Following her father's sudden passing, 11-year-old Momo Miyaura relocates from bustling Tokyo to a secluded island in Seto Inland Sea with her mother. Clutching an incomplete letter bearing the words "Dear Momo" left by her father, Momo grapples with its emotional weight. As she navigates the quaint town with its antiquated structures, tranquil fields, and enigmatic shrines, Momo reluctantly acquaints herself with her new surroundings. A chance attic exploration leads her to a tattered picture book on youkai, triggering a series of peculiar events and the appearance of three mischievous youkai. Through these encounters, Momo unravels the challenges of her peculiar existence, all while seeking closure on the enigmatic message from her father in Momo e no Tegami.