Cycle Zero : reincarnated as the Demon King, Now What?

The New Dungeon

“Let’s see what today’s quest will be,” Diablo said to himself as he headed to the guild.

When he got there, he saw nobody inside. The hall that was usually filled with adventurers swapping stories and haggling over quest boards stood almost empty. He went to find Isyrae. She told him that every available adventurer had been sent to explore a newly discovered dungeon.

“Please come with me to the guild master’s office,” she said. “He’ll tell you the details himself.”

The two of them walked together through the quiet halls and into the guild master’s office. Vasryn Kael’dathor sat behind his desk, a map spread out in front of him.

“A new dungeon was discovered yesterday by a group of adventurers,” the guild master said. “It’s been classified as a B rank dungeon, so we’ve sent everyone to deal with it. What that means for you is simple. You need to be there too. The soldiers of Velmoor won’t be assisting us this time, so we need every capable adventurer we can get.”

“Where is this dungeon located?” Diablo asked.

The guild master pointed to a location within the borders of Velmoor. “That’s where it is. Now get going.”

Diablo left the office and made his way there as quickly as he could. When he arrived, he found dozens of adventurers already locked in battle, cutting down waves of goblins and ogres that spilled out from the dungeon’s mouth. He joined the fight without hesitation.

The goblins came in packs, snarling and swinging crude blades, easy to cut down but relentless in number. The ogres were slower but far more dangerous, each swing of their clubs enough to crush a careless adventurer. Diablo moved through them with practiced restraint, cutting down a goblin here, parrying an ogre’s club there, always careful to fight like a skilled but ordinary adventurer rather than the demon lord he truly was.

“It’s the new guy! The one who saved Natsu’s guild!” someone shouted from the crowd of adventurers still fighting.

Diablo kept fighting. He could have ended the entire battle in a matter of seconds if he wanted to, but he needed to keep up the act. He couldn’t afford to let anyone see how strong he truly was.

Bit by bit, he pushed forward, cutting a path through the horde until he found himself moving deeper into the dungeon, leaving the rest of the adventurers behind him.

Once inside, he continued fighting for roughly fifteen minutes, cutting through goblins, ogres, and the occasional stray beast that had made its home in the dungeon’s winding corridors. Eventually, the passage opened into a wide chamber, and at its far end stood a massive gate, the boss gate of the dungeon.

The moment he stepped through it, the gate slammed shut behind him with a deafening groan of stone against stone. There was no way out, and no way for anyone else to come in.

From the shadows, a voice emerged.

“Well, well. Who is my lucky prey? I hope you came prepared to die.”

A surge of energy rippled through the chamber as the voice spoke again. “What is your name?”

“My name is Diablo, the demon lord,” he answered evenly. “And I’ve come here to kill you.”

“Diablo? What a joke. Demon lord? That’s hilarious.” A low laugh echoed off the stone walls.

“What is your name?” Diablo asked.

“I am the greater vampire, Kronos. Many have heard my name, and none have lived to tell the tale.” He gestured toward a pile of bleached bones piled in the corner of the room, remnants of those who had come before. With a flick of his wrist, he summoned five hundred goblins to deal with Diablo.

Within a single second, every last one of them lay dead.

“You’re going to need more than just goblins to stop me,” Diablo said, a wide smile spreading across his face.

Kronos’s expression darkened, and he began summoning wave after wave of goblins, each one falling just as quickly as the last. No matter how many he conjured, Diablo cut them down without slowing his pace, without so much as breaking a sweat.

“Sword art,” Kronos finally intoned, raising both arms. “Sword of a Thousand Warriors.”

A thousand blades materialized in the air above him, each one glinting with malevolent light, all of them turning to point directly at Diablo.

“Let’s see you handle this,” Kronos said with a sneer.

The swords flew toward him in a storm of steel. Diablo simply snapped his fingers, and every single blade crumbled into dust before it could reach him.

From within that settling cloud of dust, two red eyes began to glow, and laughter rolled out of the haze. “Is that all you’ve got? I expected more.” The dust swirled and reformed, taking shape once more into the figure of Kronos. “You’ve entertained me enough. It’s about time you die.”

In an instant, Kronos dropped dead, collapsing to the floor as though something had reached out and snuffed out his life in a single stroke.

A moment later, he stood back up, laughing. “Hahaha, you don’t know who you’re messing with. I am the greater vampire, Kronos. I’m immortal, you idiot. What makes you think you can kill me?”

Diablo let out a short laugh of his own. “Well, it seems you’re not entirely useless after all.”

He blitzed forward, closing the distance in a heartbeat, sword already drawn. Kronos met him blade to blade, and the two exchanged a flurry of strikes, steel ringing against steel with every clash. Kronos fought with the desperation of a predator who had never once faced a true equal, his movements wild and unpredictable, each strike aimed to maim rather than simply wound. Diablo answered every blow with calm precision, deflecting strikes that would have torn lesser fighters apart, countering with strikes of his own that Kronos barely managed to avoid. Sparks flew where their blades met, and the chamber shook with the force of their exchange.

Kronos lunged low, aiming to gut him, but Diablo sidestepped and brought the flat of his blade down against Kronos’s shoulder hard enough to send him stumbling. The vampire recovered quickly, snarling, and lashed out with a clawed hand that Diablo caught by the wrist, twisting it aside before driving a knee into his ribs. Kronos staggered back, coughing, disbelief written across his face. He had not been struck like that in centuries, if ever.

“I’m getting bored of this,” Diablo finally said, lowering his blade. “You really did interest me for a moment, which is why I wasn’t planning on killing you so soon. But now, die.”

