Battle Royale takes place in an alternate timeline—Japan is a member region of a totalitarian state known as the Republic of Greater East Asia. Under the guise of a “study trip”, a group of students from Shiroiwa Junior High School in the fictional town of Shiroiwa, in Kagawa Prefecture, are gassed on a bus. They awaken in the Okishima Island School on Okishima, an isolated, evacuated island southwest of Shodoshima (modeled after the island of Ogijima). They learn that they have been placed in an event called the Program. Officially a military research project, it is a means of terrorizing the population, of creating such paranoia as to make organized insurgency impossible.
The first Program was held in 1947. According to the rules, fifty third-year junior high school classes are selected (prior to 1950, forty-seven classes were selected) annually to participate in the Program for research purposes. The students from a single class are isolated and are required to fight the other members of their class to the death. The Program ends when only one student remains, with that student being declared the winner. Their movements are tracked by metal collars, which contain tracking and listening devices; if any student should attempt to escape the Program, or enter declared forbidden zones (which are randomly selected at the hours of 12 and 6, both a.m. and p.m.), a bomb will be detonated in the collar, killing the wearer. If no one dies within any 24-hour period, all collars will be detonated simultaneously and there will be no winner.
After being briefed about the Program, the students are issued survival packs that include a map, compass, food and water, and a random weapon or other item, which may be anything from a gun to a paper fan. During the briefing, two students (Fumiyo Fujiyoshi and Yoshitoki Kuninobu) anger the supervisor, Kinpatsu Sakamochi, who kills both. As the students are released onto the island, they each react differently to their predicament; beautiful delinquent Mitsuko Souma murders those who stand in her way using deception, Hiroki Sugimura attempts to find his best friend and his secret love, Kazuo Kiriyama attempts to win the game by any means necessary (stemming from his lack of ability to feel human emotion due to a brain injury sustained in a car crash while in utero) and Shinji Mimura makes an attempt to escape with his best friend Yutaka Seto.