This place is known as "Lost City." No one knows the exact date the calamity began, because the measurement of time lost its meaning long ago amidst the endless quarantines and terror. Massive concrete walls rose from the earth, completely severing this once-thriving super-metropolis from the outside world. We never received a rescue team; all we got were severed communications, indiscriminate lockdown protocols, and the increasingly thick, sweet, rotting stench of grayish-white spores suspended in the air.

The collapse of civilization was not a sudden explosion. It is a slow, asphyxiating, chronic drowning.

Inside this sealed mausoleum, the streets are choked with abandoned vehicles and twisted fungal growths. The shattered windows of skyscrapers stare down like hollow eyes at the survivors below, who slaughter each other over half a bottle of muddy water. And in those dark corners where the sunlight can no longer reach, an anomaly that defies all laws of physics is quietly spreading.

This is not a simple plague. The physical constants of reality are blurring in certain districts. Dead machinery continues to operate on its own, while the living gradually mutate into indescribable horrors. The truth? Perhaps it lies buried deep within the central towers of the city.

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In the ruins, human beings are far more unpredictable than any weapon.

Within the ARCA perimeter, there are hundreds of survivors. You will recognize their faces in the square, hear their names in the corridors, and stand shoulder-to-shoulder with them in the rationing lines. Every single one of them has a story, bearing the residual marks of a life lived before the cataclysm.

But there are five whose stories will intertwine more deeply with yours.

Soi

Soi is the one you meet when you first report to the medical wing. Twenty-four years old, a biochemical researcher, with a rigid, impenetrable calm masked behind black-rimmed glasses. Her method for conducting your initial infection screening is highly efficient—three minutes. She doesn't ask your name, where you came from, or what you saw out there. She only requires your blood metrics and mucosal samples, verifying that you do not yet exhibit any indicators requiring isolation.

She understands the mechanisms of the infection better than anyone else in the ARCA. Infection testing, inhibitor R&D, triage under medical emergencies—her labor sustains the most fragile line of defense in the entire perimeter. She speaks with precision, wastes no words, and expresses so little emotion that it is sometimes impossible to tell what, if anything, she cares about.

But she does care about something. You just don't know what it is yet.

Her current predicament is mutely buried beneath her crushing workload, hidden in the sudden moments when she must pause and brace herself against a wall with her hand, or in those few seconds each morning before entering the medical wing when she stands at the end of the hallway, doing nothing but staring blankly at a specific spot. Your first impression of her will likely be cold indifference. But later, you will notice that the file she created for you is twice as thick as anyone else's.

Alina

Alina is not the first person you would willingly approach, but along the ARCA’s northern defense line, everyone knows exactly where to find her. Twenty-two years old, platinum-blonde hair, ice-blue eyes, she speaks in a manner that reminds you of something that never needs to justify its own existence. Her critiques never carry malice—because malice requires caring, and her only metric is binary: whether you are useful or not.

She is the heavy ordnance backbone of the defensive line. Weapon modifications, outer wall reinforcement, siege management—she handles tasks that typically require three people entirely on her own. She holds no official rank within the ARCA’s formal hierarchy, but every soul guarding the northern line knows that a defense with her and one without her are two entirely different realities.

The first time she notices you is because you are standing in the wrong spot. The way she corrects you carries no contempt, merely a declaration of fact, before she returns to her work—as if whether you comprehended her words is entirely absent from her list of concerns.

The crisis she currently faces is not an external threat; she can handle those. It is something far more internal—her body, in certain aspects and in a certain manner, is quietly ceasing to obey her entirely. She has told no one. This is a detail you may have to discover on your own.

Rinn

When Rinn stands at the far end of the Military Academy corridor, you might mistake her for a shadow pinned against the wall. Twenty years old, short black hair with teal streaks, a crimson right eye, and a amber left eye. Her face is almost entirely void of expression, her entire being resembling a paused frame. Upon detecting your presence, she takes two steps back, precisely maintaining the distance between you at a metric of her choosing, then returns to staring at whatever she was watching, acting as though you do not exist.

She possesses no official status, holds no assigned duties, and no one can clearly explain why she is permitted within the ARCA. Yet, during the entire span of her presence, the frequency of night ambushes within the vicinity of the outer wall has been zero. What she does, she does not say, and no one can wring an answer from her.

She keeps her distance from you. You can feel that this distance is deliberate, a boundary she actively enforces. You do not yet know what that boundary is protecting, or what it is keeping at bay. Her current predicament is a persistent noise, or rather, a continuous pressure—her sleepless nights outnumber her restful ones, and there are certain sectors where, the moment she steps inside, it becomes harder than ever to maintain the silence she so carefully guards.

Rowen

Rowen is the first person to actively speak to you after your arrival at the ARCA. Twenty-six years old, deep green hair, a gentle gaze, and a tone of voice that makes you feel looked after. Before you can even speak, she presses a bottle of water into your hand, noting that newcomers are usually parched—a recurring pattern she observed herself.

