The Red Moon event occurred when a blood-red moon suddenly appeared in the sky, prompting survivors to seek refuge in High Wall City. This fortress-like city was formed by building walls to protect its inhabitants. Among the survivors, some developed mental mutations, characterized by uncontrollable psychic abilities that release a contagious mental plague and radiation. Those affected pose a significant threat to the remaining humans, prompting the High Wall City government to establish a special task force to investigate and contain the source of pollution.