Blue light continued to seep out from the cracks in the ground. Chen Hao took a step forward, his foot landing on a loose stone slab with a cracking sound.

He didn't stop.

The three people behind him didn't move either.

The creature lay at the end of the passage, its six legs dangling to one side. Its red eyes were no longer lit, and the blue light on its shell flickered intermittently, like a light bulb about to run out of power.

"Is it dead?" Karl asked in a low voice.

"I don't know," Chen Hao said, turning around, "but at least it won't move now."

Susan held the protective bag, her fingers still pressed against the crystal's surface. The thing quieted down, no longer flashing violently, but simply brightening and dimming steadily, like breathing.

Nana leaned against the stone pillar, the red light on her right arm flashing. She raised her left arm, the green light at the tip of the guide stick so faint it was almost invisible.

“Scan… complete.” Her voice trailed off. “Nervous system… interrupted. Only…basic reflexes remain.”

“That means it’s ruined.” Karl breathed a sigh of relief. “That was quite a powerful blow.”

"Don't relax." Chen Hao stared at the circular doorway ahead. "Just because the door is open doesn't mean it's safe inside."

The light curtain in the center of the portal was still pulsating, like a reflection ruffled by the wind on water. The air near it was somewhat distorted, and the outer layer of the protective suit began to heat up.

“You can’t get through,” Susan said. “If you just walk straight through, you’ll be roasted alive.”

"Then don't go in a straight line." Chen Hao squatted down and placed his palm on the ground. "Remember the rhythm from before?"

"Three short and two long?" Karl asked.

Yes. It listens to that.

Susan looked down at the crystal in her arms: "You mean, use it again?"

“It’s not about using it,” Chen Hao said. “It’s about imitating it. It’s not afraid of light, it’s afraid of frequency.”

He turned to Karl: "Are there any capacitors left?"

Carl rummaged through his toolbox and pulled out the last battery: "That's all I have. Not enough for a second strong pulse."

"No need to put it in." Chen Hao took the battery. "We just need a light."

He connected the battery to the port on the protective bag, but didn't power it on; he just connected the circuit. Then he slapped the ground—three short slaps and two long slaps.

The ground shook slightly.

The light screen flickered and a crack appeared.

"Let's go!" Chen Hao stood up. "One by one, stand against the wall!"

Susan went first. Holding the protective bag, she bent down and squeezed through the gap, her clothes brushing against the edge of the light screen, emitting a wisp of white smoke.

"It hurts!" she gritted her teeth.

"Bear with it." Chen Hao followed.

The second person was Karl. He had just taken a step when his foot slipped, and when he braced himself with his hand, he touched the edge of a crack. His fingertips immediately turned black, as if he had been burned.

"Damn it!" He pulled his hand back. "This ground is poisonous!"

"Don't touch the ground." Chen Hao reached out and pulled him. "Hurry up."

Karl crawled over. Nana was last. She dragged her right arm, moving slowly, the guide stick leaving a shallow mark on the ground.

The light curtain began to close.

"Nana!" Susan called out.

Nana sped up and squeezed in at the last moment, her shoulder brushing against the light barrier, and a piece of her armor instantly melted away.

All four of them passed through.

Suddenly, everything became clear.

The cavern was extremely high, surrounded by smooth black rock walls. A massive spherical structure, emitting a ghostly blue light, floated in the center. There were no supports, no connecting wires; it simply hung suspended in mid-air.

"That's the core?" Karl gasped for breath.

“It should be.” Chen Hao stared at it. “It’s even brighter than in the file photo.”

“Don’t get close,” Nana suddenly said. “There’s a repulsive force field.”

As soon as she finished speaking, the shield on her left shoulder automatically deployed, then exploded with a "bang," scattering metal fragments all over the ground.

"What's going on?" Karl took a step back.

“I tried to access the analysis system,” Nana said in a low voice, “which triggered a backlash.”

"That means it's shy around strangers." Chen Hao stroked his chin. "We need to make it feel like we're one of our own."

"How do we recognize it?" Susan asked.

“Frequency.” Chen Hao looked at the crystal. “That creature was synchronized with it. Let’s try using the same rhythm.”

“The risk is considerable,” Carl said. “What if it doesn’t identify the signal, but instead attacks the intruder directly?”

"Do you have a better idea?" Chen Hao said, "How about we lie here and wait for it to invite us to dinner?"

No one responded.

Chen Hao took two steps forward.

The repulsive field reacted immediately, and a force slammed into him. He felt a tightness in his chest and almost knelt down.

“Eighteen seconds at a time,” he said. “The intervals are about the same, just now and this time.”

"You counted them?" Susan asked.

"Nonsense, how can you hide if you don't count?"

He stepped back and steadied himself.

"Five seconds before the next impact, Susan lightly touches the ground with the crystal to signal us. We rush up during the gap in the force field's recovery and stop five meters away from it. Let's see how it reacts."

“What if it just explodes?” Carl said.

"Then let's just blow it up," Chen Hao shrugged. "Anyway, we didn't bring an umbrella."

Susan rolled her eyes: "Can't you say something auspicious?"

"To be honest," Chen Hao grinned, "surviving is a bonus; escaping death is the norm."

“You’re such a happy-go-lucky idiot,” Carl muttered.

"Otherwise what?" Chen Hao said, "Beg it to let us go while we're crying?"

The plan was set.

They waited for eighteen seconds.

The air trembled slightly, the repulsive force field was released again, and blue ripples spread out from the core surface, leaving a charred mark as they swept across the ground.

The ripples receded.

"Make your move!" Chen Hao ordered.

