Lin Xian never expected to find such a massive military base beneath the Sea Rock Prison when they discovered the nuclear submarine's underwater secret harbor.

"No wonder the Sanctum Organization chose this place as their hideout. With a military base this size, it makes perfect sense," KIKI said with sudden realization.

"If the Sanctum Organization had prepared to ambush us in advance, how did this place fall?" Ning Jing frowned. "Or has this stronghold already been destroyed?"

"Very likely," Lin Xian replied gravely. "But when I examined the zombies in the prison earlier, none seemed to belong to the Sanctum Organization. This suggests they didn't occupy this place for long—they must have arrived recently."

KIKI nodded. "Something must have happened here, causing this shelter to fall and allowing the abnormal entities to invade the underground passages."

Fire Bro crossed his arms. "So we came all this way for nothing?"

Lin Xian's gaze sharpened. "At least we've figured out how that group arrived and planned to escape."

"You mean... the submarine?" KIKI asked.

Lin Xian monitored the warehouse sinkhole through his surveillance drones, ensuring the black worm monster hadn't emerged. "But we still haven't found that middle-aged man who used the Forbidden Artifact. Also, submarines travel through deep waters, which should theoretically be more dangerous than the surface. That part doesn't add up..."

KIKI looked worried. "I wonder how Sister Chen is doing. If the Dark Mark hasn't been removed, those abnormal entities drawn by the Sanctum might devour our Infinite train alive."

Lin Xian's expression darkened. His communication drones couldn't reach Chen Sixuan across the sea, making him uneasy. His original plan had been to strike directly at the Sanctum's headquarters to prevent another attack on the Infinite after nightfall. With giant creatures surrounding the city, even a simple Bait Agent could push them into dire straits. That's why he'd sent Chen Sixuan's team to relocate and remove the mark while he pursued the escaping Forbidden Artifact user.

But before they could enter the underground headquarters, they'd been blocked by an invisible abnormal entity emitting terrifyingly concentrated dark energy in the passageway. Though large, it wasn't on par with special-level or even A-rank entities. Yet Lin Xian sensed its threat level might approach S-level darkness contamination—otherwise, A Bai wouldn't have been so severely affected.

"That thing's blocking the passage, so we definitely can't get through," Ning Jing said. "But... could the people below already be dead?"

"Dead would be good news," KIKI remarked. "We're just worried they'll attack us again after nightfall. Once we survive tonight, we're leaving this hellhole. We're not interested in this base anyway."

Lin Xian fell deep in thought, flashes of Gu Zheng's memories causing a sharp pain in his head. Suddenly, he heard a dull, drum-like sound and snapped his eyes open. "Now I know what that noise was—it's coming from inside the submarine!"

"Captain Lin?" Ning Jing looked at him.

"The Sanctum has a submarine unit besides their surface team," Lin Xian said grimly. "Strange. The Falcon Sea Group avoids dangerous waters, yet they dare travel through the deep sea..."

KIKI turned to him. "You suspect they have a way to avoid the abnormal entities?"

Lin Xian shook his head, his expression grave. "If the Sanctum Organization truly communicates with the dark civilization—if they're the dark civilization's human opposition group—then it makes sense they'd have such methods."

"True enough," KIKI said. "If they're traitors to humanity, the dark civilization might have given them some kind of... pass."

"A pass?"

"You know what I mean. If the dark civilization considers them allies, maybe they really can avoid attacks from abnormal entities?"

Lin Xian frowned. "But this afternoon, that group clearly came under attack."

"This discussion is pointless," Fire Bro interrupted. "We're already here. We need to investigate this submarine base. Taking initiative beats waiting for the Sanctum's lackeys to strike first. Besides, a military base like this might have useful equipment."

"Like nuclear submarines?" Xiao Qing chimed in quietly.

Ning Jing added, "Or perhaps some Forbidden Artifacts or disaster plants."

"But... how do we get in?" Lin Xian asked.

