Last Updated September 5, 2023.
Themes in The Sailor Who Fell From Grace With the Sea include family, punishment, and ideals.
Ideals play a large role in the story. Noboru has an idea of who he wants his mother's boyfriend to be—a masculine sailor and hero. Ryuji himself wants to be that man to some extent but also recognizes the reality of a life at sea; he knows that he will be bored and lonely. Noboru's mother is scared of the stereotypical life of a sailor's woman. She doesn't want to be constantly left. Ryuji is able to give up the dream of a life at sea for a life with her, but Noboru can't let go of the feeling of betrayal he gets from Ryuji when the man doesn't live up to his ideals.
Punishment is another major theme in the book. Noboru uses his peephole on nights that his mother punishes him. The boys in Noboru's group decide that they need to punish Ryuji for deciding to marry Noboru's mother and become his father. This is after Ryuji decides that he and his fiancee don't need to punish Noboru for the peephole; Noboru respects him less for the leniency. The boys ultimately murder Ryuji for these supposed crimes.
Family is another important theme. Noboru's father is dead and he hates the idea of Ryuji taking on such a role. His mother is unable to control him and he constantly lies to her and deceives her. When they decide to create a new family, Noboru takes that possibility away by plotting and participating in the murder of Ryuji.