The Silver River, The Sky of Kukai vol.7 -The Young Monk Who Crossed the Sea in Search of a Thousand Years of Hidden Knowledge-

The Seal

1. Sealing Clay

Spring had come to Mount Kōya, but the mountain was still wrapped in morning mist.

Only the sound of water flowing through the valley could be heard. On the slope opposite the temple construction, another project was moving forward in secret.

Kūkai stood at the entrance to the tunnel and slowly looked inside.

Since the hidden workshop had been discovered, Tangen’s people and Kūkai’s disciples had worked on the temple during the day. At night, guided only by small lamps, they entered the mountain.

They cut through rock, rebuilt the water channels, and repaired the old stone walls one piece at a time.

They were not building something new.

They were sealing the mountain carefully, while keeping the mineral vein alive and ensuring that the structure would remain safe for a thousand years.

Deep inside the tunnel, Tangen pressed his ear against the stone wall.

He closed his eyes and did not move for a long time.

At last, he stood and slowly shook his head.

“We stop here today.”

Kūkai turned to him in surprise.

“We still have half a day of work left.”

Tangen smiled.

“The mountain is telling us to rest.”

Without question, the disciples began putting down their tools.

But Kūkai continued looking into the tunnel.

The rock was dry.

There was less spring water than the day before.

He could see no reason to stop.

In Tang China, things had been different.

Time was limited, and neither workers nor materials were wasted.

One studied the conditions and chose the best course.

That was what Kūkai had learned from the Master as the meaning of skill.

Tangen watched Kūkai’s face.

He said nothing.

He did not criticize him.

As always, he only smiled quietly.

The next morning, the sound of hammers filled the tunnel again.

The damaged water channel was strengthened, and underground water began flowing quietly into a newly cut passage.

At the far end of the workshop, the plate marked with the mineral veins remained fixed in place.

Around it, layer after layer of stone was built up. Clay, lime, and packed earth were placed over one another.

One disciple asked,

“Do we really need to seal it this carefully?”

Kūkai was about to answer when Tangen spoke.

“We are not sealing the mountain.”

The disciples looked up.

Tangen lowered his eyes toward the underground water flowing beneath the chamber.

“We are sealing the flow.”

That was all he said before returning to the stonework.

Kūkai watched his hands in silence.

Each time a section of the wall was finished, Tangen listened to the water.

He took a handful of earth and checked its moisture.

He touched the rock and felt for the slightest movement.

After every small step forward, he stopped and checked again.

He was extremely careful.

Kūkai thought to himself,

This would be safe even without taking so much time.

He had not spoken those words to anyone.

But that small doubt had begun to enter his heart, quietly, like snowmelt flowing down the mountain in spring.

⸻

2. The Voice of the Mountain

The work was still unfinished when early summer arrived.

Inside the tunnel, there was no difference between day and night.

Only the lamps lit the stone walls, while the endless sound of falling water disappeared into the darkness.

That day, Kūkai stood before a wooden board used as a plan and gave instructions to the disciples.

“Extend the water channel half a foot to the west.”

“Raise this stone wall by one more level.”

“Add another layer around the chamber.”

The disciples began working without hesitation.

The techniques Kūkai had learned in Tang China were steadily moving the project forward.

From a short distance away, Tangen watched in silence.

As always, he said nothing.

He simply placed his hand against the tunnel wall.

He closed his eyes.

He listened to the water moving beyond the rock.

After a while, he let out a quiet breath.

“There is more water again today.”

Kūkai looked up.

Even when he listened carefully, he could hear no difference from the day before.

“Are you sure?”

Tangen only smiled.

“The mountain never shows the same face twice.”

Then he placed his hand against the wall again.

Kūkai looked toward the back of the tunnel.

The work was going well.

The water channels were nearly complete, and the sealing clay was being added according to plan.

By the calculations he had learned in Tang China, the project could be finished within ten more days.

That night, heavy rain fell.

The sound of rain striking the mountain continued deep into the tunnel.

The next morning, Kūkai prepared to restart the work.

But Tangen stood at the entrance and quietly shook his head.

“We do not enter today.”

The disciples stopped.

“It is still dangerous.”

Kūkai looked up at the sky.

The rain had already stopped.

The clouds were beginning to break apart.

Still, Kūkai tried to begin the work.

“The tunnel is dry.”

Tangen turned toward him.

There was no blame in his eyes.

Only the same gentle expression as always.