"There are ways," KIKI said, rapidly operating her mobile terminal. Soon, she'd mapped the base's general layout. "This submarine port has an inner harbor, indicating top-secret clearance. That means the port was built inside the island's mountain. Look—this island's terrain is special, with a massive underground cavity and a deepwater cliff. It's the perfect hidden inner harbor. No wonder they built here. Submarines could resupply and undergo maintenance completely undetected by satellites."

She pointed to a valley on the offline map. "There's a secret passage here—it looks like a sealed mining tunnel, but it's actually the main entrance. The flood channel beneath the prison is the backup entrance, located below Prison Building 1. The hole under that warehouse was probably accidentally blasted open. Other than these two routes, the only remaining access is through the submarine's deepwater floating harbor channel."

"Forget the deepwater harbor. We'll have to try the land routes," Lin Xian decided.

"With that monster blocking one passage, does that mean we can only attempt the mountain entrance?" Ning Jing asked.

As Lin Xian and KIKI analyzed the blueprints, they realized the entrance structure was highly secure. However, this secret submarine port appeared quite old. After the Federation government's establishment, regional powers' secret military forces had centralized under the Dragon Kingdom's leadership, leading to the birth of the Starfleet.

"That tsunami flood channel is part of the submarine base, designed for tide diversion and emergencies. If abnormal entities have infiltrated it, the base interior can't be safe either," Lin Xian said, frowning. He usually avoided nighttime operations—even a level-one Dark Mark spelled extreme danger. But with the island surrounded and the Oceanic Titan likely lurking nearby, how could they just wait for death when clearly targeted by the Sanctum?

Moreover, Laine from the Falcon Sea Group had mentioned a Forbidden Artifact that might affect the Garland underwater volcano. Now it seemed likely connected to that escaped middle-aged man. Lin Xian felt compelled to investigate this threat.

"Hold on. Night operations are always tricky, and this island, though small, is no safe haven. The real headache is Viola's absence, but I'll send a scout robot first to scan the spirit values along the path for safety."

KIKI nodded. "Good idea."

Lin Xian summoned the Black Star Forge, producing an ACT mech identical to Qian Suxun's. He'd designed this mech to test neural interface systems for ultra-large mechs, even adding remote-control improvements to handle tasks beyond drones' capabilities. With no better option, he deployed it to replace Viola for long-range reconnaissance.

He assigned operation duties to KIKI, who immediately took charge, plotting waypoints. Soon, from the prison watchtower under cover of darkness, a nimble humanoid mech accompanied by several scout drones descended and swiftly vanished into the woods. The sudden movement startled zombies that had escaped the prison, triggering howls that echoed through the night.

Meanwhile, Lin Xian redirected drones toward the main island to rebuild communication links. Though rough seas might destroy low-flying drones, he couldn't afford to worry—drones were replaceable, and abnormal entities couldn't trace him through them. His priority was contacting the Infinite to ensure their base's safety.

The prison watchtower stood silent, the team communicating through power armor displays, only faint energy lines glowing on their armor exteriors. The surrounding darkness felt oppressive—even C or D-rank abnormal entities became troublesome at night.

In KIKI's control interface, she'd fully synced with the ACT mech, guiding it swiftly along a mountain road to the island's northwest foothills. Night vision revealed what appeared to be an abandoned military outpost. The mech bypassed barriers, arriving at a massive blast door resembling a bomb shelter entrance.

"This hasn't been used in ages..." KIKI muttered as the mech accessed a rusted terminal panel beside a smaller door. Emergency circuits groaned to life. "It's opening," KIKI announced over comms, her voice tense with excitement.

The ACT mech stood before the colossal blast door as rusty hinges shrieked, revealing a dark passage.

"Lots of junk inside—untouched for decades. The outer door shows forced entry marks, probably survivors who couldn't breach this blast door..."

