Clinging to an unfinished letter written by her recently deceased father, young Momo moves with her mother from bustling Tokyo to the remote Japanese island of Shio. Upon their arrival, she begins to explore her new habitat, meeting local children and learning their routines and customs. However, it's not long before several bizarre occurrences crop up around the previously tranquil island. Orchards are found ransacked, prized trinkets start disappearing and, worst of all, each morning after her mother leaves for work, Momo hears strange mumblings coming from the attic of their home. Annoyed by these creepy goings-on and her mother's refusal to believe them, Momo embarks on a strange and supernatural adventure to discover the source of the mischief, which leads her to a trio of troublesome imps: the flatulent lizard Kawa, the childlike Mame and their hulking ogre leader Iwa. Momo also learns that her visit to the island is in some way connected to her father's mysterious letter. 《写给桃子的信》：人生需要跳水的精神。被野猪追过的夏天。给父亲的信。信。阿豆是不是桃子的爸爸。写给桃子的信。momo 要长大哟。最好的夏天，谢谢你陪伴。写实日常与幻想喜剧的平衡。来自汐岛的潮起潮落声——洼田美奈与《给桃子的信》。 11岁的小学6年级女孩宫浦桃子（美山加恋 配音）在父亲意外去世后，随母亲郁子（优香 配音）从东京迁到了濑户内海的汐岛。忙碌的母亲无暇顾及桃子，令桃子在新环境中时常感到孤单无助。桃子一直保留着父亲只写下了“给桃子”这样开头的一封信，但是始终无法明白父亲想要通过信件传达给她的话 。 初到汐岛，桃子打开了阁楼里一个装着描绘妖怪画册的旧盒子，从此开始察觉到身边一连串不可思议的事情。“汐岛上一定存在着什么东西”，怀抱着这样想法的桃子，在汐岛奇异而热闹的夏天里邂逅到的竟会是……？ 本片由日本知名动画公司Production I.G制作，是《人狼》导演沖浦啓之睽违多年的温馨治愈之作。
