Heisuke Sugita is a 39-year-old factory worker for an auto-parts maker in Tokyo. He has built a modest but happy life for himself with his wife Naoko, 36, and their daughter Monami, 11. In March 1985, Naoko takes Monami with her when she returns to her parents' home in the mountains of Nagano to attend a memorial service for one of their relatives. The ski bus they are riding on the way there drives over a cliff and crashes. Naoko is pronounced dead shortly after arriving at the hospital, but Monami miraculously pulls through after being given little chance of survival due to the brain damage she has suffered. The consciousness that returns to Monami's body, however, is not her own but Naoko's. Heisuke and Naoko decide to keep this to themselves, and to live as if Naoko is indeed Monami.
All seems to be well at first as life resumes with just the two of them, but then gradually they begin to grow apart. Given this chance to start life over as Monami, Naoko decides to become a doctor and actively begins preparing herself. But as Naoko (in Monami's body) moves toward building an independent life for herself, Heisuke, who still thinks of her as his wife, finds himself helpless to do anything about the confusion and anger he feels over the changes she is experiencing. The rift between them continues to widen. Then, when Monami (Naoko at heart) falls in love in the tenth grade, making the rift virtually irreparable, Monami's consciousness suddenly reawakens. For a time, the girl's consciousness switches back and forth between Naoko and Monami, but gradually, the Monami periods grow longer, and Naoko's consciousness fades away after filling Monami in on what happened during the five years before she reawakened.
Time goes by, and Monami gets married at 25. On her wedding day, Heisuke is astonished to discover that Naoko's consciousness still resides within Monami. Immediately after the bus accident, when she decided to go on living as Monami, Naoko had put her wedding ring away in a secure location. No one but she and Heisuke ever knew the secret place, but it now comes out that Monami knows where it is.
Exploring the relationships between husband and wife and parent and child following a family tragedy, this work catapulted the author into the top ranks of Japanese writers. It was made into both a movie and a television series, and has been translated into several languages. An English translation has appeared under the title Naoko.