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

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

Systemlast updateLast Updated : 2026-09-28

By:  Donney Updated just now

Language: English
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Ren Kazama died the way most people do in this kind of story, badly and without warning. Twenty-six years old, three energy drinks deep into an all-nighter, he was crossing the street outside his office at 2 AM when a delivery truck ran the red light. He didn’t even feel it. One second he was checking his phone for a client email, the next he was staring at his own crushed umbrella from somewhere above his body. No tunnel of light. No smiling goddess offering him a wish. Just darkness, then cold, then the sensation of something ancient and starving wrapping itself around whatever was left of his soul. When Ren opened his eyes again, he wasn’t looking at a hospital ceiling. He was looking at a throne room built from black stone and bone, lit by torches that burned violet instead of orange. A mirror stood in front of him, and the thing staring back wasn’t human. Red eyes. Skin like ash over embers. A voice, older than the walls around him, echoed in his skull: “The seal has broken. The throne is empty. You will do.” That was it. No explanation, no tutorial, no system window blinking helpfully into existence. Just a title dropped onto him like a curse. Demon King. Ren stared at the throne room full of demons who were already kneeling to him out of terror rather than loyalty, and had exactly one thought. Now what?

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Chapter 1

The Demon Lord Awakens

All the demons were saying, “Our lord has arrived. Our demon lord Diablo has been resurrected.”

Ren sat on the throne, trying to understand what was going on and what he was doing here. “Who the hell is Diablo?” he said to himself. Then, from the crowd of demons, Rias walked toward him and said, “Welcome, my king. We are here to do your bidding.” Ren was quiet for a few minutes. When Rias looked at him, she saw that Ren had already turned red, staring at her chest. Rias said, “Is that what you want? I am here to do your bidding.” Ren snapped back to reality and said, “Yes. I have been reborn, and I have come back to rule this realm.” The whole crowd of demons shouted in response. After the meeting, he told everyone to leave except Rias and said to her, “It’s been so long, I can’t remember much of what happened.” He lied to her.

Rias said, “My lord, you can just use your power to take all the information you want from me.” She said this genuinely. “Really, I can?” he screamed, then calmed himself immediately. “Oh yeah, that ability.”

Then a voice echoed in his head: “Do you want to use the unique skill Telepathy?” He said yes, then touched Rias on her head. Immediately, he saw everything that had happened. After a few seconds, he had everything he needed and told Rias to leave him alone, which she did.

So somehow I’ve been reborn into this so-called Diablo’s body. Well, for now, I guess I know what I’m dealing with and how to act.

That same day, while sitting on his throne, Rias came to him and said, “My lord, we’ve been attacked by the humans again, and they have killed some of our kind.” Ren, who now answered to Diablo, said, “I told you all not to engage at all costs before I died. Now I’m starting to regret saying that. I will handle it myself. I’ll show the world that I have awakened.” He left the chamber in rage. As he was leaving, Rias said, “No need to involve yourself with these humans. I alone can defeat them.”

They quickly got to where the attackers were. When he arrived, he saw about a thousand soldiers, including five hundred holy mages, five hundred enslaved dark elves, and three hundred summoned beasts. He laughed to himself, then flew up into the sky dramatically and said, “I am back, humans. This massacre of my kind shall end today.”

“Who is that? Who is that?” the humans asked among themselves. Then the oldest among them said, “This is Demon Lord Diablo. He was said to have been dead for decades. How is he here?” The leader who had led the armies into the demon realm said, “Attack!”

Just as they were about to attack, Diablo snapped his fingers and said, “Die.” A black aura of force surged toward the soldiers, and in an instant, all one thousand soldiers and five hundred mages were killed.

Then the voice in his head said, “Unique skill Instant Death has been used. You have successfully gained 5000 exp points from killing the humans.” He flew toward the dark elves and summoned beasts and said, “You are free.” He told Rias to take them to Malgorath, also known as the demon realm. Then he dissolved the alliance between the summoned beasts and the humans who had summoned them. “You are also my kind. You shall come with us to Malgorath.”

