged, projecting Caladbolg—a spiraled, distorted sword, primed to unleash destruction.

With a single motion, he fired it like an arrow.

BOOOOOOOM!

The blast engulfed the battlefield.

But when the smoke cleared—

Cú Chulainn stood, untouched.

"Didn't you hear me?" he grinned. "I'm Caster now."

A wall of runes shimmered behind him, having absorbed the attack.

EMIYA clicked his tongue.

"This'll take a while."

Cú Chulainn spun his staff, assuming a new stance.

"Then let's enjoy it, shall we?"

---

Meanwhile…

Ryuu and the others disappeared into the depths of the temple.

As EMIYA tried to pursue, Cú Chulainn blocked his path once again.

"If you wanna get past me—"

He grinned, bloodlust in his eyes.

"—you're gonna have to kill me first."

EMIYA exhaled, closing his eyes briefly—then, he raised his blades once more.

The battle between two legends—

A Heroic Spirit turned Caster.

A Counter Guardian turned Servant.

Two warriors who despised each other—

Clashed once again.

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