Tide is dead." After hearing the news of the death of his childhood friend, Ushio Kobune, Shinpei Amishiro returned to his hometown, Hitogashima, Wakayama City, for the first time in two years. He is reunited with his family and friends. The funeral ceremony goes on without a hitch. However, Shinpei's best friend, Hishigata Window, tells Shinpei that there is something suspicious about Ushio's death and that there is a possibility that he was killed by another person. The next day, an incident occurs in which a neighboring family suddenly all disappear. At the same time, Shinpei hears an ominous rumor. He hears an ominous rumor: "Anyone who sees a shadow that looks just like him will die. The shadow will kill you." Furthermore, Mio, Ushio's younger sister, claims that she saw a shadow three days before her sister's death. A time-traveling sci-fi suspense now opens on a small remote summer island in the Kitan Strait. (ref: https://summertime-anime.com/)