In a world where certain humans command mighty supernatural duos called Daemons, it is the birthright of "the children who sunder day and night"-twins Yuru and Asa-to rule over these powerful entities. Separated from a young age and unaware of the truth of their birth, brother and sister must fight to make their way back to each other, claim their birthright, and save the world. Yuru's quiet life comes to a sudden, bewildering end when his mountain home is attacked...by none other than his twin sister Asa! Forced to assume the role of Daemon Wielder, Yuru manages to escape with the help of his new allies. But while they seek to keep him hidden, Yuru seeks answers, a search that puts him on a collision course with Asa and her mysterious co-conspirators, the Kagemori clan.