During a summer holiday at her grandfather's home, six-year-old Hotaru Takegawa wanders off in a forest rumored to be home to spirits. As she cries out in despair, Gin—a mysterious boy wearing a mask—approaches her and offers assistance. Thrilled to see another person, Hotaru runs toward Gin with open arms, only to be sharply pushed away. She soon discovers the serious reason for his reaction: Gin is under a terrible curse. If a human touches him, he will vanish forever. Although Gin tells her never to come back, Hotaru does the opposite, and before long, the two grow close despite his fragile condition. Still, as time goes by and their feelings for each other deepen, Hotaru and Gin begin to struggle with the limits that fate has placed between them.