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TABLE OF CONTENTS
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    95 chapters
    The Demon Lord Awakens
    All the demons were saying, “Our lord has arrived. Our demon lord Diablo has been resurrected.” Ren sat on the throne, trying to understand what was going on and what he was doing here. “Who the hell is Diablo?” he said to himself. Then, from the crowd of demons, Rias walked toward him and said, “Welcome, my king. We are here to do your bidding.” Ren was quiet for a few minutes. When Rias looked at him, she saw that Ren had already turned red, staring at her chest. Rias said, “Is that what you want? I am here to do your bidding.” Ren snapped back to reality and said, “Yes. I have been reborn, and I have come back to rule this realm.” The whole crowd of demons shouted in response. After the meeting, he told everyone to leave except Rias and said to her, “It’s been so long, I can’t remember much of what happened.” He lied to her. Rias said, “My lord, you can just use your power to take all the information you want from me.” She said this genuinely. “Really, I can?” he screamed, then
    last updateLast Updated : 2026-08-02
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    The Bruised Sky
    Before the war, Malgorath was not a wound in the world. It was a realm like any other, its sky the color of a fading bruise, its ground paved in black glass that rang like struck bells under the footsteps of demons who called it home. At its heart stood the Cinder Throne, carved from a single fallen star, and upon it sat King Diablo, the last of the old blood, ruler of a people who had never once crossed into the human lands with intent to conquer. That is the part the histories forget. Or perhaps the part they buried on purpose. The war did not begin with an army. It began with a man named Corvain Ashworth, a human royal advisor whose ambitions outgrew his station. Corvain had discovered a pact scrawled in the founding scrolls of the human kingdom of Velmoor, a pact signed centuries earlier promising Malgorath safe passage through the Veil of Ash in exchange for peace. Corvain saw not a treaty but a weakness. He forged a new scroll, one claiming the demons intended betrayal, and pl
    last updateLast Updated : 2026-08-02
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    What the Throne Was Hiding
    Elenya did not run from the cracking glass. She had spent ninety three years learning that fear made scholars sloppy, and sloppiness got people killed faster than any demon blade. So she knelt very still, pressed her palm flat against the fractured ground, and listened.Beneath the sound of splitting stone, something breathed.It was not a sound she recognized from any bestiary in Malgorath’s archive, and she had read every one of them twice. It was slow, wet, patient, the breathing of something that had been waiting so long it no longer measured time the way living things did. She rose, snatched up the lantern Yoichi had carried across the Veil, and followed the widening crack toward the base of the Cinder Throne.She was not alone for long.“You should not be down here,” said a voice behind her, and Elenya spun with her knife already drawn.The speaker was a demon boy, perhaps sixteen by human reckoning, with ash grey skin and eyes the pale gold of Diablo’s own bloodline. He wore th
    last updateLast Updated : 2026-08-02
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    The Face of a Dead Hero
    The bells of Velmoor were still ringing when the thing wearing Yoichi’s face walked through the eastern gate.No one questioned it. Why would they. The guards on duty, boys barely old enough to shave, had grown up on stories of the man who ended the war, and here he was, alive, walking through the gate at dusk with the last light behind him like something out of a painting. One of them wept openly. Another ran ahead to spread the word before the creature had even reached the market square.Word travels faster than truth. That has always been its cruelest advantage.By the time Reiko, Yoichi’s mother, heard the shouting outside her cottage and stepped into the street, half the eastern quarter had already gathered, and the thing wearing her son’s face was already smiling at her with her son’s own smile, worn thin and wrong in ways only a mother’s eye could have caught.“Mama,” it said, and Reiko’s knees very nearly gave out beneath her.She had spent twelve years bracing for the knock t
    last updateLast Updated : 2026-08-02
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    What the Ash Remembers
    Tamsin Vale did not lower her blade, even as the creature wearing Yoichi’s face began to laugh.“A hunter,” it said, tilting its borrowed head. “How quaint. Do you know how many hunters have come for me over the years, little huntress. Wearing scholar’s charms and grandmother’s warnings and a whole lot of misplaced confidence.”“None of them were me,” Tamsin said.She was younger than her armor suggested, no older than Yoichi had been, with dark hair braided tight against her skull and a scar along her jaw that looked recent, weeks old rather than years. The silver symbols etched into her armor pulsed faintly with each word she spoke, as though the metal itself were listening.Elenya seized the moment of the creature’s distraction to pull Reiko and the still shaking crowd back from the square’s center. Kesh stayed pressed to her side, eyes fixed on Tamsin with the particular hunger of someone who had spent his whole short life surrounded by secrets and had just found one bigger than a
