After the male protagonist marries his wife, her older sister (sister-in-law) comes to live under the same roof with them for various reasons (such as temporary stay, overnight stay, or family gathering). The wife, due to her own physical condition (such as pregnancy, illness, or frigidity), is unable to satisfy her husband's strong sexual needs. To prevent her husband from having extramarital affairs or seeking other partners, the wife, in a state of extreme absurdity and inner conflict, half-jokingly and half-seriously suggests that he "solve" his sexual needs with his mature and attractive older sister (sister-in-law). With the wife's tacit approval and encouragement, the already ambiguous balance between the protagonist and his sister-in-law is broken, and the two cross the line of ethics and morality, embarking on a secret and passionate affair.
