The night air felt heavy as Kai made his way back toward the city. Every step burned. His wounds had closed, but deep inside, something wasn't right. His veins pulsed with heat — not normal warmth, but something unstable, wild. The aftereffects of the dungeon's boss still lingered inside him.
"Damn it," he muttered, clutching his chest. His heartbeat was fast, erratic, like something was clawing inside.
The road stretched quiet and long, the moon glowing faintly over the rooftops. When he finally reached the gates, the guards barely glanced his way — adventurers returned half-dead all the time. He was no exception.
By the time he entered the guild building, his body was shaking. His vision blurred again. The moment he took a step inside, his knees buckled.
"Kai!"
He barely heard the voice before everything went dark.
---
When he opened his eyes, he was lying on a soft bed. The scent of herbs filled the room. He blinked a few times and saw a familiar face hovering over him. Lira — the nurse.
She looked tired, but relief washed over her face the moment his eyes opened. "You idiot," she said softly, pressing a hand to his forehead. "You went into a medium-rank dungeon alone?"
Kai tried to laugh, but it came out as a groan. "Wanted to test my strength."
Lira frowned. "You're lucky to even be alive. You've got a damaged mana core, and your internal energy flow is unstable. What were you thinking?"
Kai stared at her for a moment, then smiled weakly. "That I could handle it."
She sighed. "You adventurers are all the same."
Lira dipped a cloth into a bowl of shimmering liquid and placed it on his chest. The cold sensation made him flinch, but soon it turned warm, spreading through his body like calm waves.
"What is that?" he asked.
"Mana stabilizer," she said, gently rubbing his arm. "It'll help your energy flow return to normal. But you still need rest — a few days at least."
Kai leaned back, closing his eyes. "Rest, huh? You make it sound easy."
Lira gave him a small smile. "I know people like you don't rest. You keep fighting until you break."
Kai turned his head toward her, his eyes meeting hers. "And people like you keep putting us back together."
For a moment, the air between them grew quiet. Lira's cheeks flushed slightly, and she turned away, pretending to adjust the potion bottles beside the bed. "You talk too much," she said under her breath.
Kai chuckled, even though it hurt. "Maybe."
She placed another glowing charm on his chest, murmuring a soft incantation. As she did, Kai could feel the wild heat inside him slowly settling — like a storm beginning to calm. But then, something strange happened.
The charm glowed red instead of blue.
Lira's eyes widened. "That's… not right."
Before she could react, Kai's body jerked violently. His veins lit up with crimson light, his mana flaring uncontrollably. The air in the room grew hot, and small sparks of flame burst from his palms.
"Lira—" Kai gasped, clutching the bed. "It's burning—inside me—"
"Hold still!" Lira's voice was sharp now. She pressed both hands to his chest, pouring her mana into him. "Your core is rejecting the stabilizer!"
The flames flared brighter, licking the edge of the sheets. Lira cursed under her breath, then grabbed a vial from the shelf — a glowing green potion — and poured it over his chest. The flames hissed, the red glow faded, and slowly, Kai's body began to cool.
After a few tense moments, his breathing steadied. Lira exhaled, sweat dripping down her temple.
Kai blinked weakly. "That… was fun," he joked, trying to smile.
She glared at him. "You almost exploded!"
"Would've gone out in style," he murmured, grinning faintly.
Lira smacked his arm. "Idiot."
Then her expression softened. She sat beside him and sighed. "Whatever you absorbed in that dungeon… it's not normal mana. It's corrupted. It's fused with your own energy now, and your body doesn't know how to handle it."
Kai looked down at his hand. Faint red lines still glowed under his skin, pulsing softly. "Can it be fixed?"
"Maybe," Lira said quietly. "But it'll take time. You'll need to learn to control it — bend it, not fight it. If you can't, it'll tear you apart from the inside."
Kai chuckled weakly. "Guess that means training again."
"Not yet," she said quickly. "You're in no condition for that. Promise me you won't enter another dungeon until I say so."
Kai smirked. "You sound like Gladis."
"I mean it," she said, her tone firm. "You're not indestructible, Kai."
He looked at her, seeing the worry in her eyes. For a moment, the silence was heavy. Then he nodded. "Alright. I promise."
Lira relaxed slightly and stood. "Good. I'll prepare another stabilizing spell. Try to sleep."
But Kai didn't sleep. Not yet. As the room dimmed and the sound of her footsteps faded, he stared at his glowing hand again. Deep down, he could feel it — the power inside him wasn't just dangerous. It was… alive.
It whispered in his mind, faint but clear.
"Use me."
Kai's heart skipped. "What the hell…"
He sat up slightly, holding his breath. But the voice was gone.
The next morning, Lira returned to check on him. She brought food, medicine, and another charm. Kai looked better — color had returned to his skin, and his strength seemed to be coming back.
"You look less like death," she said with a teasing smile.
Kai smirked. "Guess I'm a fast learner."
She sat beside him, her tone turning serious. "Listen, Kai. The corrupted mana… it's volatile. But if you can master it, it might become your strongest weapon. It's rare — dangerous, but powerful."
"Figures the system wouldn't give me something easy," Kai said.
She nodded. "There's an old training chamber below the guild. Hardly anyone uses it. If you want, I can take you there once you're stable. You'll need control before your next dungeon run."
Kai smiled. "Deal."
Lira started to pack up her tools, but paused when she noticed him still staring at her. "What?" she asked.
"Nothing," Kai said with a small grin. "Just… thanks."
"For saving your reckless self again?"
"Yeah," he said quietly. "And for caring."
Lira rolled her eyes but smiled faintly. "Don't get used to it."
She turned to leave, and as the door closed behind her, Kai finally leaned back, closing his eyes. The system suddenly chimed in his head again.
(Ding!)
> New System Task: "Master the Fire Within"
Objective: Control the corrupted mana without external aid.
Time Limit: 7 Days
Reward: New Skill – Infernal Surge
Failure: Mana Core Collapse
Kai exhaled slowly. "Of course. A deadline."
He looked out the window at the rising sun. The city was already waking up — adventurers marching to their next dungeon, merchants opening their stalls, and the guild banners fluttering in the wind.
"Seven days," he whispered. "Alright then… challenge accepted."
His hand glowed faintly again, that crimson light pulsing with quiet heat. But this time, Kai didn't fight it. He just stared at it — and smiled.
---
That night, when he finally slept, his dreams were strange. He saw the Crimson Caverns again — the boss he'd slain, the molten core, and the fiery energy that had sunk into his chest.
In the dream, he stood before a shadowy version of himself, eyes burning red, surrounded by flame.
"You think you can control me?" the shadow said with a grin.
Kai clenched his fists. "I don't need to control you. I'll make you part of me."
The shadow laughed. "We'll see."
And with that, Kai woke up — drenched in sweat, heart racing. The air around him shimmered faintly with heat.
He looked down at his hands again. The faint red glow pulsed like a heartbeat.
He smiled to himself and whispered, "Day one."