Anna had no friends in this world because she suffered from asthma and was always quiet, unable to get along with anyone in her class. This led the doctor to suggest to her family that they move to a quiet place for Anna's comfort. Her mother sent her to Sapporo Village after they moved to the countryside. Anna spent her time walking, exploring the area, and drawing. Then she found herself drawing a seemingly abandoned house that stood on the water. This house was only accessible at low tide. That's when she met Marnie.
Although Marnie was the first girl her age she had met in the village, she asked Anna to keep her secret from everyone else. There are many mysteries surrounding Marnie.