“It only looks dry.”

Kūkai stared at him.

Then he repeated the meaning silently.

The surface was clear.

But inside the mountain, the rain had not yet ended.

Tangen spoke quietly.

“A mountain moves much more slowly than a person.”

No one could answer.

The work was stopped for the day.

The disciples cared for their tools, selected the stones again, and quietly prepared for the following morning.

Kūkai stood alone at the tunnel entrance.

One more day.

Even half a day would move the work closer to completion.

That thought slowly grew inside him.

From the darkness of the tunnel came only the sound of water.

It was as if the mountain itself were trying to speak.

⸻

3. The Final Stage

At the end of summer, the cries of cicadas filled Mount Kōya.

The long work of strengthening the tunnel had finally reached its last stage.

At the deepest point, several layers of stone had been built around the ancient vessel. Outside them were layers of clay, lime, and packed earth.

The water channels now guided the underground water into new paths. Several escape routes had also been created so that too much pressure would never gather in one place.

The disciples had begun calling the whole structure a sacred barrier.

But Kūkai knew that it was more than prayer.

It was a design made to protect the mountain.

The long rain of the previous days had stopped, and the weather was now hot and humid.

That day, the final materials were brought into the tunnel.

Tangen walked through the workshop again and again, checking the stone walls.

He placed his hand against the rock.

He lowered his ear toward the floor.

He listened to the underground water.

Again and again, he checked everything.

Kūkai watched from a short distance away.

Too careful.

He could not stop himself from thinking it.

In Tang China, the work had been more practical.

Once the necessary checks were complete, people moved on to the next stage.

That was why projects could be finished quickly.

That was why great work could be done.

Tangen was different.

He moved one step forward, then stopped.

He checked again.

As if asking the mountain itself, he listened again and again.

At last, Tangen walked toward Kūkai.

“Kūkai.”

His voice was quiet.

“Only one step remains.”

Kūkai nodded.

The final task was to strengthen the stone chamber holding the mineral map with one last layer of sealing clay.

Once that was complete, the underground workshop would not be opened again for a long time.

“Let us wait three days,” Tangen said.

“Until the mountain settles.”

Kūkai asked without thinking,

“Three whole days?”

“Yes.”

“We have come this far, and now we wait another three days?”

Tangen smiled gently.

“We are protecting something for a thousand years.”

“Three days are nothing.”

The disciples nodded quietly.

But another thought had already begun to grow inside Kūkai.

Three days.

Was it truly necessary?

The clay and stone were already firm.

The water channels were complete.

The water level in the tunnel was stable.

Everything he had learned in Tang China, and all the experience he had gathered since returning, told him that the work was ready.

At sunset, the disciples finished their preparations and began descending the mountain.

Kūkai alone returned to the tunnel.

Holding up a lamp, he looked toward the stone chamber.

The stones had been placed beautifully.

The clay had been packed tightly with no gaps.

Water flowed quietly through the channels.

There was no sign of anything wrong.

Kūkai let out a small breath.

“Surely this is enough…”

No one heard him.

But those words quietly disappeared into the deepest part of the tunnel.
⸻
4. The Silent Night

That night, Mount Kōya was strangely quiet.

The cicadas that had cried through the day had fallen silent, and only the wind crossing the valley moved the tops of the cedar trees.

As planned, the work had been stopped. The disciples cleaned their tools and returned to their huts.

At the entrance to the tunnel, the stones needed for the final sealing were stacked in careful rows.

One more day.

Perhaps only half a day.

Everyone believed that would be enough.

Only Kūkai could not sleep.

Late that night, he went alone to the tunnel.

When he raised his lamp, long shadows moved across the stone walls.

He walked to the deepest part of the workshop and stopped.

The sealing work was beautiful.

The stones had been placed with perfect care. The clay had been packed tightly with no gaps, and clear water flowed quietly through the channels.

Kūkai closed his eyes and repeated the calculations in his mind.

The amount of water.

The water pressure.

The slope of the channels.

The weight on the stone walls.

Nothing was wrong.

What he had learned in Tang China and what he had learned through his own experience both gave him the same answer.

There was no need to wait until tomorrow.

Then he heard the faint sound of sandals behind him.

When he turned, Tangen was standing there.

He carried no lamp. He only watched Kūkai with the same calm expression as always.

For a while, neither of them spoke.

Only the sound of water echoed through the tunnel.

