In the world of Daikuuriku, everyone is born female, and chooses which sex they wish to become at age 17. In this world, the peaceful theocracy of Simulacrum is guarded by magical flying machines called “Simoun”, which can only be piloted by young girls who haven’t chosen a sex yet. The Simoun can activate a magical power known as “Ri Maajon” that can destroy large numbers of enemies at once.