Leon reached home long past midnight.
The small apartment felt colder than usual. The lights in the living room were dim, and the air carried the faint smell of medicines. He slipped off his shoes quietly, trying not to wake anyone.
But a soft voice came from the kitchen.
"Brother…? Is that you?"
His little sister, Lia, stepped out. Eighteen years old, tired eyes, but still forcing a smile as always. She worked part-time after classes, doing her best to support the family.
Leon's chest tightened.
After facing a monster… facing his sister felt harder.
"Yeah," he said softly. "It's me."
Lia frowned. "Why are your clothes dirty? Did something happen?"
Leon hesitated.
He couldn't tell her the truth. Not yet.
"Just… slipped on the road. Nothing serious."
Lia sighed in relief. "Don't scare me like that. Mom's sleeping. She had a bad coughing fit earlier."
Leon's heart sank.
Their mother's illness was getting worse. Hospitals demanded money he didn't have. Medicine prices kept rising. And Leon's jobs barely covered rent and food.
That was his reality… until today.
A faint blue glow blinked in the corner of his vision — the System reminding him it existed.
Lia went back to her room. "Sleep, brother. You look exhausted."
"Yeah. You too."
Once she left, Leon sat alone on the sofa.
His hands trembled—not from fear, but from excitement mixed with confusion. The System notification hovered before him:
New Skill Unlocked: Vein Sense (Basic)
Effect: Detect lifeforms and energy within a short radius.
Leon whispered, "Vein Sense… activate."
The world shifted.
He gasped as blue lines spread across the room, like glowing trails of energy. Every living thing had its own "vein signature." He could sense:
— His sister's calm, warm aura
— His mother's weak, flickering presence
— And… something else
Leon's eyes widened.
Just outside the apartment building…
Something crawled on the walls.
Something with a twisted, unstable blue signature.
A monster.
His heart slammed against his chest.
"Damn it… it followed me."
He stood up, fists clenched. This wasn't just a tutorial anymore. The System wasn't a game—real lives were at risk.
He walked to the window.
A dark creature with long limbs clung to the building's outer wall. Its head jerked unnaturally as it sniffed the air, searching.
Leon felt rage rise inside him.
If this monster reached his mother's room…
or his sister's…
He wouldn't let it happen.
The System flashed again:
Urgent Quest: Eliminate the Intruder
Reward: Stat Increase + New Skill
Penalty: Monster will attack nearby lifeforms
Leon took a deep breath.
"Fine. If this is the path the Infinite Veins want me to walk…"
His veins began to glow faintly, blue light pulsing under his skin.
"…then I'll walk it."
He opened the window silently and stepped onto the fire escape, eyes locked on the monster.
For the first time in his life, Leon wasn't running away.
He was hunting.