── CHAPTER 1. Prelude to Disaster: The Great Outbreak in Korea (PROLOGUE)

In August 2026, South Korea's civilization was permanently paralyzed in just 72 hours. The root of all evil was the greed of a giant US private corporation seeking a monopoly on capital and its Korean branch, where their advanced bio-hub was located. Conducting illegal biological experiments based on secret funds smuggled from various countries, they plotted to leak a virus while disguised as victims to skyrocket the value of their own vaccine.

However, the virus mocked human calculations, undergoing explosive genetic rearrangement mutations. The Seoul metropolitan area, boasting one of the world's highest population densities, was the perfect incubator for the virus. All-round indiscriminate transmission occurred through subway commutes and dense public transport infrastructure, and the government's emergency martial law and urban isolation defense lines collapsed like dominoes. The Korean Peninsula, where administrative functions have vanished, is now an isolated hell filled with moving corpses.

── CHAPTER 2. Basic Physiology Rules of the Infected (THE DEAD)

To survive in the Korean terrain where firearms are regulated, one must perfectly understand the biological limits and weaknesses of the infected.

Brain Destruction as the Sole Neutralization: The infected are in a state where all organ functions from their previous life have stopped. Since only the mutant virus that has seized the brain cells forcibly drives the body, they will not stop attacking even if their limbs are severed unless the brain tissue is physically and completely destroyed.

Biological Limits of Cell Necrosis: Although it seems they can engage in long-term activity without separate nutritional intake because the virus constantly supplies energy, the host's cell decay accelerates if there is no organic matter influx at all. Because of this, they have a weakness where their mobility dramatically decreases in extreme winter climates or perfectly isolated, sealed areas.

Acoustic Tropism and Micro-vibration Detection: Their vision and heat-sensing abilities are paralyzed, but their ability to capture subtle sounds and physical vibrations has evolved to a terrifying degree. Since they react immediately to small frictional noises in alleys or inside apartments, survivors must attach thick cloth to the soles of their shoes to minimize vibration propagation during night activities.

Variability of Movement Speed: Depending on the host's physical condition before death and the virus's activity level, they appear randomly with speeds ranging from a normal walking pace to a near-sprint jogging speed, so carelessness leads to immediate death.

── CHAPTER 3. Infection Mechanism and Close-quarters Environment (ENVIRONMENT)

Korea's environment, where civilian firearm possession is impossible, forces survivors into extreme struggles.

Strong Fluid Permeability: There is no airborne infection, but transmission is immediate the moment the infected's contaminated blood or saliva touches a wound or mucous membrane. Even a trace amount of body fluid seeping through gaps in clothing or old protective gear during combat is a target for absolute blocking.

Fatality of Residual Substances on Teeth: Concentrated viral substances that do not die even at room temperature remain on the surface of the infected's teeth. Even a light abrasion or skin scratch immediately collapses the body's immune system.

Forced Close Combat and Fortification: Survivors without firearms must rely on cold weapons such as baseball bats, archery bows, and private blades. Accordingly, they have established a survival method of extremely controlling noise, such as fortifying high-rise apartment complexes with sturdy concrete exterior walls, welding fire doors shut, and moving only via ropes on the outer walls of balconies.

CHAPTER 4. The 0.01% Disaster: Special Variants (VARIANTS)

These are high-risk evolved entities that manifested with only a 0.01% probability, combining Korea's high-density environment and genetic traits. They release specific pheromones that accelerate the mutation of surrounding infected, so failure to kill them early leads directly to annihilation.

1. Brute (Strength-Enhanced Type) Features: A giant entity with abnormally fused and enlarged muscle tissue.

Danger: Its skeletal density is comparable to concrete, so normal cold weapon strikes do not work. With superhuman strength transcending human limits, it breaks through steel fire doors of apartments or vehicle barricades with its bare body to clear a path for the herd.

2. Scout (Hearing-Sensitive Type) Features: An entity with abnormally amplified auditory organs and cranial structure.

Danger: It captures even the slightest sound of breathing within a complex or the vibration of stairs. Upon discovering a target, it emits a high-frequency scream to forcibly gather surrounding zombies, and this scream causes extreme noise interference in survivors' analog radio systems, paralyzing communication networks.

3. Leader (Army-Commanding Type) Features: A leader entity possessing a low level of tactical computational intelligence.

Danger: It perfectly utilizes the complex large-scale apartment complexes or maze-like Korean alleyway terrain. It employs organic military-style tactics, such as instructing subordinate infected to ambush or pre-emptively blocking survivors' escape routes.

4. Runner (Speed-Enhanced Type) Features: An entity with a lightweight skeletal structure and explosively evolved lower body muscle fibers.

Danger: It sprints at speeds approaching vehicle driving speeds and freely scales walls. In particular, it is capable of vertical breakthroughs to upper floors by climbing gas pipes on the exterior walls of apartments, ambushing survivors in high-rise safe zones from the rear.

5. Guardian (Hard-Armor Type) Features: An entity whose outer skin tissue has hardened into biological armor as tough as bone.

Danger: It deflects firearm shots or cold weapon strikes from the front. Since the shock-absorbing cell layer beneath the armor perfectly protects the head, a frontal weak point attack is impossible unless the biological armor is first stripped away using traps or heavy weapons.

── CHAPTER 5. The Tiny Fraction of Humanity in Korea: 5 Types of Immunity Classification (IMMUNITY)

Now that the majority of the population has turned into corpses, there exists a very small number of humans who resist the virus through a miracle of genetic sequencing. Their antibody resistance methods are strictly classified into five forms.

TYPE 1. Incomplete Single-use Immune: Upon the first exposure to infection, they forcibly suppress the virus to avoid immediate death. However, there is a high probability of death from shock due to high fever exceeding 40 degrees and pain for 48 hours, and even after recovery, serious permanent sequelae such as chronic motor impairment or tinnitus remain. It is a one-time antibody that results in confirmed infection if bitten again.

TYPE 2. Complete Single-use Immune: Upon initial infection, the virus is completely destroyed without any symptoms or sequelae. However, since it is only a one-time shield, if they overconfide in their constitution and are exposed to a second source of infection, the immune system immediately collapses and they 100% rapidly turn into an infected entity.

TYPE 3. Incomplete Multiple Immune: They do not turn into zombies even if bitten multiple times or if body fluids enter. However, every time the virus invades, the antibodies in the body clash violently, causing fatal chills, coughing up blood, and shock-level pain each time. Organs age rapidly with each occurrence, and they usually die due to immune system limits after five or more cumulative contacts.

TYPE 4. Complete Multiple Immune: An exceptionally rare constitution that is hard to find, maintaining a perfect asymptomatic defense state without pain or transformation even after multiple exposures. However, this antibody causes extreme rejection when fused with another person's blood, making it impossible to use as a material for a universal vaccine. It is a personal-specific immunity lived with the loneliness of being unable to save others.

TYPE 5. Absolute Immune (Ultra-rare in Korea): The master key to civilizational reconstruction, with only 10,000 existing worldwide. In addition to permanent immunity, infected entities mistake them for 'fellow zombies' thanks to a specific hormone secreted from their cells. They are a key asset capable of tactical operations such as luring or bypassing infected entities, as they are not attacked first even when walking through the middle of a zombie herd.