In a post-apocalyptic Earth overrun by monsters and demons, Kakugo and Harara are trained in the ancient Zero fighting technique by their father to protect humanity's last survivors. Clad in living armor crafted from ancient warriors' souls, they venture out to defend the weak against savage attacks. When Harara succumbs to darkness, killing their father and believing Kakugo dead, a brutal reunion awaits. Kakugo emerges in a city, saving humans from cannibalistic beasts and twisted mutants, only to face his deranged sibling in a bloody showdown that redefines sibling rivalry in the 21st century.