After slipping past the Observers’ patrol, the two of them pressed deeper into the dark.
The tunnel plunged toward the depths of the earth. The air was frigid and tasted of iron. Traces of old lamps dotted the walls, as if the breath of miners long gone still clung to the stone. With every step, the damp mud sucked at the soles of their boots, muffling their pace. Asahi extinguished the torch and gave Koyoi’s shoulder a light tap as a signal.
From deeper in the cavern came a low, approaching drone of machinery. A deep vibration traveled through the ground into the soles of their feet, resonating within their very chests. Koyoi gripped her charm pouch and whispered "Be still" to the Wind God. The wind spread around them like a thin membrane, swallowing the sound of their breathing. Though the darkness was thick, a faint, pale blue light bled through it—the mechanical glow of the Observers.
When they finally reached the deepest point, the tunnel suddenly opened into a colossal cavern.
A dome-shaped void stretched out before them. Limestone pillars hung from the ceiling, their surfaces flickering with light whenever a stray droplet fell. The ground beneath them was treacherous with jagged, fallen rock, yet the very center of the hollow was unnaturally flat, as if someone had meticulously carved the earth away.
The air here was bone-dry. The dampness of the tunnels had vanished as if it were a lie, replaced by the stinging scent of metal and oil. Koyoi could feel it—the underground air had been warped by the sheer heat of the machines.
"...What is this?"
Koyoi caught her breath. A massive apparatus had been erected in the center of the hollow. It must have been over ten meters tall—a tower of black metal. Countless pipes sprouted from it, stabbing deep into the ground.
Around these pipes, circular rails spiraled, and small, unmanned carts sped along them. The carts were transporting pale blue crystals, feeding them into the base of the tower. Koyoi instinctively felt that if she touched them, they would be warm. Shards of the Earth Pulse. They were burning the very life of the land.
Complex, code-like engravings were etched into the tower’s surface, occasionally flashing with a rhythmic red light. The heartbeat of the mountain was being forcibly rewritten into the pulse of a machine. Koyoi gritted her teeth.
The core of the tower glowed with a sickly blue-white light. In time with that radiance, a heavy, low-frequency thrum echoed through the chamber. The sound wasn't steady; it ebbed and flowed, pulsing like the heartbeat of a creature in agony. The stone floor vibrated so intensely that dust drifted upward, hovering in the air. The earth itself was being pulled toward the engine.
Feeling the direction of the vibrations through her feet, Koyoi imagined the flow of the Earth Pulse being sucked into the tower. A cold terror washed over her—the fear of the mountain turning into a hollow shell. If the ground grew thin, the towns and forests above would collapse. They weren't just stealing the lives of the Gods; they were shaving away the foundation of everything that lived on this land.
"They're... siphoning the Earth Pulse," Asahi groaned. "They mean to strip the energy of this entire mountain down to the roots."
Dozens of Observers swarmed around the construct. They moved busily, recording data and operating levers. It resembled a vast underground factory. White floodlights cut across the cavern, casting the Observers' long, distorted shadows against the walls. No one spoke. Their only signals were short hand gestures; their movements were devoid of any wasted effort. They didn't seem like humans—they seemed like cogs in a mechanism. The soullessness of it made Koyoi’s skin crawl.
Asahi peered out from behind a crag, biting his lip. "There are too many of them. If we make a scene here, we’ll be surrounded."
Koyoi nodded, her fingers sliding over her pouch. She could feel the Wind God trembling inside, terrified by the stifling underground air.
Asahi traced a small circle on the floor with his finger, indicating a path. If they circled around to the back of the tower, there was a spot that would be momentarily hidden from the Observers' sight. Koyoi followed his movement with her eyes, tracing the route in her mind. If they failed, it would end here.
"...What about the Gods?" Koyoi whispered, searching for their presence.
