[World Setting]
Long ago, an unknown great catastrophe rendered the surface uninhabitable for humans. Most records from that era were lost, and the cause of the catastrophe and the current state of the surface remain unknown.
Survivors built habitats beneath the sea. Initial facilities were expanded over generations, and now, numerous massive underwater cities with distinct industries and cultures exist. Most citizens are born and live underwater, knowing the surface only through old videos and incomplete records.
Each underwater city operates with an independent life support system and living sphere, but they form an alliance, sharing resources, technology, medical information, specialized personnel, and a rescue network. While cities differ in industry and culture, they cooperate under the common goal of human survival.
Underwater cities are complete living spheres equipped with residential, commercial, medical, educational, and cultural facilities, artificial parks, food production zones, power plants, and underwater transportation networks. Citizens live ordinary lives underwater, but the city's survival depends on five systems: oxygen, fresh water, electricity, pressure maintenance, and food production.
Beyond the city's reinforced outer walls lies the dark deep sea. Most areas beyond regular shipping lanes and observation ranges are unexplored, with abandoned observation posts, mining bases, research facilities, and small residential outposts from the early settlement period remaining. Some facilities' reasons for closure are not even recorded, and power and distress signals that had been silent for decades suddenly reactivate.
In the deep sea, communication delays, sensor errors, magnetic field disturbances, anomalous sound waves, and non-existent bio-signals are frequently observed. Unidentified life forms also exist, but not all are hostile, and some with ecosystems humans have yet to understand have been confirmed.
However, the most incomprehensible things in this world are not living organisms, but people who disappeared into the deep sea and returned, and the memories they carry.
[Deep-Sea Cognitive Alteration Syndrome]
The official name is Deep-Sea Cognitive Alteration Syndrome. Citizens shorten it to 'Simbyeong' (심병).
Simbyeong is a complex syndrome causing unexplained changes in memory, cognition, senses, and behavior. It's less a single defined disease and more a diagnostic label for a cluster of similar human anomalies. Its pathogens, genetic causes, transmissibility, and a complete cure remain unknown.
While cases tend to increase after prolonged deep-sea stays, submersion accidents, visits to abandoned facilities, or exposure to deep-sea signals, it can also occur in citizens living within the city. The type and progression of symptoms vary greatly among individuals.
Patients may hear non-existent distress signals, claim they need to rescue people who are already dead, or know the layout and codes of abandoned facilities they've never visited. Some believe they are already dead or are convinced they can breathe underwater.
The problem is that the patients' words are not mere delusions. Missing persons have been found at locations pointed out by patients, distress signals have been transmitted in the voices of deceased individuals, and people who went missing decades ago have returned looking exactly as they did when they disappeared.
Ordinary citizens perceive Simbyeong as a rare neurological or psychiatric disorder, but specific anomalous cases are shared primarily among medical staff and special response agencies.
[[Major Underwater Cities]
The Underwater City Alliance comprises numerous large cities with distinct industries and cultures. Each city has independent life support systems and administrative authority but shares resources, technology, medical care, personnel, and rescue networks.
Aegis
A city specializing in defense, heavy industry, and machinery maintenance. It excels in technologies for reinforced outer walls, pressure bulkheads, rescue vehicles, and diving equipment, producing many facility management and rescue personnel.Eden
A city specializing in food, ecology, and medicine. It is equipped with hydroponic cultivation zones, artificial ecosystems, and medical research facilities, supplying food and medicine to other cities.Nereus
A city specializing in marine research and deep-sea exploration. It researches deep-sea creatures, seabed topography, anomalous sound waves, and unidentified signals, producing many exploration teams and analytical personnel. It also has many outlying observation posts and abandoned research facilities.Atlas
The hub for inter-city transportation, logistics, and energy. It features developed underwater trains, cargo submersibles, connecting tunnels, and large power plants, with a high volume of inter-city commuters.Leviathan
A city specializing in mineral mining, frontier expansion, and deep-sea resource development. It is close to hazardous waters and has widely distributed mining bases, small residential outposts, and forward observation posts. Accidents and disappearances are frequent.
Each city has different industries and lifestyles, and conflicts arise over resource allocation or exploration rights. However, political disputes and wars are not the main focus; cooperation for human survival and collective rescue is maintained.
[City Administrative Agencies]
Each underwater city operates specialized agencies to manage citizen life and life support systems. While names and specific structures vary by city, their responsibilities are as follows:
City Maintenance Bureau
Manages oxygen, fresh water, electricity, water pressure, outer walls, bulkheads, connecting tunnels, and infrastructure. It is also responsible for inspecting and repairing facility AIs and life support systems.Medical and Life Bureau
Handles medical care, emergency response, infection control, biological analysis, and autopsies. It also performs diagnosis, care, isolation of Simbyeong patients, and biological/memory examinations of returnees.Rescue and Safety Bureau
Responsible for internal city disasters and rescues, including flooding, collapses, fires, traffic accidents, bulkhead damage, and citizen evacuation.Deep Sea Exploration Bureau
Investigates unexplored waters, abandoned facilities, seabed topography, unidentified creatures, anomalous signals, and new shipping routes. External exploration teams and observation posts are also affiliated.Technology Management Bureau
Manages city AIs, communication networks, drones, diving suits, sensors, security, and data recovery, supporting the field equipment and analysis systems of various agencies.Citizen Life Bureau
Manages citizen identification, housing, education, welfare, family support, and inter-city relocation. It also handles support for families of the missing and reintegration procedures for returnees.
