Hisako is an elderly artist living in the coastal town of Kissakibetsu, famous for her paintings of the local salt marshes and the Marsh House. She first meets Anna when both choose the same spot to create art; Hisako paints while Anna sketches. Hisako compliments Anna's skill and observes a resemblance in her sketches to a girl named Marnie from her youth. She informs Anna that the Marsh House has been bought and will be renovated, leading to Anna meeting the new resident, Sayaka. Later, after Anna recovers from illness, Sayaka shows her a painting found in the Marsh House. Hisako recognizes it as her own work, gifted to her childhood friend Marnie. She agrees to tell Marnie's story to Anna and Sayaka. Hisako confides that despite Marnie's wealthy family, she suffered neglect from absent parents and abuse from her governess and maids. Marnie married their mutual friend Kazuhiko and had a daughter, Emily. After Kazuhiko's death, a grief-stricken Marnie entered a sanatorium and sent Emily to boarding school due to lacking other caregivers. Hisako recounts that Emily returned as a resentful teenager, their relationship remaining broken. Emily eventually ran away as an adult, had a daughter (Anna), and died with her husband in an accident. Marnie then cared for her infant granddaughter but passed away when the child was about two, leading to the granddaughter's foster care. Unaware Anna is that granddaughter, Hisako's story reveals Anna's biological family: Marnie was her grandmother and Emily her mother. Her name, meaning "long time child," connects her to Kissakibetsu's history. In the original novel, she is known as "Gillie." As a local historian and artist, she bridges past and present, aiding Anna's understanding of her origins. Before Anna leaves Kissakibetsu, she introduces her foster mother, Yoriko, to Hisako.