In the distant future, the world is corrupted by The Fallen. These entities, arising from the unknown, possess creatures and humans without warning, causing mass chaos. In response, an organization was formed from death row inmates, each given a device called a "Clock." However, when their timer runs out, their original sentence is carried out. To stay alive, they must kill The Fallen. The higher the rank of the fallen creature they vanquish, the more time gets added to their clock. This system has transformed survival into a game for these criminals, all vying for more time. This is Gun-Game!