[FATE] OP Demon King Across Multiverse!

As Ryuu sprinted through the ruined streets of Fuyuki City, dark clouds choked the sky, blotting out the sun.

A deep sense of unease settled in his chest.

"This isn't just the Holy Grail War anymore… It's a Singularity."

His Observation Haki flared, instinctively warning him of incoming danger.

The people on the streets had already noticed something was wrong, gazing up at the blackened sky.

Then—

Fire rained from above.

---

Screams erupted from every direction.

"Help! Somebody, please help—!"

"The fire—it's burning everything! AHHHHH!"

"Mom! Mom, where are you?!"

The entire city was in chaos.

Glowing embers descended like falling stars, igniting flesh upon contact.

People burned alive, screaming as their bodies turned to ash.

It was purgatory on Earth.

---

Ryuu wasn't spared from the flames.

But—

His Demon King's power prevented him from burning.

The fire licked at his skin, but his dragon blood refused to succumb.

Snuffing out the embers on his body, he gritted his teeth and took in the hellish scene before him.

"Even as a Demon King, I've never seen devastation on this scale."

It was too late.

He should have realized sooner.

The fifth Holy Grail War was a lie.

This was Singularity F—the prologue to humanity's incineration.

---

Ryuu's mind raced.

"If Leif has already begun the incineration, then Artoria… she's already Blackened."

His hand tightened into a fist, glancing at the Command Seals on the back of his hand.

Could they still work?

Would they still reach her?

His golden eyes narrowed.

"Tch. The irony—asking a Demon King to save the world? I just wanted to summon some followers."

With no more hesitation, he charged toward home.

---

"Tch. Of course, there had to be minions."

A horde of skeleton soldiers materialized at the end of the street, blocking his path.

But these weren't like the undead he fought in his old world.

They were weaker.

Their magic output was low, and their bodies were brittle.

A single swing of Wrath shattered dozens of them into bone dust.

Then—

A familiar chime echoed in his head.

---

[Ding!]

[Congratulations, Host! You have killed 10 skeleton soldiers. You have obtained 50 Demon King Points.]

---

Ryuu blinked.

"Wait. I can farm Demon King Points by killing these things?"

[Affirmative. The Demon King's power thrives on destruction. Any action taken as a Demon King will generate Demon King Points.]

A slow grin spread across his lips.

His golden eyes glowed in the darkness.

"Then let's start the trial of the Demon King."

---

Berserk Blood – Second Activation.

His speed doubled, his strength tripled.

With one massive sweep, he erased another wave of skeletons, their remains scattering like dust in the wind.

More undead began flooding toward him, sensing his overwhelming presence.

But that only made Ryuu laugh harder.

"Come on, you walking point dispensers! Let me farm you properly!"

As the system notifications continued piling up, his Demon King Points skyrocketed.

---

He lost track of time, his blade dancing through waves of enemies.

By the time he finally stopped to catch his breath, the ground was littered with broken skeletons.

Hundreds of them had fallen.

His Demon King Points had surged to 800.

---

"Not bad. I can already afford some abilities."

His system shop now offered various low-tier eye abilities—

X-Ray Vision, Lightning Vision, Clairvoyance.

But none of them were useful in combat.

If he saved up to 1000 points, he could unlock Sharingan (Single Tomoe) or Mystic Eyes of Perception.

Ryuu exhaled sharply.

"No point wasting them on weak skills. I'll save up."

His next move was clear.

Find Cu Chulainn.

If his warning got through, then Cu would be waiting at Fuyuki Bridge.

---

But just as Ryuu turned to leave—

His Observation Haki flared with a warning.

Something was coming.

Fast.

His instincts screamed at him to move.

Ryuu jumped back just in time—

BOOOOOOOM!

A massive explosion erased the spot where he had just been standing.

---

A figure emerged from the flames.

Her presence alone suffocated the air.

Her light blue armor was now black as the void.

Her golden hair had darkened, and her emerald eyes were cold and soulless.

In her hand—

A jet-black holy sword pulsed with malevolent energy.

"I felt it in our last battle, Master. You have the ability to predict the future, don't you?"

Ryuu's heart sank.

"Saber…"

The woman before him—was no longer Artoria Pendragon.

She was Artoria Alter.

---

Ryuu's mind raced.

"How did she find me?"

"Have you forgotten, Master?"

Artoria raised her left hand, revealing her own Command Seals.

"The bond between us remains. It was easy to find you."

Ryuu's expression hardened.

"Then let's test something."

He raised his right hand, the Command Seal glowing red.

"By the power of my Command Seal—Saber, hand over the Holy Grail!"

The red light surged—

But nothing happened.

Artoria smiled.

"That won't work anymore, Master."

Ryuu clicked his tongue.

"Of course not. The Holy Grail made you immune."

Her blackened eyes bore into his soul.

"Now, Master… please die for me."

---

Artoria charged.

The corrupted Excalibur struck faster than lightning.

Ryuu barely had time to block—

And was sent flying into a building.

---

"Shit. She's stronger."

Even with his Berserk Blood, her power was on a different level.

He needed more.

More speed.

More power.

More rage.

His golden eyes burned.

"Fourth Berserk Blood—Activate."

---

Draconic scales surged across his entire body.

His flesh twisted, his bones strengthened.

A pair of blood-red wings tore through his back, spreading wide.

His fingernails sharpened into claws.

His horns extended, curving like a true demon.

The transformation was complete.

This was no longer human Ryuu.

This was—

The Demon King.

Even Artoria hesitated for a split second.

A mistake.

Ryuu's lips curled into a feral grin.

"Now, Saber… let's see if you can withstand this."

---

He raised his clawed hand—

And unleashed everything.

"Word Spirit – Hellflame!"

A massive inferno erupted from his palm, engulfing the battlefield.

The flames roared toward Artoria, the heat warping reality itself.

This was it.

The true battle had begun.

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