Noboru Kuroda is a 13-year old boy who believes that life is empty and meaningless. He finds a hole into the wall between his room and his mother's room and uses that to spy on her. He kills a kitten with a group of friends who share his worldview and feels that the act was transformative. He sees Ryuji as a hero and a real man—until he gives up the sea and is soft about punishing Noboru when they find the hole in the wall. Then Noboru complains to his friends. Together, they decide to drug and kill Ryuji.

Fusako Kuroda is Noboru's mother. She is young and widowed. Fusako works hard and enjoys tennis and embroidery. She falls for Ryuji, a sailor, but isn't sure whether she wants to be in the relationship. She doesn't want to constantly be left by him when he returns to the sea. When he proposes, she happily accepts.

Ryuji Tsukazaki is a sailor who falls for Fusako. He's torn between a life on the land and the romance of the sea. His love for Fusako and the repetitiveness of a life on the ship lead him to offer her his money and his hand in marriage. She agrees. However, Noboru is offended by his actions and disappointed in him. Ryuji is led by the boys to the sea where he talks about his dreams and drinks the poisoned tea they drugged.

The Chief is a friend of Noboru's and the leader of the gang of boys. He's the one who dissects the kitten and the one who decides that the boys need to ultimately murder and cut Ryuji apart at the end of the story.