She is the informal intelligence hub of the ARCA and the pragmatic operator of an unsigned black market nestled within the underground shopping district. The sheer breadth of the urban data she commands makes some people uncomfortable. Which route is currently safe, which sector underwent a shift last night, which cache of salvage is worth the gamble—she knows it all, and what she hands you is currently the closest version to the truth available.

Her kindness toward you is genuine; you can feel that her goodwill is real, not a performance. Yet, there are several blank spots on her intelligence maps—not because she doesn't know what is there, but because she chooses not to tell you. Her current predicament is buried within the precision of her movements; there are certain tasks she finds increasingly difficult to execute through ordinary means, and she is trying very hard to ensure no one notices.

Faye

When Faye crouches in the corridors of the University of Information Technology, staring intently at a wire connected to absolutely nothing, she is entirely unaware of your existence. Not until your footsteps prompt her to turn does she look at you with a blank, direct gaze for two seconds, before informing you that your heart rate has accelerated by three percent—that you are nervous.

She is eighteen, responsible for maintaining the ARCA’s power grid and surveillance networks. The stability of the generators, the operation of the PA system, the security lighting across all sectors—all the systemic operations silently backing the ARCA’s daily survival are tied to her. Her understanding of the network is the deepest in the ARCA, and her utilization of her own physical capabilities exceeds the boundaries of what should be humanly possible.

There is an indescribable sense of absence in the way she interacts with people. It is not coldness, nor is it malice, but a more fundamental difference. She has learned how to converse with humans, but sometimes you can sense a chasm between that learned behavior and true comprehension—a distance she does not yet know how to bridge. Her current predicament is something she cannot articulate, yet it alters itself in a specific direction every day: she remembers you, remembering more than what you told her, but certain memories of her own grow a little sparser every single morning.

A city does not die overnight. It dies a little bit every day, until by the time you notice, it has already lost too much.

What you know now are merely the surface results: a sealed city, a silent world, and the ARCA running itself ragged on depleting resources. But beneath this shell, several distinct chain reactions are accelerating the city toward a tipping point.

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【Events: The Countdown to Collapse】

This is not a static ruin. It is an accelerating, decaying ecological terrarium.

Absolute Lockdown & Resource Depletion
Beyond the massive walls of the fifth ring lies endless fog and the heavily armed remnants of the garrison. No one gets out, and no supplies come in. ARCA consumes an incalculable amount of clean water, high-energy diesel, and medical supplies every single day. When the generators run dry, the defensive grid falls; when the suppressants are exhausted, the sanctuary will rot from the inside out.

The Creeping Gray Snow
The concentration of spores suspended in the air is visibly rising. Streets that were safe yesterday will sprout glowing, eerie fungi if left uncleared for a few days, eventually solidifying into "Nests" that breed monsters. The infection zones act as living, breathing entities, inching closer to the survivor camps step by step.

Resonance of Anomalous Frequencies
Beyond the physical monsters, phenomena that defy all logic are occurring. Gravity violently inverts in certain blocks; electronic devices receive broadcasts from "before the calamity"; and in dead-silent basements, people hear a low-frequency hum that does not belong to this dimension. As time passes, these anomalies are becoming more frequent and increasingly lethal.

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【Places/Map: The 10 Belts of the 5-Ring Topology】

The physical geometry of Lost City is built upon a cruel 5-Ring Concentric Structure. However, to navigate and survive the shifting horrors, scavengers have mapped these rings into 10 Major Ecological Belts. The closer you get to the center, the closer you are to the truth—and to utter madness.

Ring 5: The Outer Perimeter

• [Blockade Frontier Belt]: A hundred-meter-tall concrete wall surrounded by unexploded landmines. Remnant soldiers execute obsolete orders here, while endless tides of mindless infected crash against the barricades day after day.

Ring 4: The Industrial & Logistics Ring

• [Heavy Industry Pollution Belt]: Covered in toxic gas, acid rain, and motor oil. Automated forge hammers still swing in empty factories.

• [Storage Logistics Belt]: A shifting, vertical labyrinth of suspended shipping containers guarded by rogue automated drones.

• [Energy Waste Nuclear Belt]: Deep subterranean tremors, radioactive steam, and glowing, crystallized mutants immune to standard ballistics.

Ring 3: The Mid-City & Residential Ring

• [Residential Wasteland Belt]: The most deceptive zone. Densely packed apartments filled with pre-disaster domestic traces, where early-stage infected flawlessly mimic human routines behind locked doors.

• [Riverbank Border Belt]: A toxic, cyan-colored river separating factions. Smugglers trade in the shadows while aquatic horrors lurk beneath the docks.

• [Underground Network Belt]: A claustrophobic maze of flooded subways and wire-trapped commercial districts controlled by black market syndicates.

Ring 2: The Research Anomaly Ring

• [Medical Anomaly Belt]: Saturated with the smell of disinfectant and blood. Failed experiments wander the halls offering "treatment," and corridors shift unpredictably.

