The lush, tranquil nation of Simulacrum is situated on the planet Daikuuriku. Its survival depends on flying vessels known as Simoun and their sacred Sibylla pilots. Driven by ancient relics, these craft can harness Ri Maajon, terrifyingly potent abilities capable of rending the sky itself. Aaeru is a determined girl who enters the ranks of the Sibylla priestesses at Chor Tempest, hoping to eventually pilot a Simoun. However, shortly after her enlistment, Simulacrum is drawn into war, as rival nations desperately attempt to seize the technology. Believing the Simoun to be the key to averting catastrophe, these nations, facing peril, hope to save their own lands from ruin. Now fighting their foes and coping with personal tragedies, the girls of Chor Tempest must adapt to their circumstances if they wish to uncover the mysteries at the core of their country: the Simoun and the Ri Maajon.