The rain fell hard on the city streets. Riku Tanaka stood at the edge of the sidewalk, soaked from head to toe. His cheap office suit clung to his skin, heavy and cold. In one hand, he held a broken umbrella. In the other, he cradled a tiny kitten.
He smiled.
"At least you're safe now," he whispered.
The kitten meowed weakly, its body trembling. It had almost been hit by a speeding truck. Riku had jumped without thinking. His body hurt all over from the fall, but he didn't care.
Then, he heard a sound—screeching tires.
Riku looked up.
Another truck was coming, too fast. The driver didn't see him in time. Everything happened in a blur. Light. Noise. Pain.
And then… silence.
---
Darkness.
Empty and endless.
Riku floated in nothing. He couldn't feel his body. He couldn't move or speak.
Is this death?
He had no regrets. He hated his job, his life, his loneliness. If he could choose, he'd rather be a rock than go back to that office again.
Suddenly, something answered him.
> [Rebirth confirmed. Unique soul detected.] [You have been chosen as a Dungeon Core.] [Initializing system...]
Dungeon Core? Riku thought. Like in those games...?
A bright light filled the void. Riku felt himself pulled downward—faster and faster—like falling through a tunnel of stars.
When the light faded, he found himself somewhere else.
---
A dark cave.
A stone room with rough walls and glowing crystals.
And in the center… a shining, floating crystal.
That was him.
What the—?! I'm a rock!
No. Not just a rock. A Dungeon Core.
He could feel it now—energy flowing through him. Magic. Power. And something else… a voice, soft and curious.
"...Are you awake, Master?"
Riku blinked. Or tried to. He didn't have eyes. Or a mouth. Or hands.
But someone was standing in front of him.
A small girl with green skin, big yellow eyes, and pointy ears. A goblin.
She smiled nervously.
"I... I found you glowing, so I brought you here. Will you become my Master?""
Riku stared at the small goblin girl. Well, he didn't really stare—he couldn't. He had no eyes. But somehow, he could still see her. She stood in a small, damp cave, smiling shyly with her sharp little teeth.
"I've never seen a glowing rock before," she said. "But… you feel warm. Like something alive."
> [New monster link formed.] [Goblin Girl has become your Dungeon Familiar.]
Dungeon Familiar? Riku thought. So… she's mine now?
> [Would you like to name your Familiar?]
Riku paused. Naming something felt… important.
How about... Fio?
> [Name accepted: Fio.]
The goblin's eyes lit up.
"Fio? That's my name now? I like it!"
Even though he didn't speak out loud, Fio could somehow hear his thoughts. Maybe that was part of being a Dungeon Core.
She sat down beside him and hugged the glowing crystal.
"I'll protect you. Even if you're just a stone… I think you're special."
Riku felt something stir in his core. Warmth. Gratitude. And for the first time since his death… purpose.
---
> [Dungeon System Activated.] [Welcome, Core #049: Riku.] [Basic functions online: Room Creation, Monster Summon, Trap Set, Mana Drain.]
A glowing screen appeared in his mind. He could feel the cave walls, the mana in the air, and the empty space around him. He didn't have hands, but he knew how to shape the world.
"Master?" Fio asked. "Are you… building something?"
He concentrated, and a square stone room formed next to them. A simple wooden door appeared at the entrance of the cave.
Fio gasped. "You can build! That's amazing!"
> [Dungeon Level: 1] [Mana: 100/100] [New Room Created: Basic Chamber]
Excitement rushed through Riku's crystal body. It was just like a strategy game! He could make rooms, set traps, summon monsters…
He wasn't stuck. He was in control.
---
Suddenly, he felt something strange. Movement. Footsteps.
> [Alert: Intruders detected.]
Three rough-looking men entered the cave. Bandits. Dirty, armed, and laughing.
"Looks like this place is empty," one said. "Let's take anything shiny."
Another pointed at Riku's crystal.
"What's that? Worth anything?"
Fio stood up, eyes wide with fear.
"N-No! Stay back!"
The bandits laughed. One of them drew a sword.
Riku felt a strange rage burn in his core.
No one hurts my familiar.
He focused.
> [Summon: Stone Spike Trap – 30 Mana] [Activate.]
The floor cracked open under the lead bandit. A sharp stone spike shot up—straight through his chest.
He died instantly.
The other two screamed in terror. Fio ducked behind Riku's crystal.
Let's make it two more, Riku thought.
> [Summon: Mud Pit – 20 Mana] [Summon: Rock Sling Trap – 20 Mana]
The ground turned to sludge beneath one bandit. He fell, sinking fast. The last man turned to run—only to be crushed by a falling boulder from the ceiling.
Silence.
> [Enemies defeated.] [Mana remaining: 30/100] [Dungeon Level increased.]
---
Fio peeked out and looked at the bodies.
"You… protected me," she whispered. "You really are my Master."
Riku felt tired, but proud. This world was dangerous. But he had power here. A strange, magical power.
And for the first time in his life…
He liked it.
The bodies of the bandits lay still on the cold stone floor. Fio crept closer, her small hands shaking.
