Arin didn't sleep that night.
He tried.
He lay on his back, staring at the ceiling of his small room, watching shadows move as the moonlight shifted through the window.
Every time he closed his eyes—
He saw it again.
F Rank.
The letters were burned into his mind.
He turned to his side.
"…Error Detection," he muttered.
The words still felt strange in his mouth.
Useless.
That's what everyone called it.
And honestly… it sounded useless.
He let out a slow breath and sat up.
"Then what was that?"
That screen.
That message.
[ERROR DETECTED]
That wasn't normal.
That wasn't part of the ceremony.
At least… he didn't think it was.
Arin swung his legs off the bed and stood up.
His room was small. Just a bed, a table, and a cracked mirror on the wall.
Nothing had changed.
Everything felt the same.
Except him.
"…If it's real, it should happen again."
He didn't know why he believed that.
But it made sense in his head.
Abilities weren't supposed to activate once and disappear.
Right?
"…Okay."
He took a breath.
"Error Detection."
Nothing happened.
He frowned.
"Do I have to… focus or something?"
He closed his eyes.
Tried to think back to that moment in the alley.
The feeling.
The confusion.
The question he asked—
What does this even mean?
For a few seconds, there was nothing.
Then—
A faint flicker.
Arin's eyes snapped open.
"There—"
The screen appeared again.
Small.
Unstable.
Like it didn't fully belong in this world.
His heart started beating faster.
"It's real…"
The words formed slowly this time, like they were struggling to exist.
[NO ACTIVE ERROR FOUND]
"…Huh?"
That was it?
Arin stared at the screen.
"That's it?"
He waved his hand through it.
Nothing.
No reaction.
"…So it only shows something when there's an error?"
He paused.
Thinking.
Then looked around his room.
The table.
The wall.
The mirror—
The screen flickered.
Arin froze.
"…Wait."
He stepped closer to the mirror.
It was old. The surface slightly warped. A crack running from the top corner down to the middle.
The screen reacted again.
[MINOR STRUCTURAL FLAW DETECTED]
Arin blinked.
"…You're kidding."
He reached out and touched the crack.
The screen flickered once more, highlighting it faintly.
"…It shows… flaws?"
Not just big things.
Small things too.
He leaned back slightly, his mind starting to race.
"Okay… okay…"
If that was true—
Then this ability wasn't just "seeing errors."
It was seeing what was wrong.
With anything.
"…Then why did it say system inconsistency yesterday?"
His expression slowly changed.
That wasn't a crack in a mirror.
That was something much bigger.
Something he probably shouldn't even be thinking about.
"…Forget that for now."
He shook his head.
One step at a time.
First—
He needed to understand this ability properly.
---
The next morning, the city was still buzzing.
Not as intense as yesterday, but the excitement hadn't died down.
Guild banners were still up.
Recruiters still walking around.
Newly ranked people already moving in groups.
Arin walked through the streets quietly.
No one looked at him.
Or if they did, they didn't care.
Which was better than yesterday.
He stopped near a training ground.
A few newly ranked adventurers were practicing.
Swords clashed.
Magic flashed.
People laughed.
Normal.
Strong.
Everything he wasn't.
Arin stood at the edge, watching.
"…Let's test this."
He focused.
Tried to activate the ability again.
A few seconds passed.
Then—
The screen appeared.
Faint.
He looked at one of the fighters—a tall guy swinging a sword confidently.
The screen flickered.
[STANCE IMBALANCE DETECTED]
Arin blinked.
"…What?"
He looked closer.
The guy's movements were fast, aggressive—but slightly off.
His footing.
Too forward.
Too exposed.
"…That's a flaw?"
He shifted his gaze to another person.
A mage, casting fire magic.
The screen flickered again.
[MANA WASTE DETECTED]
"…No way."
Arin's eyes widened slightly.
He kept looking.
One person.
Then another.
Every time—
Something appeared.
Small flaws.
Hidden inefficiencies.
Mistakes no one else seemed to notice.
"…This…"
His grip tightened slightly.
"…this isn't useless."
It wasn't flashy.
It wouldn't win fights directly.
But—
If he could see what was wrong—
Then he could fix it.
And if he could fix it—
Then—
"Hey."
A voice cut through his thoughts.
Arin turned.
One of the guys from the training group was looking at him.
"Why are you staring?"
"…Sorry," Arin said quickly. "I was just watching."
The guy looked him up and down.
Then frowned.
"Wait… weren't you the F-rank from yesterday?"
There it was.
Arin didn't respond.
The guy smirked.
"Yeah, I remember now. 'Error Detection,' right?"
A few others turned to look.
"…What does that even do?" someone asked.
"Probably tells him how useless he is," another said, laughing.
A few chuckles followed.
Not loud.
But enough.
Arin felt that familiar tightness in his chest again.
But this time—
It didn't stay.
He exhaled slowly.
"…It shows flaws."
The words came out before he could stop them.
The group paused.
"Flaws?" the guy repeated.
"Yeah," Arin said, looking at him directly now.
"Like how your stance is too forward."
Silence.
For a second—
No one spoke.
Then the guy laughed.
"Are you serious?"
Arin didn't smile.
"If someone attacks your left side, you won't recover in time."
The laughter stopped.
Just slightly.
"…You're talking a lot for an F-rank."
"Maybe," Arin said.
"But I'm not wrong."
The guy's expression hardened.
"Then show me."
Arin hesitated.
He didn't have a weapon.
Didn't know how to fight.
But—
"…Fine."
He stepped forward.
Slowly.
Carefully.
"I'm not going to fight you," he said.
"I'll just point it out."
The guy scoffed.
"Do whatever you want."
Arin watched him closely.
Focused.
The screen flickered.
[STANCE IMBALANCE DETECTED]
"…Move your right foot back," Arin said.
The guy didn't move.
"Why would I listen to you?"
"Because right now, you're off-balance."
A pause.
Then—
Reluctantly—
The guy adjusted slightly.
Arin's eyes narrowed.
The screen flickered again.
The message changed.
[STANCE STABILIZED]
"…See?" Arin said quietly.
The guy froze.
"…What?"
"Try swinging now."
He did.
The movement was smoother.
More controlled.
Even he could feel it.
"…That's—"
He stopped.
The others were watching now.
Not laughing.
Not talking.
Just… watching.
Arin stepped back.
"…That's all."
Silence filled the space.
Different from yesterday.
This time—
It wasn't mocking.
It was uncertain.
Confused.
"…Do it again," someone said.
Arin shook his head.
"I'm not your trainer."
He turned.
And started walking away.
"Hey—wait!"
He didn't stop.
Because for the first time since the ceremony—
Something felt different.
Not big.
Not overwhelming.
But real.
"…It works."
His ability wasn't useless.
Not even close.
And if that was true—
Then maybe—
Just maybe—
Everything else they said about him…
Was wrong too.