Plot
Following the death of her father Kazuo, Momo Miyaura and her mother Ikuko travel from Tokyo to the Seto Inland Sea. Momo carries Kazuo's unfinished letter, which contains only the words "Dear Momo". At her mother's estate in Shio Island (汐島, Shiojima), they meet their relatives Sachio and Sae Sadahama, and Koichi, a postman and an old friend of Ikuko, who has always had a crush on her. Momo is devastated and misses Tokyo. In the attic, she opens a present containing a rare picture book about goblins and Yōkai, collected by Sachio's father. Three droplets from the sky enter Ikuko's estate and transform into yokai consisting of Kawa, Mame, and Iwa, the group's leader.
When Ikuko begins taking nursing classes, Momo reads the book and begins to hear some strange sounds from the house. She is chased out of the estate by the yokai, only to encounter a young boy named Yota. Oblivious to the house's strange noises, Ikuko and Yota assume that it is safe. The next morning, she meets Yota and his sister Umi. The three meet up with his friends and swim under the bridge, but Momo decides not to and runs to a shelter during a thunderstorm. Iwa, Mame and Kawa reveal themselves, having stolen some fruit from around the island. Frightened, Momo runs back to Ikuko's estate and discovers that Sachio's orchard was ransacked. Sachio then tells Momo that the yokai were originally gods, but they were transformed as a punishment for breaking the divine laws.
Momo attempts to prevent the yokai from stealing the local vegetables, but Kawa inadvertently breaks Ikuko's mirror. After a brief argument with Ikuko, a distraught Momo leaves and talks to the yokai about her relationship with Kazuo as well as the events leading up to his fatal boating accident. Later, Ikuko suffers a near-fatal asthma attack while searching for her. Momo, realizing her mistake, desperately asks the yokai to help look for a doctor on the other side of the island. The yokai, however, decline and Momo personally searches for the doctor. As Koichi and Yota pursue Momo, she reveals her previous argument with Kazuo before his death and asks Koichi to help find the doctor. Meanwhile, the yokai realize they can escape punishment by allowing Momo and Koichi to cross over the newly completed bridge and find the doctor.
The next morning, Momo writes a letter to her father thanking him as Ikuko recovers. Having completed their mission to protect Momo, Iwa, Mame and Kawa transform back into the droplets and return to the sky. That night, Momo and Ikuko reconcile during the tōrō nagashi and the two realize that Kazuo wrote that he was proud of her. She begins her new life with Yota and the other children by swimming under the bridge.
