Etsuko is a Japanese woman who immigrated to England with her English second husband and her older daughter, Keiko. Following Keiko's recent suicide, Etsuko spends much of her time reflecting on a specific summer in post-WWII Nagasaki. In her memories, she is a dutiful wife trying to rebuild her life after losing her original family to the atomic bombing, quietly observing her mysterious new neighbor while pregnant with her first child.

Sachiko is an aristocratic woman who falls on hard times following the war and the death of her husband. She lives on the outskirts of Nagasaki with her daughter, Mariko, whom she frequently neglects. Desiring to escape the rigid constraints of traditional Japanese society and reclaim her former affluent lifestyle, she pins her hopes entirely on immigrating to America with her foreign boyfriend.

Jiro is Etsuko's first husband and a traditional Japanese salaryman. Fastidious about his appearance and stern in his expression, he dedicates himself entirely to his career while expecting his wife to manage the domestic sphere alone. He maintains a distant, emotionally detached presence in his home and frequently dismisses his father's attempts to connect with him over chess games or conversation.

Niki is Etsuko's younger daughter, born to Etsuko's English second husband. Living a modern, Western lifestyle in London with her boyfriend, she contrasts sharply with her mother's traditional Japanese background. She views her mother's immigration as an act of courageous rebellion, though she possesses a highly idealized and limited understanding of Etsuko's actual history.

Keiko is Etsuko's eldest daughter, born during Etsuko's first marriage in Japan. Having moved to England with her mother at the age of seven, she struggles deeply to adapt to her new environment. She eventually becomes intensely reclusive, shutting herself off from her family and moving away to Manchester before taking her own life prior to the start of the narrative.

Mariko is Sachiko's young daughter, an unfriendly and isolated child who spends much of her time unsupervised around the riverbed. She exhibits signs of trauma, frequently speaking about a mysterious woman she claims visits her at night. Mariko stubbornly resists her mother's plans to move to America and feels an intense, protective attachment to her pet kittens.

Ogata-san is Jiro's father and a retired school director who took Etsuko in as an orphan after the atomic bombing of Nagasaki. He represents traditional Japanese values, believing firmly in duty, loyalty, and the old educational system he helped build. He struggles to reconcile his past life's work with the harsh criticisms leveled against his generation by younger educators in the post-war era.

Frank is an American living in post-war Japan who is romantically involved with Sachiko. Described as tall and balding, he promises to help Sachiko and Mariko immigrate to the United States. He frequently disappears for stretches of time and drinks heavily, displaying a clear pattern of unreliability that threatens Sachiko's plans.

Mrs. Fujiwara is an older woman in Nagasaki who runs her own noodle shop. Having lost much during the war, she rebuilds her life by starting a business, which she considers a point of immense personal pride. She kindly offers employment to Sachiko at Etsuko's request.

Shigeo is a younger man and former student who used to visit Ogata-san's home before the war. He recently publishes an article in an education journal criticizing the older generation of teachers, blaming their traditional methods for Japan's disastrous involvement in the war.

David is Niki's boyfriend who lives with her in London. He shares Niki's modern, Western lifestyle, standing in sharp contrast to the traditional family structures Etsuko knew in Japan.

Nakamura-san was Etsuko's early love interest in Nagasaki. He passes away during the atomic bombing along with the rest of Etsuko's biological family, a massive loss that profoundly shapes her quiet, detached demeanor as an adult.