Ever since losing his virginity to his older sister Sakiko, the younger brother has never been able to forget her body, even after getting married. Sakiko, who had long resisted his feelings, finds herself tormented by dissatisfaction in her marriage and can no longer suppress her own desires. One day, she makes the choice to give in to him. Thus begins an illicit affair between the now-grown siblings within the family household. This deep, emotional story explores how their forbidden relationship unfolds.