Immune Simulator is a strategy-adventure game. The story describes a world in which humans are fighting against zombies and losing. The female protagonist accidentally finds an old computer with software that records the process of human-zombie conflicts, much like historical documents. The protagonist attempts to operate the computer and view these historical records but discovers that the historical data can be changed. After leaving the machine, the balance of power between humans and zombies in the real world also changes. Just as she thinks she can use this machine to turn the tide against the zombies, her companions begin to change one by one. Is this machine a salvation from God or a trap from the devil? What secrets are hidden in this machine? It's up to the player to discover.