Momo is an 11-year-old girl who, following the recent death of her father, moves with her mother from Tokyo to live in her grandparent's old house on Shio, a small remote island, where her mother was born and grew up. She keeps an unfinished letter he father wrote to her. Initially unaccustomed to her new rural surroundings, a turning point comes when, exploring the attic, she discovers an old book and strange events occur, such as the appearance of three odd creatures, the yokai, which only Momo can see.