Chapter 1: System Error in the Body of the Trash Demon King.
Pain.
That was the first thing that greeted Kenji Tanaka's consciousness.
It wasn't the aching pain of sitting too long in front of a monitor, or the headache of lack of sleep.
This was a fundamental pain, as if every cell in his body was screaming in agony.
It felt like thousands of hot needles were stabbing him from within, and there was a cold, gnawing emptiness in the center of his chest.
"Ugh..."
Kenji tried to open his eyes. The sight that greeted him wasn't the ceiling of his dull Tokyo apartment, but a high, cracked stone ceiling, adorned with cobwebs the size of a fist.
The air smelled musty, like centuries of dust and despair.
He tried to get up, but his body felt incredibly weak.
He looked down and saw his hands—the skin was ashen gray, with sharpened, blackened nails. These weren't his hands.
"S-Sir... Sir Xylos! You... You're finally awake!"
A hoarse, trembling voice called out to him.
Kenji turned his head with difficulty. Beside the stone throne he sat on, a small creature prostrated itself.
The creature looked like a goblin from a fantasy story, with wrinkled green skin, pointed ears, and large, tear-filled eyes.
"Lord Xylos?" Kenji murmured. The voice that came from his own lips sounded foreign—hoarse, weak, but with a deep baritone.
At that moment, a wave of memories that weren't his own crashed into his brain like a tsunami.
Name: Xylos a/l Nocturne.
Position: Seventh Demon King of the Shadowfang Domain.
Status: Loser. Trash. A disgrace to the demon race.
The memory showed Xylos, a genius who became Demon King at the youngest age in history, but arrogant and naive.
He was betrayed by his own fiancée, Lilith, who conspired with his rival Demon General, Lord Malakor. They didn't kill him outright.
They poisoned him with the 'Soul-Rotting Venom,' a vile poison that destroyed his Demon Core, crippled his cultivation, and left him weaker than a lowly imp soldier.
They seized his territory, his army, and his wealth, then banished him back to this ruined Shadowfang Castle to die slowly in disgrace. The pain Kenji felt was the effect of the poison steadily eating away at the last vestiges of Xylos's life force.
The real Xylos had died of despair and pain moments ago.
And somehow, the soul of Kenji Tanaka—an ordinary programmer who died of extreme exhaustion after working 72 hours straight on a game project—was summoned into this empty body.
"This is... Isekai?" Kenji, or now Xylos, laughed bitterly. "From corporate hell to literal hell. At least the scenery is better."
The small goblin, whose name his memory told him was Krix, stared at him in confusion. "Master? What is... Is-se-kai?"
Xylos ignored him. He tried to sense the power within himself. Xylos's memories told him about the cultivation system in this world. Demons cultivate Demonic Qi to strengthen themselves through several levels:
- Imp Refinement Realm
- Fiend Soul Formation Realm
- Mara Core Manifestation Realm
- Asura King Transformation Realm
- And so on, all the way to the legendary Demon Emperor level.
Xylos, who had once been at the peak of the Mara Core Realm, was one step away from becoming an Asura King.
Now...
He could feel the Demon Core within his chest. It should have been a dense, pulsating ball of energy, but now it felt like cracked glass, on the verge of shattering. The remaining Demonic Energy in his body was only a thin thread, placing him at the lowest level of the Imp Refinement Realm. He was truly trash.
" CRASH!!! "
The rickety main door of the throne hall was kicked to pieces. The dim light from outside streamed in, highlighting the silhouettes of several figures striding proudly.
In front of him walked a young demon with long silver hair and luxurious silk clothes. His face was handsome, but his expression was filled with scorn and arrogance. Behind him, two fully armored guards with oppressive auras stood tall.
"Well, well, look who's still breathing," the young demon said mockingly. "I thought trash like you would have long since become the ghouls' meal."
Xylos's memory immediately recognized this person. Valerius, the Young Master of the Crimson Scythe Clan, a lowly noble family that had often curried favor with Xylos during his time in power.
Krix, the goblin, trembled in fear and hid behind the throne. "Y-Young Master Valerius..."
