[FATE] OP Demon King Across Multiverse!

For the past month, Ryuu and Cú Chulainn had been constantly on the move.

They had fought countless battles—clashing with Archer time and time again.

Yet each time, Emiya managed to escape.

Cú Chulainn was furious.

Ryuu, on the other hand—had other concerns.

---

During their downtime, Ryuu trained under Cú Chulainn, learning the fundamentals of rune magic.

And as Cú Chulainn had warned—

"It's not that easy, brat."

Even after weeks of practice, Ryuu could barely summon a fireball.

Still—battle after battle, the two developed a deadly synergy in combat.

But one thing still infuriated Cú Chulainn.

Every single time they fought an enemy, Ryuu always landed the finishing blow.

Cú Chulainn's patience had worn thin.

"Oi, Master. We agreed I'd get the next kill."

Ryuu shrugged. "Oh? My body just moved on its own."

Cú Chulainn's eye twitched.

"Bastard. You've been saying that for a MONTH!"

Ryuu snickered.

Not my fault you're too slow, Caster.

---

After a brief rest, the two relocated again.

They knew Archer was lurking somewhere nearby.

That bastard had Clairvoyance, always appearing at the worst possible moment—

Always attacking after they finished a battle.

This time—Ryuu and Cú Chulainn were prepared.

But then—Ryuu noticed something odd.

He paused.

"…Wait. Something's off."

Cú Chulainn glanced around. "Hm? What is it?"

Ryuu frowned.

"No skeleton soldiers. Not a single one."

Before Cú Chulainn could respond—

A piercing scream echoed in the distance.

"Aaaaaaaahhhhhh!!"

A human scream.

Followed by—

"CLANK! CLANK!"

The sound of metal armor rattling.

---

From the shadows, skeletal warriors marched forward.

Unlike the mindless undead from before—

These skeletons wore armor. Held weapons. Moved in perfect formation.

Shields in the front.

Spears in the middle.

Greatswords in the back.

They were an army.

And then—

A thunderous roar erupted from deep within the city.

Ryuu's expression darkened.

"I know who's behind this."

Cú Chulainn's grip tightened around his staff. "Who?"

Ryuu's eyes gleamed.

"Rider. Darius III—the Last King of Persia."

Cú Chulainn gritted his teeth.

"Tch. This guy's bad news."

The skeleton warriors charged.

Cú Chulainn reacted instantly, summoning flaming runes and launching fireballs into the horde.

"BOOM!"

Flames erupted—shattering the undead.

But—

The skeletons didn't die.

Even when their bones shattered, they reassembled.

And kept coming.

---

"They're regenerating?!"

Cú Chulainn cursed.

Ryuu's eyes narrowed.

"Geass won't work either. They have no minds to control."

"What now, Master? We can't win like this!"

Ryuu smirked.

"We burn them to ASH."

---

Ryuu activated his second Blood Awakening.

His golden pupils flared.

Cú Chulainn felt the temperature rise.

"Here we go..."

Ryuu took a deep breath.

"Flame Spirit Scorching Blaze!"

A massive black flame explosion engulfed the battlefield.

Every skeleton in its path was incinerated.

Only ash remained.

"Hah… That worked."

Cú Chulainn nodded.

Taking Ryuu's lead, he adjusted his rune magic—

Summoning flames instead of wind.

Together, they torched their way through the horde.

Then—

A second, deeper roar shook the ground.

THOOM.

A towering figure emerged.

His skin dark as night, covered in golden tribal markings.

A golden battle-axe gleamed in his hand.

His burning eyes locked onto Ryuu and Cú Chulainn.

"That must be Rider," Cú Chulainn muttered.

Ryuu exhaled sharply.

"Yeah. And he's got a Noble Phantasm."

---

A horn blast echoed through the battlefield.

A massive war elephant materialized beneath Darius III.

Its body pulsed with skeletal energy.

Its ivory tusks gleamed with pure destruction.

Hundreds of soulless eyes blinked from its monstrous frame.

It was—

A living siege engine.

Cú Chulainn braced himself.

"We need a plan, Master!"

Ryuu's expression hardened.

"There's only one option."

"We fight."

Ryuu ignited his flames, clearing a path.

"Caster, focus on Rider! I'll handle the skeletons!"

Cú Chulainn nodded.

The war elephant roared.

Darius charged forward.

Cú Chulainn fired a wind blade at Darius' chest.

But—

"CLANG!"

The blade barely scratched him.

"This guy… is a monster."

Ryuu grinned.

"Good. So am I."

His golden pupils burned.

The final battle against Rider had begun.

=======

Support and read advance chapters on Patreon.com/Zexxxxy