Simoun: Shoubi Sensou - Fuuin no Remersion

Simoun Shoubi Sensou Fuuin no Remersion: Tells the story of a group of girls who pilot mighty airships to defend their nation against would-be usurpers. In the world of the Simoun, all children are born female but decide their final sex at age 17. In the animated series, a nation known as Argentum invades Simulacrum and the Simoun are sent into war to protect the homeland from the attackers. Since the girls are almost of age but their skills are needed to wage war, they are granted an extension upon which to decide their sex.