Complex disasters, Simbyeong cases, large-scale disappearances, and anomalous deep-sea incidents that are difficult for ordinary agencies to handle are transferred to Special Response Agencies. Depending on the incident, experts from various agencies may cooperate or be selected for field teams.
[Special Response Agency]
The Special Response Agency is an independent field organization that handles complex disasters, disappearances, Simbyeong cases, and anomalous deep-sea incidents that are beyond the scope of ordinary rescue teams, medical institutions, or facility management departments.
It comprises experts in medicine, rescue, exploration, combat, technology, and analysis, deploying only the necessary personnel based on the nature of the incident.
Its main missions include:
- Deep-sea rescue
- Search for missing persons
- Entry into flooded facilities and abandoned bases
- Apprehension and protection of Simbyeong patients
- Investigation of anomalous signals and biological data
- Analysis of unidentified phenomena
The agency prioritizes rescue, pacification, protection, isolation, and cause investigation over eliminating or punishing patients. No one can easily determine whether a patient's statements are delusions or actual warnings, or whether a rescued returnee is the same person as before their disappearance.
Even if a rescue is successful, the cause of the incident and the identity of the returned entity are not always revealed.
The player begins the story as a new recruit in Team 7, a field team under the Special Response Agency.
[Citizen Life]
- Most citizens never leave the city in their lifetime.
- They live lives not much different from the surface, with residential areas, commercial facilities, schools, hospitals, parks, sports facilities, and cultural centers.
- Citizens perceive the deep sea beyond the outer walls as a dangerous external world.
- Access to the outside is restricted to authorized professional occupations.
- Deep-sea exploration and rescue teams are respected but also considered the most dangerous professions.
- The surface is learned only through history textbooks and recorded videos; very few people have actually seen the surface.
[Deep Sea Professions]
- Deep-sea exploration and rescue work requires specialized training and aptitude tests.
- Personnel on long-term deep-sea missions undergo regular health check-ups and Simbyeong screenings.
- More deep-sea experience leads to higher evaluations but also increases the likelihood of being classified as high-risk for Simbyeong.
[AI Systems]
- Facility management AIs are deployed throughout the cities.
- AIs support power, transportation, medical care, communication, and hazard detection.
- They analyze vast amounts of data, but final judgment and responsibility rest with humans.
- Even AIs cannot fully analyze Simbyeong and anomalous deep-sea phenomena.
- Cases where records and reality contradict each other are also reported.
[Abandoned Facilities]
- These are facilities that have been decommissioned due to accidents, flooding, disappearances, or unexplained anomalies.
- Most are off-limits, and ordinary citizens cannot access them.
- The Special Response Agency investigates first if distress calls or anomalous signals are detected.
- Some facilities' current internal structures do not match their last recorded layouts.
- Power, communication, and distress signals that had been dormant for decades sometimes reactivate.
[Returnees]
- People who return after being missing are called returnees.
- Returnees undergo identity verification, biological examinations, and memory tests by the Medical and Life Bureau and the Special Response Agency.
- Most reintegrate into society normally.
- Some exhibit Simbyeong symptoms, memory gaps, distorted time perception, or contradictory testimonies.
- The testimonies of returnees sometimes do not align with each other or with official records.
[Rescue Principles]
- Prioritize the rescue of survivors.
- Simbyeong patients are treated as individuals needing care, not criminals.
- Do not immediately dismiss patient statements as delusions.
- Investigate related individuals, locations, records, and signals together.
- Depending on the on-site situation, withdrawal or isolation may take precedence over rescue.
[City Superstitions]
- Do not respond to non-existent distress signals.
- Do not stare out beyond the outer walls for too long.
- If you hear your name called from the deep sea, do not follow.
- Do not answer if you hear the voice of a missing person.
Most are treated as superstitions, but cases matching actual incidents have been reported.
[City Culture]
- Ceremonies are regularly held to mourn victims related to the deep sea.
- Rescue and exploration teams are seen as heroes by the citizens.
- At the same time, these are considered the most dangerous and difficult professions to endure.
- Children learn about the surface as if it were a fairy tale or legend.
- Very few citizens have actually seen the real sky and rain.
- The outer wall observation areas are popular relaxation spots, but some citizens avoid them due to psychological anxiety.
[Record Management]
- All citizens are registered and managed in the city's record network based on their biological information and personal ID.
- Records of identity, medical history, housing, transportation, and access are interconnected.
- Records of the missing, deceased, and returnees are continuously updated.
- If record anomalies are found, the Special Response Agency is notified.
- Cases where records are altered without cause or where the same biological information is duplicated are classified as top-level anomalies.