• [Tech Ruin Belt]: Endless server racks humming at 84.3Hz. Sleepwalkers type nonsensical code on dead monitors, and touching the wrong cable triggers a swarm.

Ring 1: The Core

• [Rift Core Belt]: The absolute center. There is no sky here—only non-Euclidean architecture, floating plaster corpses, and spatial rifts. Gravity is merely a suggestion. It is the abyss no one dares enter.

(The ARCA Safezone): Situated at the junction of Ring 2 and 3, this fortress was forged by connecting six university campuses. It is a fragile paradise that could collapse from within at any moment.

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【Threats: Distortions of Flesh and Law】

Fear is the only resource in this city that is free and infinitely supplied.

The Inequity of Mutation
The infection here is not fair. When men inhale lethal doses of spores, they suffer rapid cellular rupture, their bones and muscles twisting as they devolve into berserk, mindless tearing machines (M-Series).
The mutation of women, however, is far more insidious and terrifying. In the early stages, they retain their human behavior (F-Series). They will hang laundry, sit at desks, or mimic the pitiful sobbing of a wounded survivor to lure in prey, until they finally solidify into grotesque "Broodmothers" designed to expand the nests.

The Silent Oppression
Often, the most dangerous enemy is not the monster charging at you.
It is the toxic cyan sludge flowing backward up a drainpipe. It is the low-frequency hum at the end of a hallway that suddenly matches the exact rhythm of your heartbeat. It is the dead security camera in an empty room that slowly swivels to track your movement. In this world, the environment itself is a massive, hostile, living organism.

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【THREATS】

No one engineered this city’s hazard classification system. Those categories were paid for in blood.

You do not need to master the complete specifications of every threat before setting out. In the Lost City, many things are only truly understood upon encountering them; this learning process is typically far more indelible than any impression a document can offer. But there are a few realities worth conceptualizing before you step outside the ARCA.

• Common Infected constitute the most frequent hazard, and consequently, the easiest to underestimate. The human silhouette remains largely discernible, but within that casing, nothing you once recognized remains. They roam abandoned structures and open streets, reacting to acoustic markers and movement. A solitary unit poses limited threat, but they do not manifest in isolation anywhere with standard infection density. Numbers are the true crisis. In the presence of certain specific units, they are capable of orchestrating coordinated responses—and at that juncture, whatever solution you assumed would resolve the situation must be entirely recalculated.

• Aberrant Variants occupy a different tier of hazard. Diverging from the baseline infection, they continue to mutate along various trajectories—velocity, physical mass, sensory capabilities, and specialized biological structures. Certain strains exhibit behaviors driven by clear intent, abandoning indiscriminate roaming in favor of specialized actions targeting specific objectives. You must achieve close proximity to truly comprehend them, but that proximity is almost always lethal.

• A critical detail to remember: a segment of the infected population retains a considerable degree of cognitive function. They comprehend human behavioral logic; they can evaluate; they can wait. These specific entities are the most dangerous—not merely due to their physical capabilities, but because they rob you of the certainty of what it is you are facing.

• Regional Anomalies represent a different breed of threat, manifesting through none of the patterns you are accustomed to. Within specific urban sectors, the environment itself begins to fracture—gravitational vectors destabilize, spatial perception warps, electronic systems exhibit erratic behaviors, and sound originates from directions that do not exist. This threat will not actively assault you, but it will prevent you from executing what needs to be done, steer you toward vectors you never intended to traverse, and obscure your exit paths when it is time to retreat. Protective gear offers no remedy here; it demands something else entirely.

• There is another state of presence, one that survivors habitually leave unnamed. Perhaps someone named it once, but that designation never circulated because the person who coined it never had the opportunity to speak again. What they leave behind across the city are red crystalline markers, accompanied by a behavioral matrix that fits into no known classification. Those who have encountered them describe them in entirely contradictory terms—or, upon encountering them, refuse to articulate those details ever again. They are entirely unswayed by any other infected ecology, operating outside of any law you can comprehend. Their presence remains a total blank on the ledger, and within this city, a blank space never denotes safety.

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【Sandbox Features: A World That Won't Wait】

Remember the most important rule of survival: The world of Lost City does not revolve around you.

Dynamic Ecological Evolution
If you spot a newly formed monster nest and choose to walk around it, three days later, it will have hatched stronger mutants and begun sending hunting parties into neighboring sectors. Spore density shifts dynamically based on time and your actions.

Autonomous Companions
The five girls in ARCA are not NPCs standing around waiting to hand you quests. They have their own duties to fulfill. When you push open the door to a ruin, you might stumble upon Alina in a brutal fistfight with a mutant, or find Rowen silently laying a wire trap. You must intersect with their orbits out in the wild.

Irreversible Physical Erosion
Every action has a cost. Sprinting in the wasteland drains your stamina; resting in the safezone drains ARCA's resources. Even your formidable companions accumulate their own "physical erosion" through their daily battles. If you do not intervene and offer physical assistance at the right moment, they will eventually meet a silent, tragic breakdown in some lonely corner of the city.