Earth has had an element called "light traces" since ancient times, and traces of this substance are in the air. A moderate amount of light marks can help genetic evolution and accelerate the survival of species. But in excess, unpredictable mutant organisms can be produced, often resulting in dramatic changes in species distribution.

It happened in Pontrigio, a high-tech country that was "nuclearized" by the coalition forces due to some changes. After the nuclear bombing of the land, a large number of light traces were detected like a volcanic eruption, and the people called it "the wrath of the earth". In order to solve the increasing number of mutants and mutant creatures due to the rising concentration of light marks, the government has launched the "Xilang Project": the living area will be raised to a thousand meters in the air, away from the light marks on the surface.

There is a lack of various materials in the high sky, the most serious thing is energy. Fortunately, scientists have found that light traces can be used as a new energy source that does not lose nuclear energy. But you need to go to the dangerous old surface to defeat mutant creatures to get it. So the government began to recruit and train "light collectors", an emerging profession specializing in expeditions to the old surface and collecting light marks for the government to exchange for money. Players need to form a team of three light collectors to advance to the dangerous old surface.