Thank you so much for euphoricimage who's helped me beta this story!

Also, checkout my alternative account on Ao3 (Tuntunaa) for fanarts of On The Flip Side! :))

Edit: I should've mentioned that Sada Abe, Ishida Shou and the unnamed demon at the last scene are my OCs.


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An otherworldly beautiful young woman.

That was the first thing Sada Abe thought when he caught sight of her in the street. Porcelain skin, long black hair tied with an artful butterfly, purple eyes as charming as wisteria, and a serene, lovely smile on her face. Her unusual attire made her even more memorable, with a snow white cloak draped over her shoulder and striking knee-length skirt. A little breeze, and more of her smooth legs would be revealed. Truly a novelty, he thought, licking his lips.

Abe left the stall and followed her from a distance, carefully keeping an eye on his surroundings for black-garbed men. It would be his last night here; he couldn't stand the constant surveillance after a few days staying in this town. He had been warned by countless stall owners not to cause trouble if he wanted to live.

"Or the demon will eat you," an old man had whispered to him on his first night here. Abe had laughed at him, but the inn owner, the merchants, and every local he subsequently encountered had said the exact same thing. He thought they would be more wary of the local Kozakura clan than some fictitious demon. Hell, he had even heard little kids singing merrily about a demon eating troublemakers!

"Especially these days, young man," a stall owner had warned him. "People have been going missing in the past month. Seems like the demon was starving, as it has eaten more than usual. Rather indiscriminately too. Stay out of trouble if you don't want the demon to eat you."

Demon, demon, demon. What a load of bullshit.

Abe chugged down more alcohol, ignoring the stares from his surroundings. Being drunk wasn't a crime. It wasn't like the demon would suddenly come to eat him in the middle of a dense crowd like this. And that young woman was going towards the inn he was staying at. What, was the demon going to barge into his room too?

Abe went after her, waving half-heartedly at the inn owner. Smiled, when he saw that the woman's room was next to his. The night was young; the inn was pretty much empty as most guests had left to enjoy nightlife. He approached her in the hallway as she was about to enter her room.

"Isn't it chilly tonight, miss?" Abe hummed, gaining her attention. His gaze trailed down to the exposed skin of her legs. "I'm feeling rather cold myself. Why don't we help warm each other up?"

The woman paused, blinking at him. His heart soared when she smiled at him—

Before she turned around and continued walking, ignoring him completely.

"Is that a silent invitation?" Undeterred, Abe rushed to grab her hand, grinning. "Don't be so cold, sweetie, or I'll truly freeze."

She stared at him mutely, no longer smiling. Abe tightened his hold on her wrist as his other hand rose to brush her smooth cheek.

"What do you say, hmm? I can warm you up tonight."

"... Please let me go."

"So you can speak! For a moment, I thought you were mute," Abe smirked as he closed in on her. His hand began to move down towards her tantalising legs. "I can help you practice your vocal cords. Screaming in ecstasy all night long until you finally lose your vo—aaaaAAAAHH!"

Abe screamed because suddenly, a demon towered behind her.

It was tall and heavily built, with long, spiky dark hair and a sharp horn on the left side of its forehead. Hanafuda earrings dangled on his pointed ears. Veins bulged on its face as its mouth snarled threateningly, revealing razor-sharp fangs. Its inhuman slitted eyes gleamed blood-red, glaring at him with the intent to kill.

His pants turning wet, Abe scrambled to run for his life. Stumbling into the inn lobby, he yelled for help, alerting the inn owner and the passersby near the inn.

"A demon! It's a demon!" Abe ran outside, sobbing. Spotting a group of swordsmen garbed in black, he rushed and fell down to his knees in front of them. "Help me! There's a demon in the inn!"

The swordsmen tensed. The leader of the group unsheathed his sword. "Where?!"

"I-It's inside. It's gonna eat me!" Abe wailed.

