In the wake of the 21st century, Earth has been left in shambles, overrun by monsters and fiends that hunt humans for sport. In an effort to protect what remains of humanity and instill hope for the future, Kakugo and Harara were trained in the ancient Zero combat style by their father. With the aid of armors crafted from the souls of fallen warriors, they employ their superior fighting abilities to defend the defenseless against brutal attacks. Despite their careful preparation, Harara succumbs to the darkness within, killing their father and believing Kakugo to be dead as well. As fate would have it, the two siblings' paths converge once again when Kakugo journeys into a ruined city to safeguard the few remaining inhabitants from flesh-eating mutants. While Kakugo fights to preserve life, his twisted sibling resurfaces, leading to the most brutal fraternal conflict of the century.