Light swallowed them whole.
For a moment, there was nothing—no sound, no sensation, no ground.
Then—
CLACK-CLACK. CLACK-CLACK.
The rhythmic rumbling of wheels.
Warm air.
A faint smell of old wood.
Seungho blinked hard, eyes adjusting to a dim, flickering lantern glow. He looked around—rows of wooden seats, sliding paper doors, patterned curtains.
An old-fashioned train.
Jisung sat beside him, equally dazed, blinking like a confused owl.
"Hyung," he whispered, "are we… in a period drama?"
"No," Seungho muttered. "We're in trouble."
Everyone else in the train car was asleep—slumped over, breathing softly. The only noise was the steady heartbeat of the train tracks beneath them.
"This is… too quiet," Seungho said.
"Maybe we're ghosts."
Before Seungho could respond—
POP!
A glowing blue panel exploded right above their heads.
Jisung screamed; Seungho only flinched violently inside.
The system screen spun dramatically, before stopping:
"SYSTEM NOTICE: Welcome to MUGEN TRAIN INSTANCE."
Another line formed:
"Main Quest: Defeat LOWER MOON ONE – ENMU""Reward: 5 Years Swordsmanship Experience"
Jisung was the first to react.
"HYUNG, IT'S REAL! IT'S ACTUALLY REAL!" he shouted, grabbing Seungho's shoulders and shaking him.
Seungho stared, horrified.
"Lower Moon ONE?! On our FIRST world? With THESE bodies?!"
Jisung suddenly froze.
"Wait… doesn't Enmu kill people with dreams? Sleep? Hypnosis?… Something like that?"
"Yes," Seungho said flatly. "He literally murders people in their sleep. And we—" he gestured at their completely average limbs, "—don't even have stamina to walk up stairs without dying."
Jisung gulped.
"Well… uh… plot twist?"
Seungho buried his face in his hands.
Next to their feet were two neat sheaths. Two swords rested quietly.
Jisung grinned, picked one up, and immediately dropped it because it was too heavy.
"I can't even hold this properly!"
Seungho lifted his, trying to copy a posture he vaguely remembered from anime.
His wrist trembled.
"We are supposed to assist Tanjiro… with THIS? We can't even protect ourselves."
"Wait, look!" Jisung pointed. "There's more on the screen!"
The system flashed two tiny icons:
"Status Effect: NEWBIE PROTECTION – Cannot be hurt physically or mentally (Temporary).""Status Effect: LANGUAGE PACK – Japanese language unlocked (Temporary).""Note: These are LIMITED buffs. Don't expect more."
Jisung cheered, raising his sword shakily.
"We're INVINCIBLE!"
"That second skill doesn't even help in fighting… and why does the system talk like it's fed up with us?"
"No idea, but I'm READY!" Jisung announced, posing dramatically. "Bring it on, demons!"
Seungho sighed. "We're on the Mugen Train arc. So Enmu will appear. That's… bad."
"Bro, what are Enmu's powers again?"
"He puts people into dreams and kills them."
Jisung nodded. "Yep. Doesn't sound fun. Okay. Not questioning life choices. Let's move."
They stood up and looked at their reflections in a small mirror near the door.
Their breaths caught.
Black Demon Slayer uniforms. Haori vests. Sheathed swords. Their real faces—just younger.
"Hyung," Jisung whispered, "we're… demon slayers."
"That's not reassuring," Seungho said.
Below the main quest, something flickered:
"Quest 2: LOCKED – Requirements undisclosed"
"There's ANOTHER quest?" Jisung said. "Oh yeah, isn't there supposed to be a strong demon later in this arc too?"
Seungho groaned. "Yeah. What a drag."
They pushed open the sliding door to the next cabin.
Instantly, the atmosphere thickened.
A man with blazing yellow-and-red hair was holding a small girl by the neck—without harming her, just immobilizing. His eyes were sharp, flame-like.
"Kyojuro Rengoku," Seungho whispered.
"Wait—STOP!" Jisung grabbed Seungho's sleeve. "Plot moment!"
"That girl was the traitor! She tried to kill him," Jisung said quickly. "He's fine. He's the Flame Hashira."
Ahead of Rengoku, a boy in a green checkered haori was shaking sleeping passengers desperately.
"Tanjiro," Seungho murmured.
"That's the main character!" Jisung whispered excitedly. "Let's go!"
But before they moved, four children jerked awake, eyes blank and unfocused. They pointed makeshift weapons—screwdrivers sharpened with desperation—straight at Tanjiro.
In an instant, Tanjiro spun and struck the back of each child's neck with the dull side of his blade.
They collapsed gently, unharmed.
He exhaled—a short sigh of relief—and then noticed the two unfamiliar boys standing there like they had walked in on the wrong class.
Tanjiro blinked.
"Um… who are you?"
Jisung smiled awkwardly and bowed way too low.
"Hi! I'm Jisung! And this is Seungho!"
Seungho hit his forehead with his palm.
"Why are you introducing us NOW?"
"We have to follow him! We're supposed to assist him!"
Tanjiro blinked again.
"There were other demon slayers assigned to this train…?"
Before Jisung could brag or lie, Tanjiro stiffened.
His eyes sharpened.
"…I smell a demon's scent. Above."
Without another word, he sprinted toward the end of the car, leaped, and climbed onto the roof with practiced ease.
Jisung pointed after him.
"Follow him!"
Seungho groaned but ran anyway.
"Why are we doing this?!"
"Because QUEST REWARD, HYUNG!"
They reached the back door, climbed out, and clung to the edge as the wind blasted their faces like an industrial fan.
Tanjiro landed on top of the train.
Jisung and Seungho scrambled after him, wobbling dangerously.
"THIS IS SO MUCH SCARIER THAN THE ANIME!" Jisung yelled over the wind.
"Focus!" Seungho snapped.
At the far end of the roof, a pale figure stood—hands open, smile gentle and wrong. His coat fluttered unnaturally. His eyes glowed with soft insanity.
Lower Moon One.
Enmu.
He raised a hand gracefully, like a host welcoming guests.
"Oh my… three people managed to break through my demon blood art?"
His smile widened, elegant and terrifying.
"How troublesome."
Jisung gulped.
Seungho tightened his shaking grip on the sword.
And somewhere behind them, the system chimed softly—
"BOSS FIGHT INITIATED: LOWER MOON ONE – ENMU"
The real nightmare had just begun.