The leader barged into the inn, followed by his men. A part of Abe thought it was strange that these people didn't question his sanity and took his claim seriously. Was that even a real demon? It could've been a figment of his drunken imagination after hearing about demons for days.

Scared shitless but curious, Abe followed the swordsmen back into the inn. Over the shoulders of the swordsmen, he caught sight of the butterfly woman in the dark hallway. No demon was seen, but a little boy was hiding behind her legs.

Where did that monster go?

"... You. You have a sword," the leader of the swordsmen said warily. "I have never seen you before. State your business in this town, swordswoman."

It took Abe a moment to realise what it meant. His eyes widened as he scanned the woman whom he had just courted. He had noticed her pretty face, her modest sized chest, her short skirt and her smooth calves, but for some reason he hadn't registered the rather conspicuous katana on her hip.

His jaw dropped even more when he heard her reply.

"My name is Tsuyuri Kanao," the woman replied calmly and bowed. "I am part of the Demon Slayer Corps. I was dispatched here to investigate the disappearance of several people in Ueda."

"The Demon what?!" Abe couldn't help but blurt out.

"A Demon Slayer…" The swordsmen also gasped.

Abe turned to look at them in horror when they sheathed their swords in unison.

"My apologies for the rudeness!" The leader bowed sharply, followed by his men. "I am Ishida Shou of the Kozakura clan. We were the ones who had sent the request. We have been waiting for you."

Abe could only stumble dazedly as he was pushed aside by the swordsmen so that the leader could guide her outside.

"Please follow us, ma'am," Ishida Shou ushered her. "The situation is dire. We have to go—"

"You should take him too, mister," a new, young voice interjected.

All eyes turned to face the boy who had been standing behind the woman. Abe stared at him in confusion. He had spiky dark hair, a scar on the left side of his forehead, red eyes and hanafuda earrings.

The boy with such familiar features pointed a clawed finger at Abe.

"He's a molester," the boy accused. "He was trying to touch my K—my older sister."

Abe spluttered.

"I'm not—Wait!" Abe pointed a shaky finger at the boy in return. "You are the demon!"

The swordsmen, unfortunately, chose to eye him suspiciously instead of the demon.

"You…" one of the swordsmen frowned at him. "You are Sada Abe."

"How did you—" Abe shrieked when the swordsmen suddenly grabbed his arms. They didn't budge when he struggled to escape, dragging him along with them. "W-what are you doing?! The demon is over there! Let me go!"

"We've received reports of an outsider harassing women for the past few days," Shou scowled, pushing Abe roughly. "This town is within our jurisdiction. Take him to the Kozakura estate. I will personally escort Tsuyuri Kanao-sama to that mansion."

Abe wailed in distress throughout his journey to the Kozakura estate.

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Kanao noticed the way the Kozakura member kept throwing glances at Tanjirou.

"... Is he your younger brother, ma'am?" Shou finally asked once they had passed the crowded street towards the outskirts. "It will be dangerous for a young child to be involved in this."

The tiny hand in hers tightened the grip. Tanjirou looked up with pleading eyes and shook his head mutely. Kanao blinked, because his behaviour now was such a contrast to how he had threatened that strange man just a few moments ago.

"He will be fine," Kanao told Shou before changing the subject. "Tell me the details."

Shou nodded. "Over thirty people have gone missing in the past month, most of them suspected to have disappeared into an abandoned mansion south of the town. Eyewitnesses claimed that some of the victims were snatched quickly by large figures at night, while others were drawn by the sounds of tsuzumi from the mansion even during the day."

"Why are you convinced that it is a demon's doing?"

"No one who entered the mansion came back out alive," Shou explained. "Just recently, a victim managed to escape the mansion, but he passed away shortly after we found him. His body was full of bite and claw marks, and he mentioned 'monsters' in his dying breath."

Kanao hummed in thought. Just like the Numa-oni, it seemed like it was a demon who was also able to establish its own domain.

