The words came out like a vow, carried by the morning wind that blew across the overpass. No one replied, but they didn't need to. Suzune adjusted her rifle, Ichika kicked at a loose piece of asphalt, and Hana held her stuffed rabbit close. They all understood what Riku meant.

Their home was gone. Whatever was beneath the earth wasn't finished.

Riku looked toward the ruins of Nagano City, a faint plume of smoke still rising where the FamilyMart used to stand. "We move north," he said. "Toward the mountains. There's a chance the tunnels connect there. If we're right, we might find what's causing it."

Ichika frowned. "You're saying that… thing's still alive down there?"

Riku nodded grimly. "Alive, growing, maybe spreading through the old tunnels. If it's moving under us, there's a map somewhere that shows its path."

Suzune adjusted her sling. "We'll check the Disaster Management Office. It should have seismic and geological data."

"Exactly." Riku looked at her. "If it's following fault lines or old volcanic channels, we'll know."

Hana blinked up at him. "So… we're going underground?"

Riku forced a small smile. "Eventually. But not until we know what's waiting for us."

They packed quickly. A few cans of food, the last of their diesel, weapons, and a single solar battery Ichika had salvaged. The rain had eased into a mist, leaving the world slick and gray.

By noon, they reached the city center. Nagano was a dead maze of streets, flooded alleys, and toppled buildings covered in vines. The silence was suffocating.

Suzune led the way, her rifle scanning corners. Ichika carried the solar panel on her back like a strange metal shield. Hana stayed between them, clutching her rabbit in one hand and Riku's sleeve in the other.

When they reached the Prefectural Office, the main doors were jammed with debris. Riku pried one open with a crowbar, the hinges groaning like they hadn't been moved in years. Inside smelled of damp paper and mold.

"Everyone stay close," Riku ordered.

They swept the first floor, then found the Disaster Prevention Center on the second. Its glass door was locked, but Suzune knelt and picked it in less than a minute.

Inside were old computers, maps, and stacks of reports. Dust covered everything. Riku wiped a map table clean with his sleeve. "Find anything with fault lines, tunnels, or geothermal data."

Ichika checked the filing cabinets while Suzune examined a dusty server rack. She connected the solar battery and pressed a few keys. After a few flickers, one monitor lit up weakly, displaying an ancient Windows login screen.

Riku stood behind her. "Can you get in?"

"Give me a minute." Suzune typed rapidly. A few error messages flashed, then the desktop appeared. "Got it."

She navigated through folders, opening one labeled Seismic Network Logs.

On the screen, several charts appeared — tremors, fault maps, and energy readings spanning months. Suzune frowned, scrolling. "These readings are recent… three weeks ago. Small tremors along the Chikuma River, increasing near Matsushiro."

Ichika raised a brow. "That's where the old war tunnels are, right?"

Suzune nodded. "Yes. The Matsushiro Underground Headquarters — built during the war, abandoned decades ago. There are kilometers of tunnels under that mountain."

Riku's jaw tightened. "If that thing's moving under the surface, that's where it's going."

Hana tugged on his sleeve. "So… it's like a monster hiding under the mountain?"

He looked down. "Something like that."

Ichika pulled a rolled-up map from a drawer and spread it on the table. "Here. The tunnels run beneath Zōzan Park and link to several emergency exits along the ridge."

Suzune traced a line with her finger. "If it's traveling along these old lava tubes, it would follow this path north. There's an access point here — Emergency Exit Five."

"Then that's where we'll check first," Riku said. "If we're lucky, it's sealed. If not, we'll find out what's inside."

They left the city before dark, heading toward the foothills. The rain had stopped completely now, leaving a thick fog clinging to the valley.

It was quiet — too quiet. Even the wind seemed to hold its breath.

Hana broke the silence first. "Do you think people lived in those tunnels before?"

"During the war," Suzune said softly. "Soldiers built bunkers and hideouts underground. Some say they were preparing to move the government there if Tokyo fell."

Hana frowned. "That's scary."

Ichika gave a small smirk. "You'll fit right in then."

Riku shot her a look. She shrugged. "What? Humor helps."

By evening, they reached the base of the hill. The concrete entrance to the emergency tunnel was hidden behind overgrown bamboo and moss. A rusted steel door stood half-buried in mud. The white stenciled number above it — "5" — was barely visible.

Riku examined it closely. "The hinges are corroded but intact."

Suzune brushed away moss and felt the metal. "Warm."

Riku looked at her. "Hot spring lines?"

"Possibly. This whole mountain sits on geothermal channels."

He grabbed the wheel and slowly turned it. The lock resisted, then gave way with a heavy metallic click. The door groaned open, releasing a wave of damp air that smelled faintly like iron and decay.

"Stay sharp," he said, switching on his flashlight.

The tunnel was narrow, lined with old bolts and stained concrete. A soft sound echoed inside — not dripping water, but a faint hum, like the walls themselves were breathing.

