The Tradition of the Sea.As Akari is scolded by her father for disobeying the village's rules, Hikari reminisces about how she always took care of him after their mother's death, and is later informed by Akari that she decided to break up with her boyfriend. While visiting their old school building, the boys plan how they will confront Itaru about his relationship with Akari. While waiting for them in the music room, Chisaki asks Manaka if she likes Tsumugu. Manaka replies that she isn't sure. Not realizing that the boys can overhear just outside the room, Manaka wonders if she would go out with Tsumugu and if they would kiss; and if she would one day get married and have to leave the village. After hearing this, Hikari walks in acting as though he hadn't heard any Manaka's confession. The next day, Hikari confronts Itaru and follows him up to Tsumugu's house where he is stopped by Tsumugu's grandfather, who explains to them that aside from the bad mood with the inhabitants of the surface, people from the village are not allowed to marry those from outside as their children will be born without ena. The children become unable to survive underwater and thus the former inhabitants are forced to leave Shioshishio to raise them. Hikari discovers that Tsumugu's grandfather also came from the village. On the next day, Hikari stops being hostile to Tsumugu and he becomes friends with the rest of the group after they finally complete the offering together. Knowing how much she is suffering with their separation, Hikari decides to make amends with Akari's boyfriend, but is stopped by the two girls who fought him before and one of them reveals that said man is her father.