The Promised Day.Five years later, the sea over Shioshishio is frozen and the surface enters into a continued winter. Chisaki pays a visit to Tsumugu's grandfather Isamu at the hospital before returning to meet Akari and her son, Akira. They reminisce about Miuna cheering up Akari up after she had found out that she was pregnant and was too worried about Hikari and the others to be happy with it. At the school, the students are informed that a Tomoebi will occur over the sea and they decide to have a party at the shore. Sayu warns Miuna that one of their classmates intends to confess to her on the occasion. After the Ofunehiki five years ago, Chisaki was taken in at Tsumugu's house by Isamu. Later Isamu is hospitalized and Tsumugu leaves to study oceanography at college to learn more about the situation at the sea villages and their connection with the climate changes. During the Tomoebi, Miuna is asked out by her classmate, but she declines claiming that she likes someone else. A strange light appears and Tsumugu, who is studying the phenomena with his teacher, meets Miuna at the place where the light appears and nearby they find a naked Hikari, who has not aged since he disappeared five years ago.