From the prison tower's shadows, Lin Xian watched the mech's feed through his armor display. Night vision rendered everything in ghostly gray-green, as if the world wore a deathly filter.

"Air composition: low oxygen, high humidity, trace hydrogen sulfide," KIKI reported. "This place has been sealed too long—possible water accumulation or corrosive gases inside."

Lin Xian studied the synchronized footage. "Strange. Was I wrong? No signs of recent passage here. Did they really use the flood channel?"

The ACT mech stepped inside, its metal feet whispering through dust. Emergency lights along the tunnel had long failed, leaving only the mech's searchlight to pierce the darkness. Dust motes swirled like specters in its beam.

"Garage area," KIKI murmured.

The mech's view revealed rows of military trucks and armored vehicles, their tires deflated, bodies thick with dust. Some doors hung ajar, as if occupants had fled in haste, never to return.

"These vehicles haven't moved in decades," KIKI said, voice tight. "Even the paint has oxidized and peeled."

Lin Xian remained silent, watching as the mech's camera swept over a military jeep. A faded uniform hung in the driver's seat, its sleeve bearing a barely visible serial number.

"Storage warehouse." The mech proceeded through another blast door.

The space brimmed with crates and metal shelves, but most supplies had rotted—dried, moldy food packages, rusted cans with illegible labels. In one corner...

"There's a hangar here." KIKI switched views.

The hangar stood more spacious yet equally dead. Several hypersonic fighters rested on their pads, wing paint peeled away to expose rusted skeletons. Beyond lay an armory stocked with rifles, pistols, and ammunition crates. Only weapons in special containment appeared functional—most had corroded beyond use, bullets oxidized and misshapen in their magazines.

"Seems like... just an ordinary military base sealed for decades. Anything here would be unusable now."

"Wouldn't survivors hiding near the prison have searched this place? Without military guards, they should've found a way in," Ning Jing wondered.

As KIKI's mech and drones scanned the environment, Lin Xian suddenly spoke: "Stop."

"What is it?"

"Two o'clock. Raise the angle."

At his direction, KIKI adjusted the view upward, revealing a faded but unmistakable symbol on a massive tunnel wall—the radiation trefoil!

At the base's deepest point, a giant lead door appeared in night vision. Simultaneously, the ACT mech's Geiger counter spiked to lethally high levels.

"Now we know why..."

Pitch darkness enveloped the island as Lin Xian's team—KIKI, Shiori, and Ning Jing's squad—entered the abandoned base. Watching the Geiger counter, Lin Xian said gravely, "Coming here without full-coverage power armor would be suicide. But this radiation level doesn't suggest a large-scale leak."

"Strange. Could they still have nuclear fuel here?" the group wondered aloud as they reached the sealed door.

Lin Xian examined the mechanical door and activated his Mechanical Heart. With clanking mechanisms, the long-sealed door slowly opened. The team fell into defensive positions as a gust of stale air rushed out, revealing a startling contrast beyond.

Past the door lay a steel-and-mesh enclosed area with rail tracks. Lin Xian absorbed a small section, finding the ground spotless and lights still functioning—clear signs of recent activity.

"Careful. This might be their hideout."

Lin Xian signaled readiness before sending drones ahead. But upon exiting the passage, the sight before them stunned everyone.

A colossal four-armed mechanical structure towered over a 300-meter-wide pit, with four ventilation shafts descending majestically.

"What... is that thing?" KIKI gasped.

Lin Xian shook his head, leading them down stairways. At the lower level, an even more astonishing sight awaited—the massive mechanical column plunged hundreds of meters into a red molten pool segmented into precise zones. An enormous retractable cover loomed above. Immediately, their armor's temperature sensors spiked as searing heat waves washed over them.

"Looks like some geothermal device, but... why such high radiation?" KIKI asked.

Lin Xian shook his head. This surpassed all expectations—no nuclear leak, yet this gargantuan apparatus was clearly more than just a "hideout."

"This thing... doesn't look like any military facility..."