    last updateLast Updated : 2026-08-02
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    The End and the Beginning
    Ren Tanaka was twenty six years old, and for the past three years he had poured every ounce of his energy into his job at a mid sized game production company in Tokyo. He was not the flashiest employee, but he was reliable. The kind of person who stayed late without complaint, who double checked every line of code before submitting it, who believed that hard work would eventually pay off. That morning started like any other. He left his apartment, coffee in hand, and made his way toward the train station. His phone rang halfway there. He glanced at the screen and saw her name. “Hello, Vanessa,” he said, a small smile forming out of habit. She didn’t return the greeting. “It’s over between us,” she said, her voice flat and final. “I don’t want anything to do with a broke man like you.” The line went dead before he could respond. Ren stood frozen on the sidewalk, the phone still pressed to his ear even though there was nothing left to hear. People moved around him like water around
    last updateLast Updated : 2026-08-02
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    Arrival in velmoor
    Diablo called Rias and said to her, “I will be leaving Malgorath for Velmoor. I want you to oversee everything that happens here.” Then he left.He got there using instant teleportation. He entered, and the sky looked clear. He walked for a moment, then saw a little girl being bullied by a blacksmith.“You should do what you’re told, you piece of shit,” he said, whipping her with a whip.Diablo held his hand and said, “Don’t you dare hit her. What has she done?”The blacksmith said, “How is that any of your concern?”Diablo thought for a while, then left. “Oh well, this is not the reason why I am here,” he said to himself.He went to an adventurer’s guild and said he would like to register. He was taken to a special room to test his abilities.“Sir, please touch the orb,” the receptionist said. “We would like to check how much MP you possess.”When he touched it, the orb broke, and she said, “Something like this has never happened before.” She went to call the guild master, and he rus
    last updateLast Updated : 2026-08-02
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    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 dungeo
    last updateLast Updated : 2026-08-02
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    Unwanted (1)
    Diablo walked into the guild, and every eye in the room turned toward him. Whispers spread through the hall faster than he could cross it. Wasn't this the man the Roaring Lions guild claimed had assaulted them the day before?Isyrae approached him before he had taken more than a few steps inside."The guild master would like to see you," she said.He followed her to the office. Once inside, Vasryn Kael'dathor looked up from his desk."Do you know why I called you here?" he asked."I don't know," Diablo said."It's about what you did to the Roaring Lions guild yesterday. Their party leader came to report you. He claims you tailed them and assaulted them. That's why you're here today.""I did no such thing," Diablo said. "I was on my way to the tavern when I noticed them following me. I had to defend myself. They were greedy. They wanted to force me out of the guild, claiming I took their spot, even though I only joined a few days ago."Vasryn studied him for a moment, then nodded slowl
    last updateLast Updated : 2026-08-13
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    Unwanted (2)
    Diablo stood in front of the barrier, shielding the injured party member behind its glow. The fire-breathing snake reared back, coiling its massive body as embers dripped from its jaws like molten rain.He stretched out both hands. A magic circle bloomed in the air before him, its runes spinning faster and faster until light poured out from its center. From within, three beasts emerged, creatures he had freed back in Malgorath, answering his call without hesitation. They landed around him with a heavy thud that cracked the stone floor."Protect the rest of the adventurers," Diablo commanded. "I will handle the snake myself."The beasts obeyed at once, fanning out to form a wall between the wounded party and the rest of the chamber. Diablo turned his attention back to the snake, his expression calm, almost bored.The snake lunged first, jaw wide, fire building in its throat. Diablo sidestepped without effort, the flame scorching the stone where he had stood a moment before. He answered
    last updateLast Updated : 2026-08-15
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