Michiru Aizawa

In the peaceful theocracy of Simulicram, everyone is born female. At age 17, each maiden undergoes a special ceremony where she chooses her sex. However, only Pairs of maiden priestesses can synchronize with the ancient flying ships known as Simoun needed to defend Simulicram. These Pairs refrain from undergoing the ceremony as long as they wish to keep piloting their Simoun. (myanimelist.net)