The narrative is set in Japan. The year is 2030, and the Earth has been entirely overrun by a viral sickness known as "Gibia," which transforms affected individuals into diverse monsters dependent on their age, gender, and race. A samurai and a ninja from the early Edo era travel through time together and arrive in a destroyed Japan to assist a professor working on a viral cure. On their trek to redeem mankind, they face many Gibia monsters, outlaws, and other ferocious opponents.