Shirō, a third-year junior high student, navigates daily life with school friends in Minami Shimabara city, Nagasaki—a place simultaneously his home and a historical site echoing the early Edo period's Shimabara Rebellion. His personal circle includes an older childhood friend, Akane, who returns from Tokyo each summer, and a longtime companion named Tokiya. After Akane's arrival, Shirō accompanies both friends on a hometown walk where shared memories intertwine with budding emotional tensions. This ordinary excursion fractures when a diminutive, enigmatic creature called Goron manifests before them. Shirō's confrontation with Goron ruptures the fabric of his routine existence, igniting cascading unexplained phenomena across Minami Shimabara.