The starting point of the catastrophe: In 2073, a "source wave" impact occurred simultaneously around the world. The source was unknown (not alien invasion, not nuclear pollution). It could not be captured by instruments and had an impact only through human perception.
Core hazard: "Source Wave" distorts human five senses (mainly vision, hearing, and touch), causing "subjective perception" to break through the boundaries of reality - human fears, memories, and hallucinations will materialize and form "virtual images", which only cause harm to people who can "perceive" them (for example: the "fire" virtual image seen by A will only burn A, but will have no effect at all if B cannot perceive it).
Virtual image classification:
Level Ⅰ "Afterimage": brief flash of visual/auditory interference (such as hearing non-existent footsteps), no real harm;
Level II "Obsession": generated by strong emotions (fear, longing), with basic interactivity (such as the "black shadow" chasing people), contact will cause minor physical damage (abrasions, bruises);
Level III "Domain Master": generated by a large number of human collective memories (such as the "ghosts of old residents" in abandoned cities), able to construct a small-scale "perception domain" (those who enter the domain will be forced to see the same virtual image), and can cause extremely high damage (fractures, organ damage);
Level IV "Source Shadow": A legendary virtual image, suspected to be directly related to the source of the "Source Wave". It only appears in Shenwu District, and there are currently no surviving sightings.
