In the future, the Japanese government captures a class of ninth-grade students and forces them to kill each other under the revolutionary "Battle Royale" act.
After being used and betrayed by the detective she had fallen in love with, young Matsu is sent to a female prison full of sadistic guards and disobedient prisoners.
In the outskirts of Tokyo, a poor but close-knit group living on the fringes of society survives through shoplifting and odd jobs. When Osamu and his son take in a neglected young girl, their already fragile existence begins to unravel. As the family grows attached to her, buried secrets surface, forcing them to confront the true meaning of love, belonging, and what makes a family.
In Tokyo, Japan, several grotesque murders take place on rainy days. Detective Sawamura, who is in charge of the case, soon discovers that his own family is connected to the crimes.