She couldn't feel any individual auras like the Wind God or the Waterway God. Instead, she heard the scream of the earth itself. It wasn't a sound for the ears, but a voice felt in the bones. From the depths of the mountain, a plea of "It hurts" shook the "light" within her chest. Koyoi closed her eyes and loosened the drawstring of her pouch. The Wind God let out a tiny breath, overlapping with the cry of the Earth Pulse.
Within that scream, she thought she heard a short name. Tsuchimori. Hatamori. The names carved into the wooden tablets of the shrine.
"...The Earth God’s kin are here too," Koyoi murmured, pressing her palm to her chest. The names she had sworn not to forget were suffering right here.
Asahi nodded, glaring at the tower from the shadows.
“...It hurts.” “...Stop.”
Countless tiny spirits were being sucked into the pipes, vanishing as they turned into light. The device was fueled by the lives of the Gods. Each spirit was a flickering spark, gathered like a swarm of insects. Even as they tried to flee, they were ensnared by an invisible net. Koyoi clenched her fists until her nails dug into her palms.
Pressing her ear to the wall, she heard a different kind of groan. It wasn't the machine; it was the sound of rock grinding against rock. The Earth Pulse was being torn apart. Koyoi winced, unable to bear the phantom pain. The Wind God curled up inside the pouch, shivering. The wind couldn't flow here. A place where the wind couldn't pass was a place where life couldn't breathe.
"I won't let them get away with this," Asahi whispered, his hand tightening on his sword. "I'm going to smash that thing to pieces."
"But there are too many of them."
"We'll take them by surprise. If I cut the largest pipe, it should trigger a meltdown."
Asahi started to lunge forward from the shadows, but Koyoi grabbed his sleeve and shook her head.
"Wait. I want to see if the wind can reach it."
She let a thin stream of air flow from the mouth of her pouch. The wind glided across the floor toward the tower, but it was blocked halfway by a faint, transparent wall. There was a barrier around the core structure. Every time the wind touched it, a blue spark flickered for an instant.
"There's a barrier..."
Asahi clicked his tongue. "Then I'll have to be the one to cut through it. Use the wind to disrupt the machine and blind them."
Koyoi nodded, focusing her mind on the light in her chest. If they hesitated here, the Earth Pulse would wither.
"Once we get close, I'll draw the guards away," Asahi said shortly. Koyoi looked at his back and could only nod. She was afraid. But beyond that fear, there was someone she wanted to save.
Koyoi took a breath and dropped to one knee. Pressing her palms together as if in prayer, she whispered to the Wind God, "Let’s do this together." The Wind God’s trembling subsided slightly, and the pouch grew warm.
Gripping the pouch, Koyoi remembered the light in her chest—the small flame that had flickered to life at the start of her journey and guided her here. If that light went out now, the voices of all the Gods she had saved until today would vanish too. She relaxed her shoulders and steadied her breathing.
At that moment—
"Intruders detected."
A cold, mechanical command rang out through the cavern. The air turned brittle in an instant. Every Observer looked up simultaneously, their hollow gazes snapping toward the shadows. A floodlight stabbed through the dark, leaving their shadows nowhere to hide. The ceiling lights flared to life all at once, making the cavern daylight-bright.
"Damn it...!"
The Observers closed in. A high-pitched alarm bell rang out, and the machine's rotation accelerated. The pipes vibrated violently, and the floor began to heave. There was no escape. Koyoi hugged her pouch, praying to the Wind God to protect them.
Then, from behind the machine, a massive shadow emerged.
It was a beast-shaped automaton clad in heavy metal armor. Its red eyes glowed as it bared its fangs. The crest engraved on its chest pulsed in the same rhythm as the machine's light. The power core. Koyoi stared at the light, feeling a chill run down her spine.
The grit at her feet shuddered as the Guardian’s roar echoed through the hollow. Koyoi swallowed hard and gripped her pouch tight. Her fingertips shook, her breath grew shallow, and her heart hammered against her ribs. Cold sweat broke out on her back, and the loose gravel beneath her vibrated further. A ringing sound filled her ears.
"A Guardian!"
Asahi stepped in front of Koyoi, shielding her.
The battle had begun.