A fantasy inspired by the legend of Urashima Taro, who is said to have spent decades living in an undersea realm. Set on the Shonai Peninsula in Kagawa Prefecture, it presents a dream-like depiction of a young man's recovery from the death of a friend. University student Taro nearly drowns in the sea on a visit home but is rescued by his close hometown friend Masahiko, who instead loses his own life. Taro is wracked with guilt. Then one day, a strange girl named Mizuki appears before him.