Simoun: Shoubi Sensou - Fuuin no Remersion

A war breaks out between three nations Simulacran, Argentum, and Plumbum over Simulacran's helix motor technology that powers the airships known as Simouns. Two fleets of the Simoun, Chor Caput and Chor Tempest, stumble upon a huge Argentum airship fleet attempting steal a Simoun. Suffering massive losses in the battle, the pair Neviril and Amuria of Chor Tempest attempt an extremely powerful but extremely dangerous maneuver out of desperation named the Emerald Ri Majon; Neviril hesitates after making eye contact with the enemy, and the pair fail resulting in an explosion that takes Amuria with it. The fight leaves the sibyllae or members of Chor Tempest extremely demoralized and Neviril in despair.

Résumé

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.