The story is set in the world of Island. One day, mysterious machine-like creatures known as “Plantum,” whose origins are unknown even to the Source, suddenly invade. Though their appearances vary, all are covered in platinum-like shells. Nations across the world mobilize their full military forces, yet are completely defeated within a single day. As the Plantum expand outward in a circular pattern, people are forced to abandon their homes and evacuate continuously. Over the course of two years, governments become dysfunctional, social order collapses, crime and gangs run rampant, and violent conflicts erupt over limited resources. The world gradually descends into an apocalypse. To contain the spread, the government establishes the “Rift Zones,” divided into three types: the “Destruction Zone,” which has been completely devastated and is uninhabitable; the “Red Zone,” where survival is still barely possible but constant threat remains; and the “Fringe Zone,” which is predicted to be invaded within one month. Those struggling to survive in these areas are known as “Rift Walker.”