Soon after, the pathways revealed a clearing with a decrepit mansion at its center. Eerie silence permeated the area as if it was hiding ominous tragedies behind its doors. Kanao furrowed her brows at the thick demonic mist that seeped through the openings of the mansion, puzzled by the swirling mixture of colours. There were lighter tones of red, purple and blue amidst the predominantly dark green mist, indicating three additional, far weaker demons residing in the mansion. Cohabitants?

It didn't matter.

Kanao turned to Shou. "When did the last victim disappear?"

"Five days ago," he said, gritting his teeth. "It was actually our Clan Head. He voluntarily went inside to rescue our Young Master, who went missing the previous night. We sent the request for aid to the Demon Slayers Corps immediately afterwards."

Kanao sighed. The night was young, and there was a possibility that the demons would make another move tonight. It was rather strange that the Demon Slayer Corps hadn't caught a rumour about these many people going missing earlier.

"You should have notified us long before thirty people had disappeared."

"... Our sincerest apologies. We thought we could handle the situation ourselves, but this demon proved to be too much. Even for our Master," Shou said regretfully, before blinking. "Ah, I forgot. One of our men thinks he saw a colleague of yours yesterday, so I guess he was the last one who had gone missing."

Kanao paused. "Another Demon Slayer?"

"Yes. Though he barged into the mansion without even notifying us of his arrival. Not sure if our member saw it right, but he said that Demon Slayer had the head of a boar and swung around two katanas while being half-naked, screaming the entire time."

"Ah… Yes, I know him," Kanao hummed, recalling the loud boar-headed man claiming to be the strongest King of the Forest and insistently pestering her for a duel. "Though, it seems like he has not managed to come back out of the mansion."

"I do not dare to hope," Shou sighed in sorrow before bowing to her. "While it might be too much to ask, I implore you to please save our Master and Young Master, Demon Slayer."

Kanao smiled at him silently before tugging Tanjirou's hand to enter the mansion together.

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Tanjirou hated the smell of this mansion.

It was horrible and tantalising and rotten and mouth-wateringly delicious. The hallway was clean and well-maintained, but a strange odour permeated the whole place. Tanjirou put his bamboo muzzle back on and desperately covered his nose with his free hand, yet it barely helped ease the smell that assaulted his senses.

"Tanjirou-san. I can't hold my sword properly."

Tanjirou blinked and looked down at her face. Kanao blinked back, before raising their joined hands.

"Hand," she said. "I can't fight while holding your hand. You can stand behind me instead."

Tanjirou frowned. He let go of her hand reluctantly, though he chose to ignore her second order and moved to stand in front of her.

"... Tanjirou-san, you're blocking my view."

Tanjirou looked back and scowled. It's dangerous. I have to protect you.

"Yes, but I'll end up cutting you if you stand in front of me," Kanao smiled. "Stand behind me."

He pouted. She sighed.

"I am not saying this to shield you from harm. You can protect my back from behind."

Tanjirou blinked, before brightening. Obediently, he moved to stand behind her—

Pong!

—Before the sharp beat of a tsuzumi echoed in his ears and Kanao disappeared before his eyes.

Tanjirou gasped, blood running cold—

Pong!

Pong!

Pong!

Pong!

The room shifted rapidly, following the beats of the tsuzumi. The hallway was gone, replaced by a tatami room, then a storage room, a double volume room, a wooden room, a long tatami room—

Pong!

And lastly, a brightly-lit double volume hall.

Tanjirou whirled around, eyes scanning his surroundings. The room was ten times bigger than the first room they had been in moments ago. The foul smell of the demons was stronger now, as if he was abruptly transported deeper into the mansion. Kanao had been standing in front of him just a few seconds ago, but now she was nowhere to be seen.

She was gone. Again.

Tanjirou shook his head. No, she was still alive. She was still here. Faint as it was, he could still smell her scent. Kanao had told him that she was strong, and he had seen her fight. She was fine. She must be fine.