At last, Tangen looked toward the sealed chamber.

“It is well made.”

At those words, some of the tension left Kūkai’s shoulders.

“Then perhaps…”

The words escaped before he could stop them.

“Perhaps we do not need to wait three days.”

Tangen quietly shook his head.

“Is there a reason to hurry?”

Kūkai could not answer.

There was no reason.

The work could simply be finished.

And because it could be finished, he wanted to finish it.

That was all.

Tangen gently placed his hand against the rock wall.

He closed his eyes.

After a long silence, he smiled faintly.

“The mountain is still breathing.”

Leaving only those words behind, Tangen slowly walked out of the tunnel.

Kūkai remained alone in the darkness.

The flame of the lamp trembled.

Then a single drop of water fell from somewhere.

Drip.

In the silent tunnel, the sound seemed strangely loud.

Kūkai looked up.

There was no visible change in the rock.

The channels continued to carry water as before.

And yet, an uneasiness he could not explain remained inside him.

Three days later, the time for the final sealing would come.

⸻

5. The Final Seal

Only one day had passed since Tangen had said they should wait three days.

The rain from the night before had stopped, but Mount Kōya still held a great deal of water.

Drops fell from the cedar leaves and ran along the rocks. Deep inside the tunnel, underground water continued to flow without pause.

At dawn, the disciples began to gather.

They all believed the final sealing would take place two days later.

Kūkai walked alone to the deepest chamber and studied the stonework.

There were no cracks in the wall.

The channels were quietly carrying the water away.

Nothing had changed since he had inspected it the day before.

The knowledge he had gained in Tang China.

The experience he had gained at Manno Reservoir.

Everything gave him the same answer.

There was no reason to wait any longer.

The sound of sandals came from behind him.

It was Tangen.

He quietly placed his hand against the rock wall and closed his eyes.

It was the same as every other morning.

Kūkai looked at him for only a moment.

Then he turned toward the disciples.

“Take your positions.”

At Kūkai’s command, the disciples began to move.

Even after hearing those words, Tangen said nothing.

He did not try to stop them.

He only watched Kūkai in silence.

Kūkai refused to meet his eyes.

“We will begin the final stage.”

The air inside the tunnel tightened.

The disciples carried large stones through the narrow passage. Clay was spread, and the stone chamber slowly began to close.

Kūkai gave instructions for each step, then stood before the final stone himself.

He raised his right hand.

“Seal it.”

The hammer fell.

A dry sound filled the tunnel.

Another strike.

Then another.

At that moment, something deep beneath the earth gave a low groan.

Rumble…

⸻

6. The Collapse

The heavy sound rose from deep beneath the ground.

No one moved.

The hands holding the hammers stopped, and everyone in the tunnel raised their heads.

Kūkai listened.

He could still hear the water.

There was no wind.

Silence continued for a moment.

“Continue.”

At Kūkai’s words, the work began again.

The final materials were carried in.

Clay was pressed into place.

The hammers fell.

One strike.

Then another.

At that moment, the sound of bedrock splitting echoed from deep inside the tunnel.

Crack.

Then the earth itself began to twist and shake.

Countless small stones rained down from the walls, and the lamps swung wildly.

“Stop!”

Kūkai shouted.

But the roar swallowed his voice.

A scream came from farther inside.

“It is collapsing!”

“Run!”

Someone fell.

A man carrying stone was trapped beneath a fallen rock, and the others pulled desperately at his arms.

Dust filled the tunnel at once, and the lamps went out one after another.

In the darkness, only human voices could be heard.

“There are still people inside!”

“This way!”

“Help us!”

It was not one voice.

The cries came from many side tunnels, overlapping again and again.

Only then did Kūkai understand.

There were far more people inside the mine than he had realized.

Then another sound came.

It was different from the shaking earth.

Low.

Heavy.

Endless.

It sounded as though a great river deep inside the mountain had broken through a barrier.

The next moment, the water inside the channels began to turn backward.

The clear flow became muddy in an instant, and a dark flood rushed toward them from the depths of the tunnel.

Someone shouted with a trembling voice.

“Water…!”

Kūkai moved to run deeper inside.

Then a hand gently rested on his shoulder.

⸻

7. The Hidden Passage

Kūkai turned.

Tangen stood behind him, his hand still on Kūkai’s shoulder.

His expression had not changed.

He looked as calm as he had that morning.

“Tangen!”

Kūkai shouted.

But Tangen did not answer.