Valerius stepped closer, his powerful aura oppressing the air around them. Xylos could feel it. Valerius was at the mid-stage of the Fiend Soul Formation Realm, several levels above Xylos' current level.
This. The pressure of his energy alone was enough to make it difficult for Xylos to breathe.
"I hear you keep one last precious thing in this ruined castle, Xylos," Valerius said, his eyes glancing at a stone coffin in the corner of the room. "The Shadowfang Heart. Give it to me, and perhaps I will grant you a quick and painless death."
The Shadowfang Heart was the last source of energy for this domain. Without it, the castle would collapse completely, and any remaining magical life within it would cease to exist. It was Xylos's only hope of perhaps recovering some semblance of power.
The old Xylos might have trembled in fear. But Kenji was different. He had spent ten years dealing with arrogant project managers, unreasonable clients, and annoying program bugs. He was fed up with being bullied.
"Leave," Xylos said, his voice weak but cold.
Valerius burst out laughing. "What did you say? Did I hear you right? Trash like you dare order me to leave?"
He gestured to one of his guards. The guard stepped forward and slapped Xylos across the face with the back of his armored hand.
SLAP!
Xylos' head flew to the side. A sharp pain exploded in his cheek, and the taste of blood filled his mouth.
"You should know your place, scum!" Valerius growled. "You're no longer the Demon King. You're nothing but a disgrace waiting to die."
As the pain and humiliation reached their peak, something in Kenji's mind—a programmer's instinct honed over tens of thousands of hours—rebelled. His logical mind instinctively tried to analyze, decipher, and find a solution to this broken 'system.'
And suddenly, the world before his eyes changed.
A transparent turquoise panel, like a computer program's debug console, appeared before him.
[Anomaly Detected: Soul from Another World.]
[Programming Logic Compatible with the World's Arcane Laws.]
[Initializing System Authority: God's Debugger.]
[Activation Successful. Welcome, Administrator.]
Xylos's eyes widened. Before his eyes, Valerius and his guards no longer looked like ordinary demons. They were now covered in lines of code and flowing data.
[Target: Valerius (Crimson Scythe Clan)]
[Cultivation Level: Fiend Soul Formation - Tier 4]
[Main Cultivation Technique: Crimson Scythe Art - Earth Rank]
[Technique Analysis...]
[17 logic vulnerabilities (bugs) and 1 fatal flaw discovered.]
[Fatal Flaw: Reverse circulation in the 31st secondary meridian when executing the 'Crimson Moon Slash' technique. Backlash probability: 87.4%. Backlash Effect: Internal damage, temporary freezing of Demonic Energy.]
Xylos couldn't help the sinister smile that appeared on his bleeding lips. This was his world. This was his game. As long as there were systems and rules, there were bugs to exploit.
"What are you laughing at, worm?" Valerius snapped, his anger fueled by Xylos's smile.
"I'm laughing at your stupidity," Xylos replied calmly. He wiped the blood from his lips with the back of his hand. "Your family's Scarlet Crescent Art... what a flawed technique. I wonder how your clan has survived so long with such a shaky foundation."
Valerius's face paled, then flushed with anger. "Insolent! How dare you insult my family's technique! How did trash like you know about it?!"
"I know more than you imagine," Xylos said, his previously dull eyes now shining with a sharp, cold intelligence. "For example, every time you use your ultimate move, you must feel a stabbing pain in your left shoulder, right? That's not a side effect. It's a bug—a fundamental design flaw that will destroy you one day."
Valerius staggered back as if struck. How could Xylos know such a secret? It was something only the elders of his clan knew!
"You... YOU'RE COURTING DEATH!" Valerius roared, his rage and fear exploding. He didn't care anymore. He had to silence Xylos now. Blood-red demonic energy exploded from his body, forming a giant energy scythe in his hand.
"Die! RED MOON SLASH!"
Valerius swung his scythe. The room shook. This was an attack that could easily cleave Xylos and his throne in two.
Krix screamed in terror. But Xylos remained calm. The panel before his eyes worked rapidly.
[Fatal Threat Detected.]
[Finding a Solution...]