He sniffed the air once before rushing to slam open the shouji doors on his right. A dark hallway greeted him. Following her scent, he ran down the hall until he found a wooden door on his left. He opened it, only to be met with another bizarrely large empty room.

It didn't take him long to realise that this mansion was much bigger than it looked from the outside.

Tanjirou gritted his teeth and opened the door at the opposite side of the room. Another hallway. He turned left, right, left. Another door. Another empty room.

He exited the room. Another hallway. Another door. Another empty room—

Pong!

His eyes widened. The room changed again. Her scent was now farther away.

Tanjirou ran to the nearest door. Another hallway. Another door. Another empty room.

Another one.

Another one.

Another one—

Pong!

And the room shifted again.

Tanjirou glared at the ceiling. It was that sound of tsuzumi. Everytime it beat, the room changed. He was transported somewhere else and so were the inhabitants of this mansion, including Kanao and the demons. Like a maze that shifted abruptly at random times, it trapped anyone who entered the mansion.

Tanjirou ran. Another door. Another hallway. Another empty room—

Pong!

The room shifted just before he entered, and all of sudden he saw a demon standing on all fours at the other end of the room.

"Hmm?" The demon tilted his head at him, his four eyes widening. His long tongue lolled out from his mouth, wriggling in agitation. "Another demon?"

Tanjirou narrowed his eyes as a pungent smell of old blood reached his nose. Judging by the scent, it wasn't the demon who created this mansion. But it was one that had lived here for a long time, devouring a considerable number of trapped humans.

"Tch. This mansion is full already. We already had a new demon come into this place just a few days ago, and now we have another one," the demon tsked, displeased. "I haven't eaten for a few days already because that newcomer stole my latest prey, so fuck off!"

The demon tensed before a long tongue shot out from his mouth, aiming for Tanjirou's neck. Tanjirou leaned sideways to dodge before grabbing the tongue and yanking it. The demon, not expecting a strong retaliation, soared towards him before a bone-breaking kick sent him flying through the shouji doors, tearing off his tongue in the process.

Tanjirou clenched the wriggling remains of the tongue in his hand, crushing it to dust. The tongue demon was a man-eating monster reeking blood of its helpless victims. He had destroyed lives and broken families apart. He had killed innocents in sadistic glee. Just like that man.

Snarling, Tanjirou lunged—

Pong!

—Before the demon disappeared following the beat of the tsuzumi.

Tanjirou froze and sniffed the air. The tongue demon had been teleported towards the opposite side, not too far off the room he was in. He turned to chase after the demon, but a new scent entered his range. It was close, closer than the tongue demon. Faint but fresh… and delicious.

It was the scent of a living human.

Tanjirou furrowed his brows. Shou had mentioned another Demon Slayer who entered the mansion yesterday. Was this the Demon Slayer? But they felt too young and weak, thick of exhaustion and fear—

And they were surrounded by the scent of another demon.

Dread filled him. Tanjirou sprinted towards the door on his left and made a beeline for those scents. Vaguely, he sensed the tongue demon rushing after him, going towards the same direction as the human scent. He had to get there quickly. Save Shigeru before the demons could get to him. Before that man could kill him.

Soon, he found the right shouji doors and barged in—

Shi—ng!

—Before jerking downwards in reflex when a blade swung towards his neck.

Tanjirou shot forward and tackled the attacker. They tumbled down the tatami floor, struggling against each other. He attempted to disarm the opponent, but a kick to his chest knocked the breath out of him, sending him flying.

Tanjirou skidded on the floor before turning to face the new enemy.

It was a demon with two red horns on his forehead and long spiky black hair fluttering on his back. His clothes were tattered in some places and stained with foul blood. Yellow-slitted pupils on red sclera glared at him and his mouth twisted into a snarl, revealing deadly fangs.

But what struck Tanjirou the most was the sword in his hands. The man in front of him smelled of a demon, but the serrated indigo blade unmistakably smelled of the sun. Just like Kanao's sword.

It was a demon… wielding a demon-slaying sword.

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Thank you for reading!