Simoun  

シムーン

In Daikuuriku's world, everyone is born female, but at age 17, they can choose to become male or remain female. The peaceful theocracy of Simulacrum is protected by magical flying machines called "Simoun", which are only operated by young girls who have not yet chosen their sex. These Simoun possess a powerful ability known as "Ri Maajon" that can destroy large numbers of enemies at once. When the industrialized nation of Argentum decides to invade Simulacrum for its secret, war breaks out, drawing the Sibyllae (priestesses who fly the Simoun) into a lopsided battle. Due to the conflict, the Sibyllae are granted an exemption from choosing a permanent sex as long as they continue flying. Aaeru, a determined young Sibylla with a mysterious past, and Neviril, leader of Chor Tempest, Simulacrum's elite Simoun squadron, must lead their fellow priestesses through both internal conflicts within their ranks and external battles in the sky.