Shibuya Kazuya, a 24-year-old temp worker, one day receives a mass email. The email is a recruitment notice for a government-sanctioned survival killing game called <Savanna Game>, with the entire nation of Japan as its battlefield. Though initially bewildered, after confirming its authenticity, Kazuya decides to participate, teaming up with his classmate Furukawa Jin and childhood friend Kudo Mafumi. Their equipment includes the special mobile terminal "SG" provided by the "Savanna Game Management Committee," various lethal "equipment," and "Skill Seeds," the source of supernatural abilities. Kazuya receives the "Dark Blade," Jin gets the "Claws That Tear Through Space-Time," and Mafumi is granted the healing skill seed "Magical Heal." While trembling at their first acts of killing, they gradually become immersed in the battles. Along the way, they are joined by a middle-aged man named Igarashi Kensuke, who possesses the "Air Gum" equipment, and somehow manage to survive the first round. During the fight, they meet the handsome Fujiwara Yu, also known as Okita Sōji, and with the help of Hijikata Toshizō from the "Shinsengumi" led by Kondō Isami, and Himiko, they undergo training and learn that this era is a parallel world. The second round is set to be the American Civil War, with the North centered around the "Shinsengumi" and the South appearing to revolve around the mysterious group "Black Bandits," to which Seth Linda—who killed the Shinsengumi's Yoshitsune—belongs. Having newly acquired the first-round victory bonus items—"Hell Chain Gauntlets," the "High-Mobility Multipurpose Wheeled Vehicle Humvee," and "Dog Suit" with canine senses of smell and hearing—the four are joined by their friend Kirino Gorō as they prepare for the new battle. The death game has only just begun...