[Option 1: Evade (Probability of Success: 0.1%)]
[Option 2: Defend (Probability of Success: 0%)]
[Option 3: Initiate 'Force Reboot' on the Demon Core. Rewrite the damaged energy circulation pathways. Risk: Permanent system failure (Death). Probability of Success: 12.7%]
Only 12.7%? In his old life, Kenji would never have released code with such a high failure rate.
But now, this was the only option.
"System, execute Option 3!" he thought.
[Command Accepted. Initiating 'Force Reboot'...]
[Warning: Extreme pain will occur.]
It was as if an inferno had erupted within his chest. His fractured Demon Core was forced to rotate. His meridian pathways, clogged with poison, were being forcibly torn apart and reattached. The pain was a thousand times worse than before. Xylos roared, not out of fear, but out of pure agony.
In Valerius's eyes, Xylos looked like nothing more than a dying worm. He smiled with satisfaction.
But then, something extraordinary happened. A pitch-black, pure aura exploded from Xylos's body. The 'Soul-Rotting Venom' poison that had accumulated in his body seemed to be 'cleansed' by this reboot, transformed into pure fuel for his Demon Core. The cracks in his core hadn't healed, but its surface now glowed with a steady black light.
[Reboot Successful.] Demon Core System stabilized.]
[Cultivation Enhanced: Imp Refinement Realm - Level 1 -> Level 5]
[New Technique Generated from Poison Data Analysis: 'Touch of Corruption'.]
All this happened in an instant. Valerius's Scarlet Moon Slash was mere inches from Xylos's neck.
With his newfound strength, Xylos didn't dodge. He raised a finger. His fingertip was enveloped in a small, swirling wisp of black energy. It was 'Touch of Corruption', a technique born from his understanding of the poison that nearly killed him.
He wasn't targeting the energy scythe. The system had revealed its weak point. He was targeting Valerius's wrist, precisely where his energy circulation bug was located.
TING!
Xylos's fingertip, enveloped in black energy, met Valerius's wrist.
For Valerius, it felt like a dam had burst. The Demonic Energy he had been mobilizing for his ultimate move suddenly reversed, flowing wildly through his meridians. The giant energy scythe in his hand flickered and then vanished.
"ARGGGHHH!"
Valerius spat out a mouthful of black blood and was thrown backward, crashing hard into the wall. His right arm was completely paralyzed, enveloped in a thin, black aura that continued to erode his energy.
The throne hall fell silent. Valerius's two guards froze in place, their mouths agape in disbelief. Krix peered out from behind the throne, his large eyes wide with astonishment.
Xylos slowly rose from his throne. His body still ached, but strength now flowed within him. He walked casually past the collapsed Valerius and stared coldly at his two guards.
"Take your worthless master away," Xylos said, his voice now strong and authoritative. "And deliver a message to the Crimson Scythe Clan. Today's debt will be repaid a thousandfold in the future."
The two guards trembled, then hurriedly carried the semi-conscious Valerius and fled the castle.
After they left, Xylos finally let himself gasp for breath. The gamble had drained all his energy. But he had succeeded. He had survived.
Krix ran to him, prostrate himself and sobbing with emotion. "Lord Xylos! Your power... you..."
"This is just the beginning, Krix," Xylos interrupted, his eyes staring off into the distance, toward the domain that had been taken from him.
His face may have been that of Demon King Xylos, but his soul was that of Kenji, the programmer. And he had just discovered the greatest flaw in this world: everyone underestimated him.
Before his eyes, a new notification from his system appeared, glowing with golden light.
[Main Quest Published: Debugging the World]
[First Mission: Reclaim the Demon Throne.]
[Description: This world's system is riddled with corrupt 'code' and arrogant 'users' who exploit it. As an Administrator, your task is to rewrite your destiny. Repair your foundation, gather your strength, and reclaim what's yours.]
[Initial Reward: Administrator Starter Pack.]
Xylos smiled. Not the weak smile of Xylos before, but the confident smile of a programmer who had just discovered the most challenging and exciting project of his life.
"Alright, System," he whispered. "Let's begin the debugging process."
Chapter 1:End