Susan crouched down and gently touched the ground with the crystal—three short touches and two long touches.

The core paused for a moment.

The rotational speed decreased.

A ring of runes appeared on the surface, like a chain being untied.

“It works!” Karl whispered.

"Let's go!" Chen Hao led the way.

The four of them moved swiftly along the ground, stopping just before the next wave of impact, only five meters away from the core.

The temperature here was noticeably high, making breathing difficult. Their protective suits alarmed for energy overload, but they didn't take them off.

“It didn’t push us anymore.” Susan looked up. “Does that mean… it passed verification?”

"Not necessarily." Chen Hao stared at the runes. "It might just be a different method of killing."

Nana leaned against the rock wall, the indicator light on her right arm still glowing red. She accessed the residual database, comparing the crystal frequency with the core fluctuations.

“The match is…78%,” she said. “It’s just a little short of being fully synchronized.”

“Just a little bit off is just a little bit off,” Carl said. “You can’t gamble on things like failing an exam by one point or tripping while running by one step.”

“So let’s not gamble,” Chen Hao said. “Let’s try one more time, with some added ingredients.”

"Add what?" Susan asked.

"Keep the rhythm the same, but increase the signal strength." Chen Hao looked at Karl. "Connect the battery and light up the crystal, but don't turn it on fully."

Carl did as instructed. The circuit was connected, the crystal's brightness increased, and the blue light became soft yet not glaring.

"Get ready," Chen Hao said. "Wait for the next wave of attacks to end."

Time passes.

It will arrive in eighteen seconds.

Repulsive ripples diffuse and disperse.

Susan touched the ground again, and at the same time Carl pressed the switch, injecting current into the crystal.

A flash of blue light.

The runes on the core surface rotated faster, then stopped.

The entire cavern was silent for a second.

Then, the core slowly sank half a meter, the outer aura narrowed, and the repulsive force field disappeared.

"It...accepted?" Susan couldn't believe it.

"Or they might be observing," Chen Hao said, not letting his guard down. "Don't get too close."

He moved forward half a step without encountering any resistance.

"Can we get in?"

"There's no rush if we can get in." Chen Hao turned around. "Nana, can we still take data?"

Nana nodded: "Barely. There are abnormal fluctuations inside the core. It's not in a natural state."

“What do you mean?” Carl asked.

“Someone tampered with it,” Chen Hao said. “Or it malfunctioned on its own.”

"So what's our task?" Susan asked. "Fix it? Reboot it? Or shut it down?"

"Let's figure out what it's trying to do first." Chen Hao stared at the ball of light. "If it wants to explode, we'll help it untangle the wires; if it wants to live, we'll recharge it."

“You make it sound simple,” Karl said with a wry smile. “But it’s the core of a planet, not an electric car.”

“They’re essentially the same,” Chen Hao said. “They’re both batteries, except this one takes three hundred years to charge.”

Susan couldn't help but laugh out loud: "Can't you be serious for once?"

“I’m being very serious,” Chen Hao said. “I’m just explaining it in a way that I can understand.”

Nana suddenly raised her hand: "Warning. Internal energy accumulation detected, rising periodically. If this continues... it may trigger a chain reaction."

"How long?" Chen Hao asked.

"Unable to be precise. Fastest... forty minutes."

"That means there's no time to dawdle." Chen Hao looked at the three of them. "Any objections?"

No one spoke.

“Let’s get started.” He stepped forward. “Susan, take the crystal. Carl, check the backup circuit. Nana, continue monitoring the frequency changes. Let’s take it one step at a time, don’t rush.”

The four regrouped and slowly approached the core.

At a distance of three meters, runes reappeared on the core surface, but this time there was no repulsion; they simply rotated slowly, as if reading information.

“It’s scanning us,” Nana said.

"Let it sweep." Chen Hao stood still. "We didn't steal its electricity."

After the rune completed a full rotation, the sphere of light trembled slightly, then opened a crack, revealing a deeper blue light from within.

"The door is open," Susan whispered.

“It’s not a door,” Chen Hao said, squinting. “It’s an interface.”

He reached out and slowly approached.

Just as my fingertips were about to touch the edge of the gap—

Nana suddenly shouted, "Don't touch it!"

Chen Hao froze.

“Internal energy imbalance.” Nana’s speech quickened. “Contact could trigger a reverse conduction, and you’ll be drained dry.”

"Oh." Chen Hao withdrew his hand. "Then I won't touch it."

“We need to stabilize it first,” Susan said. “Use a crystal sync and slowly adjust the frequency.”

“The problem is,” Carl looked at the interface, “how do we get in?”

“It’s cracked open,” Chen Hao said. “That means it wants something.”

What do you want?

“The key.” Chen Hao looked at the crystal in Susan’s arms, “but it needs a complete signal, and we only have a 70% match right now.”

“Then let’s find a way to get it to ten,” Susan said. “We can’t just sit here and wait.”

“There’s a way.” Nana pulled up the data stream. “If we add the battery energy to the crystal and combine it with the rhythm input, we might be able to reach the critical synchronization value.”

“There’s only one battery,” Carl reminded him. “Once it’s used, there’s no backup.”

"I never planned to leave any way out," Chen Hao said. "Either we fix it or we blow it up together."

Susan took a deep breath: "Then let's give it a shot."

She untied the protective bag and held the crystal in her hands.

The blue light shone on the faces of the four people.

Chen Hao raised his hand, palm down.

“Let’s wait for the next ley line tremor,” he said. “We’ll do it together.”

The rock cavity was quiet.

In the distance, a familiar rhythm came from the ground—three short beats followed by two long beats.

Chen Hao's hand slowly fell.