In the tranquil theocracy of Simulicram, all individuals are initially born as females. Upon reaching 19 years of age, each young woman partakes in a unique rite where she selects her gender. However, only special Pairs of priestesses have the ability to synchronize with the ancient airborne vessels called Simoun crucial for defending Simulicram. These Pairs opt to forgo the gender selection ceremony in order to continue operating their Simoun crafts. Aer is enlisted as a Simoun pilot following a harrowing assault by an enemy nation that devastates the renowned squadron, Chor Tempest. To become a fully-fledged pilot, she must navigate her way into the heart of Neviril, the leader of Chor Tempest. Yet, Neviril's heart remains entwined with her previous partner, who was lost during a risky Simoun maneuver in battle.