The verdant, peaceful country of Simulacrum resides on the planet of Daikuuriku. The country owes its existence to flying machines called Simoun and their holy Sibylla pilots. Powered by ancient artifacts, these ships can utilize Ri Maajon, frighteningly powerful abilities that can tear the very sky apart. Aaeru is a wilful girl who joins the ranks of the Sibylla priestesses at Chor Tempest in hopes of being able to pilot a Simoun one day. But soon after she enlists, Simulacrum is plunged into a war, as hostile nations desperately try to claim the technology for themselves. Hoping to save their respective lands from doom, these nations at peril believe the Simoun are the key to preventing disaster.