The Kamogawa Delta Cipher | Chapter 1: The Kamogawa Delta in May

The Kamogawa River in May makes people let their guard down.

The breeze along the river is gentle, students sit on the grass, spreading out convenience store bags and laughing. On the stepping stones, tourists were taking photos while waiting for their turn.

The town of Kyoto has always been made of 'water'.

Mio Amamiya sometimes remembers her father's voice saying that.

Every time she looks at the river.

Mio looked up from her paperback book.

On the opposite bank, a small cheer went up.

"What's that?"

"Did someone draw that?"

"It's not very photogenic."

It sounded like the voices of high school girls.

Mio inserted her bookmark and stood up from the bench.

A crowd had formed near the center of the stepping stones.

As she approached, she saw white lines drawn on the surface of the stone.

It was strange for graffiti.

Geometric. A mix of straight lines and curves. And, it was strangely well-proportioned.

There was a man pointing his smartphone at it.

"Let's film this for TikTok."

Beside him, a female foreign tourist tilted her head in wonder.

Mio stared at the stone.

Three white lines.

A semicircle.

A diagonal line.

A dot.

That was all.

Yet, there was a strange sense of unease.

"Do you know this?"

A voice came from behind.

Turning around, she saw Yuma Sakaki standing there.

He held a plastic bottle of sparkling water in one hand.

"You've got that thinking face again."

"Not really."

"No, you do. Definitely."

Yuma stepped down onto the jumping stones.

"What is this? Art?"

Mio did not answer.

She crouched down at the edge of the stone.

She traced the lines with her fingertip.

It wasn't chalk.

It's close to paint.

Moreover, it hasn't completely faded even though it's wet.

"...It looks like a surveying symbol."

"Surveying?"

"A mark used in old river construction work and the like."

Yuma's eyebrows twitched slightly.

He is in the Department of Civil Engineering.

He reacts to words like that.

"But it's a bit strange."

"What is?"

"The location."

Mio stood up and looked around.

The Kamogawa Delta.

The place where the Kamo River and the Takano River meet.

It is a land that has suffered repeated flood damage since long ago.

That is why the people of Kyoto are sensitive to water levels.

"This stone is usually a bit more underwater."

Yuma looked at the river.

"Yeah, there hasn't been much rain until yesterday, after all."

"But is there any point in drawing it in a position that can only be seen today?"

Yuma did not reply.

Instead, he took out his smartphone and snapped a photo.

"This is going on social media."

"Don't."

"Too late."

He showed her the screen.

It had already been posted.

#KamogawaDeltaCipher

The view count had already exceeded five thousand in just a few dozen minutes.

Mio let out a small sigh.

Kyoto looks like a closed-off city.

But in reality, it is the opposite.

Tourists.

International students.

Videos.

Social media.

It is constantly changing shape due to information flowing in from the outside.

It is just like the river.

"Amamiya-san?"

Suddenly, someone spoke to me in English from the side.

I turned around to see a blond young man standing there.

I had seen his face at the university before.

“...Louis?”

“I knew it. We’re in the same archaeology class, right?”

He was a French exchange student.

His Japanese was quite fluent.

Louis pointed at the stepping stones.

“This is interesting, isn’t it?”

“Is it?”

“Yes. Especially this shape.”

He zoomed in on his smartphone screen.

“I’ve seen a similar symbol in France.”

Mio’s gaze froze.

“Where?”

“In the blueprints for an old canal facility.”

Yuma chimed in.

“A canal?”

“Yes. From the nineteenth century.”

Mio looked at the stepping stones once more.

The wind blows.

The surface of the river ripples.

The white lines appeared slightly distorted by the reflection of the water.

It was at that moment.

Something clicked in Mio's mind.

Canal.

Surveying symbol.

Water level.

Kyoto.

“...No way.”

“Huh?”

“This might not be a game.”

Yuma laughed.

“It’s started. Detective mode.”

Mio ignored him.

She checked the position of the stones.

The stepping stones are not in a perfect straight line.

They are placed with subtle shifts.

I once wondered about that.

Why aren't they lined up evenly?

But now, another possibility crossed my mind.

What if this...

is not just a set of stepping stones,

but 'coordinates indicating something'?

That night.

Mio had returned to her apartment near the university.

A single six-tatami mat room.

An old wooden building.

When she opened the window, she could hear the sound of an ambulance in the distance.

On her desk were a laptop and a stack of documents.

A copy of an old map of Kyoto was taped to the wall.

Mio zoomed in on the photo from earlier that day.

Tracing the symbols.

Rotating.

Flipping.

But the meaning remained elusive.

Her smartphone vibrated.

It was from Yuma.

[It's already hit 100,000 views]

Followed by a URL.

A video streamer had started an on-site investigation.

In the comment section,

"A treasure map?"

"Theory about an underground passage"

"Kyoto is too scary"

were lined up.

Mio closed the screen.

Then, she suddenly cast her gaze toward the edge of the desk.

An old college notebook was lying there.

It belonged to her father.

A personal effect returned from his laboratory after he went missing.

She had read it over and over again.

It was full of incomprehensible entries.

But recently, she had begun to understand a little.

Her father had been investigating the "underground waterways of Kyoto."

Mio opened the notebook.

She turned the page.

Water level observation.

Canal.

Underground cavity.

Inside it, there is one word circled in red.

—Delta.

Mio's finger stopped.

At that moment.

Her smartphone vibrated again.

This time, it was a private number.

After a few seconds of hesitation, she answered the call.

Silence.

Only noise could be heard.

A rushing sound, like the sound of water.

“...Hello?”

There was no reply.

But faintly, the sound of a man's breathing was mixed in.

And then.

A low voice.

“...Don't look.”

The call was disconnected.

The room fell silent.

Outside the window, the wind was swaying.

Mio did not move for a while.

Before long, she turned her eyes back to the photograph on the desk.

The stepping stones of the Kamogawa Delta.

The white symbol.

And her father's notebook.

It was too perfect to be a coincidence.

Mio opened her laptop.

A map of Kyoto's rivers.

A map of the Meiji-era Kamogawa river improvements.

A map of the Lake Biwa Canal route.

She lined them up on the screen one after another.

Outside, the Kamogawa River in May was flowing quietly.

As if pretending to know nothing at all.