The story starts in 1983. Instead of attending the opening festivities of the 17th store, Oshin Tanokura decides to go on a train trip. Her family is in a frenzy, not knowing where she disappeared to. Oshin's grandson, Kei, remembers the story of the kokeshi doll she once told him. Based on a hunch thinking about the story, he goes on a trip of his own and finds Oshin. From there, the two of them begin a journey back in time, traveling through various parts of Japan including where she once lived years earlier, and starts remembering the difficult times that she faced in her life.
In 1907, seven-year-old Oshin is sent off by her father to work as a babysitter to support her family. Her boss was a timber trader, and despite the physical and verbal abuse from the chief servant at his household, Oshin insisted on enduring it for the sake of her family. A sympathetic local teacher persuades the trader to allow Oshin to attend elementary school. However, Oshin's classmates bully her and threaten to harm her ward. Oshin reluctantly stops going to school. However, when she is unjustly accused of stealing money, she runs away, and for days suffers through blizzards as she walks back home to be with her mother, nearly freezing to death.
Oshin is rescued by a man named Shunsaku, a Japanese Imperial Army soldier-turned-deserter, and a self-described "hunter". She stays with him during the long winter until the snow melts. She furthers her reading and writing skills under Shunsaku. When the blizzard subsides, they are found by an army unit, and Shunsaku is shot dead. Oshin is then escorted by the soldiers to a hut and interrogated about Shunsaku. A senior soldier then comes into the hut and tells Oshin that the unit will escort her home. However, Oshin declines the offer, mentioning that she knows the way, and walks home on her own.
Upon her return, Oshin is once again sent out to work as a babysitter, this time to Kaga-ya in Sakata. Things do not start well because of Oshin's association with the deserter, Shunsaku. She also clashes with Kayo, the family's eldest daughter and designated heir; they are the same age as her. But the matriarch and owner of Kaga-ya, Mrs. Yashiro, views Oshin as a role model to make Kayo more sensible less like a spoilt child. Kayo resents this but they eventually become good friends. Mrs. Yashiro sees the potential in Oshin and personally traines her in reading, writing and arithmetic using the abacus. Kayo's mother is unhappy with the attention Oshin receives, feeling that it is socially out of place for a servant. However, she accepts Oshin into the family when Oshin saves Kayo from a falling electricity pole.
Oshin stays at Kaga-ya for eight years until she turns 16. During this time, she is loved by everyone, including her co-workers. In the interim, Oshin's beloved grandmother dies and the kind Mrs. Yashiro sends Oshin back home in time to spend the last moments with her dying grandmother. Her death steeles Oshin's resolve to make something out of her life and to no longer be poor.
One day, a mysterious man, Kota Takakura, visits Sakata. While Oshin is looking for Kayo, who was at the beach, Kota uses Oshin as a foil, as his girlfriend, to elude the police. Kayo and Oshin's lives are changed by this man, the son of a wealthy landowner and an idealist, who is a strong follower of socialism and wants to better the lives of the indebted sharecroppers through political agitation and land reforms. Kota reveals to Oshin his political mobilization efforts and wins her over with his idealism and passion. Unfortunately, both Kayo and Oshin fall in love with Kota, and while Kota does not reciprocate Kayo's love, feeling that it is simply an infatuation as he feels something special with Oshin. In the meantime, Mrs. Yashiro trains Oshin in the tea ceremony and other feminine arts to boost her chances of marrying well. She attempts to set Oshin up with the second son of a wealthy Sakata family. But the match falls through because of Oshin's secret love for Kota. Kayo, who has grown up to be passionate about painting and literature, has no interest to take over Kaga-ya, nor in the feminine arts to improve her marriage prospects. She believes in marrying the man she loves. A rebellious Kayo leaves home on the day she was supposed to meet her prospective husband, fleeing to Tokyo with a reluctant Kota. Heartbroken and feeling troubled by Kayo's decision to run away from home, and unable to reveal the truth to the Kaga family about Kota, a guilt-stricken Oshin decides to leave Kaga-ya and return home.