Still looking toward the depths of the tunnel, he gave a small nod.

At that moment, the earth groaned again.

The bedrock strained, and stones as large as fists fell from the ceiling.

Screams rose from every part of the tunnel.

“This way!”

Tangen’s powerful voice rang through the passage.

Even in the chaos, his voice reached every ear with strange clarity.

The confused workers all turned toward him.

“Take the lamps!”

“Help those who cannot walk!”

“Do not run!”

Only short commands were needed.

No one disobeyed.

Tangen walked to the side of the tunnel and placed both hands on a large stone slab.

With a heavy sound, the stone slowly moved.

Behind it appeared a narrow passage, barely wide enough for one person.

Kūkai held his breath.

“Send the injured first.”

Calmly, Tangen guided the people into the passage.

An old man entered first.

Then a stoneworker.

A young man who had been carrying earth followed, supported by others.

The disciples, though shocked, took the hands of the older workers and disappeared into the narrow opening.

All the while, the sound of the flood grew louder.

Muddy water broke over the channels and struck the rocks with great force.

A cold wind rushed through the tunnel.

The smell of earth and metal filled the air.

“Hurry!”

Someone shouted.

But the flood was faster than the voice.

Whenever someone fell, another person reached out a hand.

When a man’s leg became trapped, everyone worked together to pull him free.

No one was left behind.

Supporting an injured man by the shoulder, Kūkai looked into the narrow passage.

Walls cut directly into the rock.

A passage that turned again and again.

Thick stonework.

Beyond it lay a chamber large enough for people to gather closely together.

Kūkai drew a sharp breath.

The last person entered the chamber.

Kūkai was about to follow.

Then he looked back.

Tangen was gone.

No—

Tangen was not inside the chamber.

He was standing outside the entrance.

⸻

8. The Stone Chamber

“Tangen!”

Kūkai moved to rush out of the chamber.

But Tangen quietly raised his right hand.

That single gesture stopped Kūkai’s feet.

The sound of the flood was already close.

The whole tunnel shook, and fine drops of water began to fall from the ceiling of the chamber.

The people inside stood pressed together, holding their breath.

The disciples trembled. An injured stoneworker clenched his teeth and leaned against the wall.

No one spoke.

Tangen slowly looked around the entrance to the chamber.

Then he studied each person’s face, one by one.

His eyes stopped on Kūkai.

Kūkai could not speak.

Something inside his chest had begun to collapse.

Tangen remained where he was.

Kūkai stepped forward.

“Wait!”

His voice disappeared beneath the roar.

Tangen looked at him gently.

That was all.

Then he smiled.

It was the same smile he had worn on the day they first met at Mount Wakasugi.

There was no blame in it.

No anger.

No sadness.

Only the same calm smile.

The next moment, Tangen closed the stone door.

From the outside, he slowly dropped a thick wooden bar into place.

Thud.

The heavy sound reached deep into the chamber.

Kūkai ran to the door.

He pushed with both hands.

He threw his shoulder against it.

It did not move.

“Tangen!”

No matter how many times he shouted, there was no answer.

Beyond the door, only the sound of the flood breaking against the rocks remained.

The roar grew louder until it shook the earth itself.

Then the lamps inside the chamber went out, and darkness covered everyone.

No one could move.

Kūkai pressed his forehead against the door and struck it again and again with his fists.

Outside, rocks collapsed.

Even after the sound ended, no one inside the chamber spoke.

⸻

9. Silence

In the darkness, only the rough breathing of the people could be heard.

Then, little by little, the roar moved farther away.

The sound of falling rock faded.

The movement of the flood faded.

Everything seemed to disappear into the depths of the earth.

Only water remained.

Drip.

Drip.

Somewhere, a drop of water continued to fall.

Kūkai still stood with his forehead against the stone door.

At last, he placed both hands on it and struck it again.

Only a dull sound returned through the chamber.

Again.

And again.

The skin on his fists split, leaving red marks on the stone.

Still, Kūkai did not stop.

No one tried to stop him.

No one could.

No one knew how much time had passed.

Then one disciple whispered,

“…It has become quiet.”

The words fell into the darkness.

Kūkai slowly raised his face.

He gently placed one hand against the stone door.

It was cold.

Only that coldness passed quietly into his palm.

There was no answer.

The sound of water continued.

Kūkai closed his eyes.

In the darkness, only one image remained.

Tangen’s final smile.

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