Life in Tokyo in the year 2020 is harsh, with high crime rates and offenses against women ranking second only to murder. To shield their daughter from such dangers, Tsukasa's parents raised her as a boy. Tsukasa dreams of becoming a police officer to fight the yakuza, following in her parents' footsteps. However, her parents died in the line of duty, leaving Tsukasa and her three brothers to survive on their own. Consequently, Tsukasa works as a bodyguard for her classmate Ryuji, who is the leader of Tokyo's most powerful yakuza syndicate, in order to pay off the family's debts.