Twins Yuru and Asa have never shared a single day: he lives by daylight, she only after dark. That arrangement ends when soldiers storm their isolated village and Asa is left for dead. A wandering stranger named Dera pulls Yuru from the wreckage and summons spectral daemons to fight back, and a woman claiming to be his real twin sister appears in Asa's place. The two set out to learn who attacked the village and why Asa's identity is suddenly in question.