"They're really dead…" she whispered.
She looked back at Riku's glowing crystal. "You saved me, Master. But... will more bad men come?"
Riku focused, opening his system menu.
> [Mana: 30/100]
[Room Capacity: 1/5]
[Monster Capacity: 0/3]
I need defenses. And allies.
He scanned through the summon list.
> [Available Monsters (Beginner Tier):] – Goblin (10 Mana)
– Slime (5 Mana)
– Stone Bug (8 Mana)
He had only 30 mana left. Not much. But it was enough to summon two weak monsters.
Let's start small.
> [Summon: Slime – 5 Mana]
[Summon: Goblin – 10 Mana]
---
A puddle of blue goo appeared and wobbled happily on the floor.
Fio giggled. "A slime! So squishy!"
Next, a small male goblin emerged from a glowing circle. He rubbed his eyes and looked around, confused.
"I'm… alive?" he asked. "I was dying in the forest…"
Fio ran to him. "You're in Master Riku's dungeon now! He saved you, just like he saved me."
The goblin looked at the glowing crystal, then dropped to his knees. "I'll serve you. Please, let me protect this place."
> [New Goblin Warrior joined your Dungeon.]
[Name the monster?]
Name... how about Goru?
> [Name accepted: Goru.]
The slime made a bubbly noise, like it wanted a name too.
Fine, you too. You'll be... Blobby.
> [Name accepted: Blobby.]
---
Now Riku had his first team:
Fio, the brave goblin girl
Goru, the loyal goblin warrior
Blobby, the cheerful slime
Together, they explored the next chamber. Fio helped move stones while Blobby cleaned the floor with its gooey body. Goru held a small wooden sword found on one of the bandits.
> [New Room created: Training Chamber]
[New Structure: Basic Mana Well – slowly restores mana over time]
The peaceful rhythm of the dungeon didn't last long.
That morning, as Fio trained with Goru in the new chamber, Riku felt something sharp—like a blade scraping against his soul.
> [Warning: Hostile presence approaching.]
[Number of enemies: 2]
[Class: Reaper Scout – Elite Hunter Type]
Reapers.
Riku didn't know how, but the name brought a wave of dread.
He quickly opened the dungeon system.
> [Mana: 80/100]
[Available Traps: Stone Spike (30), Mud Pit (20), Alarm Rune (10)]
[Available Summons: None – monster cap reached]
Not enough monsters. Not enough time.
But he did have traps—and his mind.
He placed a Mud Pit in the front chamber, then added Stone Spikes just beyond it. Finally, he placed an Alarm Rune at the entrance.
> [Setup complete.]
The rune flashed.
> [Alert: Enemy entered dungeon.]
---
Two Reaper Scouts in black armor stepped inside. Their faces were hidden under white bone masks. One of them knelt beside the dead bandits.
"Crude work," he hissed. "But effective."
The other turned his head toward the glowing crystal.
"It's evolving. We must destroy it now."
---
They stepped forward.
Trigger the pit.
One sank suddenly into the mud. But the other leapt over with shocking speed—straight into the Stone Spikes.
The trap pierced his armor but didn't kill him.
He pulled himself off and growled.
"Tricks? Pathetic."
---
Fio stepped in front of Riku's crystal, her small hands trembling.
"Don't touch Master!"
The Reaper laughed. "You think a goblin can stop me?"
Goru charged in from the side, sword raised.
"I'll protect Master Riku!"
The Reaper slashed his blade—but Blobby leapt up and smacked it aside with a slap of goo.
The goblin's sword stabbed into the Reaper's side.
He fell to one knee.
"Impossible…"
Fio shouted, "Now, Master!"
Riku poured all his mana into one final spike trap.
> [Summon: Piercing Spike Trap – 50 Mana]
A massive spike shot from the ceiling—straight through the Reaper's chest.
> [Enemy defeated.] [Dungeon Level increased.]
---
Only one enemy remained. He pulled himself out of the mud, growling.
But before he could move—
> [Special Event: Core Awakening reached] [Choose your next evolution.]
Three options appeared:
1. Mana Expansion Core – Double mana recovery speed
2. Summoner Core – Increase monster limit
3. Soul Core (Rare) – Begin evolving into humanoid form (locked until Level 5)
Riku paused.
He wanted to fight—but more than that, he wanted to live.
He chose Summoner Core.
> [Evolution complete. Monster cap: 6]
He quickly summoned:
> – 1 Goblin Archer
– 1 Stone Bug
– 1 Firefly Wisp
They surrounded the last Reaper and attacked together. Arrows flew, flames sparked, and stone legs stabbed.
The final Reaper screamed as his body was torn apart.
> [All enemies defeated.] [Mana: 0/150] [Dungeon Level: 3]
---
Fio cheered. "We did it!"
Goru held his bleeding arm. "Master… thank you. You saved us again."
Riku's crystal glowed brighter than ever.
---
Far away, the man in black armor frowned.
"They defeated my scouts?"
He looked at the map, where a single light was glowing in a dark forest.
"Very well. Let the Core evolve… We'll crush it when it reaches its peak."