In a secluded village, twin siblings are born, their lives divided between day and night. Years pass, and the elder brother Yuru works as a hunter of animals, while his sister Asa remains confined to a cage, assigned a special task that prevents her from meeting anyone beyond a chosen few.
One ordinary day, armed men arrive in helicopters—referred to by the villagers as "dragons"—and attack the settlement, killing every adult they see as they search for Yuru. As Yuru tries to reach Asa to escape together, he discovers only her corpse; moreover, the person who killed her claims to be Yuru's actual twin sister.
Before this woman can seize him, Yuru is saved by Ryuu "Dera" Tadera, an outsider who often visits the village. Soon, however, the two find themselves cornered. As a final resort, Dera has Yuru present an offering to the village's deity, summoning a pair of daemons whose very existence is destined to unveil the truth behind the turmoil.