[FATE] OP Demon King Across Multiverse!

Weeks had passed since the death of Darius III. Ryuu had gradually settled into his current routine—hunting skeletal soldiers daily to rack up Demon King Points, training under Cú Chulainn in Rune Magic, and occasionally clashing with Archer in high-speed duels.

It almost felt like his old days in another world. Before he became a Demon King, he had lived like this alongside Nitta and Sayuri. Those memories were once warm, yet they were tainted by betrayal.

That fateful day… when they forced him into the Sword-Forging Furnace, leaving him no choice but to fall into the abyss.

His hands clenched into fists. A cold, murderous aura surged from within him.

"Oi, Master, what's with the killing intent all of a sudden?" Cú Chulainn asked warily.

Ryuu exhaled, loosening his fists. "Nothing, just… remembering something."

Cú Chulainn didn't pry further. He had learned that Ryuu carried too many secrets.

---

Meanwhile, not far from them…

A young girl with short red hair and golden-orange eyes lay unconscious on the cold pavement of a ruined Fuyuki street.

Beside her stood a knight clad in purple armor, a towering shield resting in her grip. Her vigilant eyes scanned the surroundings while a small, fluffy creature perched on her shoulder.

"Senpai! Senpai, wake up!" the knight, Mash Kyrielight, called out anxiously.

Gu Dazi—Fujimaru Ritsuka, the last Master of Chaldea—groaned as she slowly opened her eyes.

"Ma…sh…? Are we safe? Where are we?"

Mash breathed a sigh of relief. "It seems our Rayshift was successful. According to my analysis, we've arrived in Fuyuki City, 2004."

As she helped Ritsuka up, a blue holographic screen flickered on the girl's Chaldea Combat Uniform.

"Hey, can you hear me?" A slightly frantic yet familiar voice rang through the comms.

"Doctor Roman!" Ritsuka perked up.

"This is Mash Kyrielight, Shielder-class Servant! Reporting from Singularity F! Fujimaru Ritsuka is with me—she's safe!" Mash responded formally.

"Confirmed… but wait, Fujimaru also Rayshifted?! No, no, no, this wasn't in the plan! Without proper combat experience, the stress should've crushed you!" Doctor Romani Archaman ranted.

"I'm fine," Ritsuka assured him, smiling. "Honestly, I don't feel any different."

"...You're built different," Romani muttered.

Suddenly, an ominous clattering echoed from the alleyways.

The skeletal army had noticed them.

"Doctor, we have hostiles incoming!" Mash reported, gripping her shield.

"Ugh, damn it! Ritsuka, Mash, listen carefully! Head toward the nearest spiritual leyline convergence point—the signal here is weak, and we might lose contact any seco—"

Static.

The transmission cut out.

"Mash, what do we do?!" Ritsuka asked, eyes darting nervously between the approaching undead.

Mash tightened her grip on her shield.

"Orders, Senpai?"

Ritsuka swallowed. There was only one choice.

"Defend and counterattack, Mash!"

"Understood!"

With a battle cry, Mash charged forward, her shield blasting skeletal soldiers into dust with each impact.

But the city's undead swarm was endless.

Their fight had just begun.

---

Not far from them…

Ryuu and Cú Chulainn sensed an intense magical disturbance.

"Yo, Master… something's happening over there," Cú Chulainn noted.

Ryuu's eyes gleamed. "Chaldea… you're finally here."

"Hah? Chaldea? What the hell are you on about?"

Before Ryuu could answer, the night sky ignited.

A barrage of red mana arrows rained down on Mash and Ritsuka's position, forcing Mash to hunker behind her shield.

"Archer again," Ryuu muttered. "This time, he's not aiming at us."

Cú Chulainn frowned. "Wait—there's someone else alive?"

"Yeah," Ryuu smirked. "The last Master of humanity."

Cú Chulainn blinked. "...The hell does that mean?"

Ryuu didn't explain. Instead, he sprinted toward the battlefield.

"Come on, Caster, time to play hero."

---

At the battlefield…

Mash was struggling.

Her new powers as a Demi-Servant were still unstable, and Archer's projectiles showed no mercy.

Another volley of arrows rained down.

Damn… I can't keep up!

Just as she braced for impact—

A black inferno erupted.

The oncoming mana arrows were incinerated mid-air, dispersing into embers.

Ritsuka and Mash turned, eyes widening.

A young man with jet-black scales creeping along his arms and golden, dragon-like pupils emerged from the smoke.

Beside him, a blue-robed figure grinned wildly, spinning a mage's staff like a spear.

"Hey, Archer!" Ryuu called out. "Picking on rookies now? That's low, even for you."

From the rooftops, Red Archer—Emiya—lowered his bow, his red cloak billowing behind him.

"Annoying as always, huh, Demon King?"

---

Cú Chulainn leaped forward, runes glowing at his fingertips. "Come down here and fight, you red bastard!"

Archer scoffed, dodging a barrage of fireballs before summoning his twin blades.

Cú Chulainn lunged, his staff clashing against Kanshou and Bakuya. Sparks flew as their weapons met in rapid succession.

Ryuu turned toward the stunned girls. "Oi, Chaldeans, you good?"

Mash blinked in confusion. "Chaldeans…? How do you—?"

"Explanations later." Ryuu smirked. "For now, stay put and watch."

---

The battle between Archer and Cú Chulainn intensified.

Though the latter was technically a Caster, he fought like a Lancer, skillfully wielding his staff like a spear.

"You're so bad at being a mage, it's almost impressive," Archer taunted.

Cú Chulainn scoffed. "Like you're any better at archery!"

Meanwhile, Ryuu crossed his arms, watching closely. He wasn't in a rush.

This wasn't his fight.

His eyes shifted to Ritsuka Fujimaru.

The last Master of humanity. A "hero" destined to save the world.

The moment he saw her, something inside him twisted—disgust, fear, and something else.

He clenched his fist.

Demons and heroes were born as natural enemies.

Even if she was just an ordinary human now… Ryuu could feel the potential burning inside her.

A potential that would one day grow powerful enough to erase him from existence.

He turned away.

---

Archer suddenly leapt back, disengaging.

"The message is delivered. I have no reason to stay."

Ryuu's eyes narrowed. Message?

Archer's gaze met his. "Saber wants you at the Great Grail beneath Mount Enzō."

"...Us?" Ryuu asked.

"You'll find out when you get there," Archer replied, vanishing into the shadows.

Cú Chulainn spat. "Bastard just ran again!"

But Ryuu wasn't listening.

His golden pupils reflected the burning city.

Saber had made her move.

The gears of fate had begun to turn.

And humanity's final battle was about to begin.

=======

Support and read advance chapters on Patreon.com/Zexxxxy