The story takes place in Japan in the year 2030. 　　 A virus is spreading across the world. Those infected by the virus mutate into monsters, with the forms varying based on age, gender, and ethnicity. Due to the diversity of these transformations, the virus is called "Gibia" (like the rich variety of wild birds and beasts). 　　 However, in this wasteland of Japan, a samurai and a ninja suddenly appear. Having traveled through time from the early Edo period, the two of them join forces with a doctor researching a cure for the virus and embark on a mission together. 　　 Faced with waves of attacking Gibia, desperate outlaws who plunder food from passersby, and sieges from various enemies, a perilous, life-or-death adventure begins.