Night had already settled by the time Tanjiro and Giyu stepped into the cracked concrete tunnel that led beneath the city. A faint, damp smell of moss mixed with something heavier, something rotten, drifting through the air. Tanjiro recognized it instantly.
A demon's scent.
The deeper they walked, the louder the constant drip of water grew, echoing through the maze of narrow passages. The city's underground waterways were old and forgotten, a labyrinth carved beneath streets that no longer remembered their names.
Giyu moved forward silently, the faint glow of emergency lights reflecting off his dark hair. Tanjiro followed, his senses sharp.
"Giyu," Tanjiro said quietly, "the scent is getting stronger. And it feels… strange."
"That is him," Giyu replied. "Lower Moon Two. The demon is called Soyar. Muzan created him recently. Some say he was a martial artist when he was alive. His ability is troublesome, so be careful."
Tanjiro nodded. "Right."
Their footsteps continued. Water pooled along the ground, swirling around their ankles. Pipes rattled overhead with the sound of shifting pressure.
Everything felt tense. Like a breath held too long.
Then…
Tanjiro stopped.
"Giyu… did we pass this place already?"
Giyu turned his head slightly. "No. We came from the opposite direction."
Tanjiro frowned. "But the scent mark I left earlier… it's on that wall."
Giyu's eyes narrowed. "Then it has started."
The passage trembled with a faint, mocking laughter.
It came from everywhere. It came from nowhere.
A voice slid through the tunnels, thin and slippery.
"So you noticed. Not bad. Not bad at all."
Tanjiro whipped around, searching for the source. But the air churned with the same smell in all directions.
Soyar's voice echoed again.
"You two are lost already. Your sight is lying. Your hearing is lying. Even your sense of touch will betray you. Every one of your senses will turn against you."
Tanjiro gritted his teeth. "A five senses manipulation technique."
Giyu exhaled slowly. "He twists the direction each sense perceives. If you think something is behind you, it is probably not. If you hear something on the right, it may be left or below. The more you move, the more lost you become."
The laughter grew louder.
"You understand well, Water Hashira. I admire that. Perhaps I should let you wander for a century."
Tanjiro took one step forward.
His foot landed on nothing.
For a moment the world spun. The tunnel floor shifted. Gravity tilted. Water flowed sideways.
Tanjiro stumbled and caught himself, breathing hard.
"Tanjiro!" Giyu called out.
Except Giyu's voice came from above. And behind. And in front.
All at once.
Tanjiro steadied himself.
"This scent… this vibration… the direction is wrong."
Soyar whispered again.
"Not wrong. Correct. This is the way your body should feel. You humans rely far too much on your senses. Let me teach you how fragile they truly are."
The tunnel twisted again in Tanjiro's vision. The walls looked curved, and the floor rippled like liquid metal.
Giyu vanished from sight.
Tanjiro felt his heart tighten. "Giyu!"
No response.
Only dripping water. Only the demon's laughter.
Tanjiro clenched his fists.
"If he controls my senses… then I cannot rely on them. I need to break the space itself."
He raised his blade.
"Water Breathing… Seventh Form."
The demon's laughter halted for the briefest moment.
Tanjiro swung.
"Drop Ripple Thrust!"
The waterway exploded from the force, concrete cracking, water spraying out into the empty air.
The explosion of air pressure pushed back the false directions. Hidden vibrations shifted. A shape moved… fast.
Tanjiro sensed it.
Not from scent. Not from sound.
But from the faint tremor in the demon's breath.
He charged.
"Your trick works only when you stay close to your target. You were hiding right beside me."
A gasp came from the darkness.
"How did you…?"
Tanjiro's blade flashed.
He cut through the confusion.
He cut through the false world.
He cut through Soyar.
The demon screamed as his upper body split.
Tanjiro landed lightly on the cracked floor, breathing hard but steady.
Soyar trembled, trying to regenerate. His eyes widened when he saw Tanjiro watching calmly.
"You… monster. How… how did you find me?"
Tanjiro answered in a gentle voice that still carried iron.
"You cannot hide your fear. Even a demon breathes when they panic. And your breath trembled."
Soyar shrieked.
"No. No. I cannot die here. Muzan will not tolerate this. I need to escape. I need to—"
Tanjiro swung once more.
Soyar's head dropped to the ground.
The body crumbled to ash seconds later, fading into the water's misty air.
The underground maze slowly returned to normal. The scent and sounds aligned again, like a world put back into place.
Tanjiro scanned the area.
"Giyu!"
A faint splash answered him. Tanjiro sprinted deeper and found Giyu leaning against a broken pipe, blinking.
Giyu groaned softly. "My head feels… strange."
"Soyar's ability trapped our senses. But he is gone now." Tanjiro offered his hand.
Giyu took it.
Once he stood up, he gave Tanjiro a long look, his eyes filled with quiet respect.
"You saved me."
Tanjiro smiled. "We are in this together."
Giyu nodded slowly, then exhaled.
"The next demon will be stronger. And after that, even stronger. But you handled this one with ease."
Tanjiro tightened his grip on his sword.
"Because we cannot allow anyone to suffer again. I will defeat every demon. No matter how strong. No matter how many."
Giyu gave a faint smirk.
"Good. Then let us move. The next target waits."
Together they walked into the darkness again.
And the waterway behind them fell silent.