“Unique skill, Instant Death, has been used.”

Kronos’s heart stopped beating mid breath. He crumpled to the ground, and this time, he did not rise again.

A voice echoed inside Diablo’s head. “You’ve gained ten thousand experience points from defeating the greater vampire Kronos. You’ve also gained all of his abilities.”

With the boss dealt with, Diablo left the dungeon.

When he emerged, everyone was waiting outside. The moment they saw him, a wave of questions broke out.

“I’ve already defeated the dungeon boss,” he told them simply. “We’re done here.”

The crowd erupted into cheers, though a few faces in the back scowled with poorly hidden jealousy.

He reported back to the guild master, who paid him for the job and, on the spot, promoted him to D rank.

To celebrate, the guild master decided to treat everyone.

“Today’s drinks are on me,” he announced. “So everybody, take as much as you want.”

“That’s our guild master for you!” the crowd shouted, raising their mugs.

After several minutes of drinking and swapping stories about the fight, Diablo excused himself and left the guild, intending to head back to the tavern to rest. On his way, he felt the presence of a group of people trailing him at a distance.

Why are they stalking me? he thought to himself, deliberately leading them away from the guild and into a quieter part of the city. Even after several turns down empty streets, he could still feel them following.

“I know you’re out there,” he said aloud. “Show yourselves.”

A man stepped out from the shadows.

“Why are you following me?” Diablo asked. “And I know I’m being followed by more than just you.”

“I’m impressed you noticed.” The man gave a slow, mocking bow. “My name is Ashwood, leader of the Roaring Lions guild. We’re an A rank party. That dungeon you conquered was supposed to be ours. Have you come here just to steal our popularity? I want you to leave this guild now, or you’re going to wish you hadn’t crossed us.”

“I don’t think you’re in any position to tell me what to do,” Diablo said, unmoved.

“I’ll ask you one time. Stop following our jobs, and I’ll overlook what happened today.”

From the shadows behind him, someone lunged, attempting to strike Diablo from behind. He sidestepped easily, dodging the blow without even turning to look. The rest of the Roaring Lions party emerged from hiding, spreading out to surround him.

“You would have been wise to stay away from this guild,” Ashwood said, drawing his sword. “Now you’re going to pay for it with your life.”

He came in first with a jumping attack, swinging his blade down in a wide arc. At the same time, the two mages behind him raised their hands, fireballs already forming in their palms, while the alchemist hung back near the rear, vials of restorative tonics ready in case anyone needed healing mid fight.

“Then I shall fight all of you,” Diablo said, drawing his sword from his pocket dimension with a flick of his wrist.

He met Ashwood’s downward swing with his own blade, the impact sending a shockwave rippling outward that cracked the cobblestones beneath their feet. Before Ashwood could recover, the first fireball streaked toward Diablo’s back. He twisted aside without breaking his stance against Ashwood, letting the fireball scorch harmlessly past him and into a nearby wall.

The second mage tried a different approach, weaving a spell that sent three smaller fireballs arcing toward him from different angles. Diablo spun once, his blade cutting through the air in a wide circle, and every fireball dissolved into smoke and sparks the instant his sword passed through them.

Ashwood pressed forward again, faster this time, raining down a series of quick strikes aimed at Diablo’s shoulders and ribs. Diablo parried each one in turn, his movements unhurried, almost lazy by comparison, though every block landed with enough force to make Ashwood’s arm shudder. He could have ended the fight in a single strike, but he held back deliberately, careful not to kill or maim any of them. He wanted to teach them a lesson, not bury them.

One of the mages, growing desperate, abandoned fire in favor of a spell that conjured a barrage of hardened wind blades, sending them slicing through the air toward Diablo from multiple directions at once. He weaved between them with barely a change in his footing, letting most pass harmlessly by while deflecting the rest with the flat of his blade.

The alchemist finally moved, hurling a vial that shattered at Diablo’s feet, releasing a cloud of numbing gas meant to slow his reflexes. Diablo simply exhaled, and the gas dispersed around him as though blown away by a wind only he could summon.

Ashwood, seeing his party’s efforts failing one after another, let out a frustrated shout and charged in recklessly, abandoning technique for raw aggression. Diablo caught his blade on his own, held it there for a heartbeat, then twisted his wrist sharply enough to send Ashwood’s sword flying from his grip and clattering across the cobblestones.

Before Ashwood could react, Diablo swept his legs out from under him, sending him crashing to the ground. The two mages, seeing their leader fall, tried one final combined spell, weaving their magic together into a single, larger blast of fire. Diablo stepped forward calmly, raised his hand, and caught the blast in his open palm, letting the flames wash harmlessly over his skin before snuffing them out entirely with a simple close of his fist.

The mages stumbled back in shock, and the alchemist, realizing there was nothing left to be done, dropped his remaining vials and raised his hands in surrender.

One by one, the members of the Roaring Lions guild fell, exhausted and thoroughly beaten, until only Ashwood remained standing, swaying on his feet, refusing to admit defeat even as blood trickled from a cut above his brow. Diablo closed the distance one final time and struck him with the flat of his blade across the chest, sending him to the ground alongside the rest of his party.

Silence settled over the street. The entire party of the Roaring Lions guild lay scattered across the cobblestones, defeated.

“I won’t kill you,” Diablo said quietly, looking down at Ashwood.

A moment later, he vanished, teleporting away from the scene and reappearing back at the tavern, leaving the beaten party to pick themselves up in the empty street behind him.