Upon returning, Oshin is re-united with her older sister, Haru, who was sent home from the textile mill where she had contracted tuberculosis. Haru's last wish is to see her secret love, her former supervisor, Hirano, who is persuaded to visit her. While visiting, Hirano reveals the poor working conditions at the textile mill and his failure to improve the workers' welfare for fear of losing his job. In the meantime, Oshin discovers that her father wants her to work as a barmaid to supplement the family's income. Haru warns Oshin that the agent touting the job had previously conned her fellow textile workers into prostitution. Haru persuades Oshin to run off to Tokyo, giving her a name and address in Tokyo and some money. Haru dies at the age of 19 in 1916. Oshin's mother, who had also returned home to take care of Haru, supports Oshin in her decision to go to Tokyo. Following her sister's death, Oshin runs off to Tokyo to follow Haru's dream of becoming a hair stylist.
Oshin trains under Madam Taka Hasegawa in traditional Japanese hairstyling. Two years into the apprenticeship, Oshin receives a letter from her mother informing her of the sudden death of Sayo, the younger sister of Kayo, from pneumonia. Oshin had also been her babysitter at Kaga-ya in Sakata. Oshin takes leave to visit the grieving family in Sakata. She's told that Kayo had not returned home and was somewhere in Tokyo. Kayo's mother pleads with her to stay behind but Oshin is unable to do so. Oshin is still hurting emotionally from the time Kayo and Kota left Sakata two years earlier. A year later, Oshin bumps into Kayo at a coffee house in the Ginza district while visiting prospective clients on a house call. Kayo had been working as a waitress at an upscale Ginza coffee house. Due to his agitation work, Kota was not usually around. Upon learning about Sayo's death, Kayo decides to visit her family in Sakata, staying there for a month.
In the meantime, Mrs. Yashiro arranges Kayo's marriage with the third son of an Osaka rice dealer, Masao, a graduate of the Tokyo Imperial University (present-day University of Tokyo), who is prepared to marry into the family to help the family business succeed. Kayo wants to leave for Tokyo to be present for Kota's return. But Mrs. Yashiro collapses from a heart attack, so Kayo reluctantly stays behind. She telephones Oshin to inform her when Kota returns to Tokyo. Oshin meets Kota when visiting Kayo's rented room to clean it. He tells Oshin not to let Kayo know that he is back in Tokyo and tells Oshin that he doesn't love Kayo, and that he had only used her to fill the emotional void left behind when he wasn't able to be with Oshin. Oshin leaves for Sakata to attend Kayo's wedding. She does not update Kayo with news about Kota, and regrets not doing so for the rest of her life. (Oshin will learn much later that Kayo was in an unhappy marriage with Masao.) Through Kayo, Oshin meets Ryuzo Tanokura, a rich textile trader who frequents the Ginza coffee house. The third son of a prominent Saga family, Ryuzo decided to leave home for Tokyo to strike out on his own. Seven years Oshin's senior, Ryuzo falls in love with her, and the two get married. However, they go bankrupt due to the depression and the incorrect trading methods Ryuzo had implemented. Their first child, a boy, is named Yu. With great effort, they manage to start over again.
While they survive the Great Earthquake of 1923, their house and business are destroyed, forcing them to return to her in-law's house. Since their marriage was not approved by Ryuzo's mother, Kiyo, Oshin suffers greatly while living with them. She is seriously injured while attempting to escape the family, and her infant is stillborn due to the hard labor she has to endure while working in the fields. She finally takes Yu from her in-laws, with the help of her sister-in-law Tsuneko, and attempts to rebuild her life. Later, she finds that she can no longer be a hair stylist due to her temporarily-paralyzed right hand.
She owns and operates a small bar-restaurant, works as a pastry chef, and even a peddler of fresh fish. Finally, with her husband's help, her fish store business in Ise thrives, and Oshin establishes a small but bustling raw seafood shop. The story continues until 1983, following Oshin's adult life as she becomes a wife again, raises more children of her own, and experiences real-life events, including more earthquakes and World War II.