Hana gripped his hand tighter. "I don't like it."

"Neither do I," Riku said.

They advanced ten meters before the floor began to slope downward. Patches of black growth clung to the ceiling — like vines, but pulsing faintly.

Ichika muttered, "That's not normal."

"Back up slowly," Riku ordered. "We go far enough to see, not to die."

Suzune stopped, crouched, and ran a hand along the wall. "This… isn't natural. It's spreading through the rock itself."

"Living stone," Ichika said dryly. "Perfect."

Riku pointed ahead. "See that turn? That's the junction. We check it, then go back."

They reached the intersection — four tunnels branching out like veins. The air vibrated softly, a rhythm too slow to be human.

Suzune placed a small sensor puck on the ground, a device she'd modified from an old motion alarm. Its light blinked red. "Movement. Southwest quadrant."

"Deeper inside," Riku said. "That matches the readings near Matsushiro."

Hana looked pale. "It's breathing again."

Riku nodded grimly. "And it's heading north — right toward us."

They retreated carefully, closing the heavy steel door behind them. Outside, the air felt lighter but colder.

"We can't kill what we can't see," Ichika said. "So what's next?"

Riku glanced at Suzune. "You said these tunnels connect to the old hot spring lines, right?"

"Yes. The onsen used to use geothermal water pumped through here."

"Then maybe we can use it," he said. "If we open the upper valve, we can flood the tunnels with mineral water. It's heavy, full of calcium and iron — maybe it'll choke the growth."

Suzune considered it. "You want to drown it."

"I want to slow it down," Riku said. "Buy us time."

Ichika sighed. "This is officially the dumbest brilliant plan I've heard. Fine. Where's the valve?"

"Zōzan Park," Suzune said, checking the map. "A small maintenance shack above the tunnels."

"Then that's our next stop."

They climbed the slope as night fell. The wind howled through the trees, carrying the faint scent of sulfur. The park was deserted — rusted playground equipment, stone walls cracked by roots, and a small metal shed at the top.

Suzune pried open the door. Inside, a maze of rusted pipes and pressure gauges lined the walls. The labels were faded, but still readable.

She crouched and examined the main valve. "Still pressurized. The spring's active."

"Can it handle being forced open?" Riku asked.

"Once. Maybe twice. After that, it'll blow."

"Once is all we need."

She turned the wheel slowly. The pipes creaked, then shuddered. A deep rumble rolled under their feet, and steam hissed from the vents.

Hana covered her ears. "It's shaking!"

Riku steadied her. "Hold on."

From somewhere below, a dull roar echoed — the sound of rushing water pouring into the old tunnels.

Suzune's voice was steady. "Flow diverted. It's flooding the lower sections."

They waited, watching the gauges tremble. Then, silence.

Ichika peered out the doorway. "So… did it work?"

"Only one way to find out," Riku said.

They returned to the tunnel entrance. Steam poured out through the cracks. Riku opened the door just enough to peek inside.

The walls glistened white — coated with thick mineral deposits that hardened as they watched. The black growth beneath it twitched, then stilled.

"It's calcifying," Suzune said. "The minerals are binding it."

Riku shut the door again. "Then we seal it."

Together, they turned the wheel until the lock clicked back into place. Riku drove a metal bar through the handle and welded it shut with the torch attachment from their stove. The smell of burnt metal filled the air.

Ichika exhaled. "So… it's dead?"

"Not dead," Riku said. "But trapped."

Suzune nodded. "At least for now."

Hana hugged her rabbit. "Then… we really ended it?"

Riku looked at her tired eyes — eyes that had seen too much for her age. "Not yet," he said softly. "But we're getting closer."

They set up camp on the hill overlooking the valley. The night air was cool and clean, the stars faint through the haze. Suzune boiled water and made tea from dried leaves, their first warm drink in days.

Ichika leaned back against her pack. "You know, if this was a movie, this would be the part where the monster bursts out again."

Riku gave a tired smirk. "Let's not give it ideas."

Hana sat by the small fire, feeding it bits of paper and watching the smoke spiral up. "When it's really gone," she asked, "what do we do then?"

Riku thought for a moment. "We rebuild. Find others. Maybe even plant something again."

Hana smiled faintly. "Like flowers?"

"Yeah," he said. "Flowers."

For the first time in months, the air felt still — not the tense kind of silence that warned of danger, but the calm that came when the world finally stopped shaking.

Suzune poured the tea into small tin cups and passed them around. "To surviving another day."

Ichika raised hers. "And to not dying in a tunnel."

Hana giggled and clinked her cup against theirs. "To warm corners."

They drank quietly as the wind carried the faint scent of rain from the valley below.

For the first time since the refinery, Riku allowed himself to believe they'd won a small victory. Maybe not the last one they'd need — but enough to keep moving.

And as he looked out over the dark valley, where the earth had stopped breathing for now, he whispered to himself,

"This isn't over. But it's a start."

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