Jin-hee is an elementary school girl whose overworked parents feel guilty for not spending enough time with her, so they send her ahead to her maternal grandfather’s house in the countryside for summer vacation. Excited by the wide-open fields and green hills, Jin-hee tries to enjoy her holiday but discovers an awkward distance with the grandfather she hasn’t seen in a long time. While chasing a fluttering butterfly into the forest, she gets lost and meets a round-faced “watermelon seed” spirit that has also lost its way, and the two decide to find their way home together. Along the journey, they encounter a gigantic cracked watermelon that becomes a “watermelon swimming pool,” fireflies in the night sky, and the quiet kindness of village neighbors. Through this adventure, Jin-hee learns that children, parents, and grandparents are all precious to one another, and that she herself is a shining, irreplaceable part of her family.