It has been six months since Yoshiki Tsujinaka's best friend, Hikaru Indou, went missing in the mountains and returned a week later with no recollection of what had transpired. Certain that it is not the Hikaru he knows who came back, Yoshiki finally asks Hikaru about it. Suddenly, "Hikaru" reveals his true monstrous form and begs Yoshiki to keep it a secret, as he does not want to kill him.
Despite his paranormal nature, "Hikaru" seems almost innocent, full of childlike wonder and eager to experience the summer heat, the countryside, and all kinds of other things in a human body for the first time. And for Yoshiki, it matters little if "Hikaru" is a fake relying on stolen memories—as long as he never leaves again. As Yoshiki desperately clings to "Hikaru" in his intense grief, it becomes increasingly clear that something dangerous and supernatural may have descended from the mountains into their village.
