Haikara-san ga Tooru takes place during the 1920s and follows the story of Benio, a high-spirited tomboy, and her relationship with a charming soldier named Shinobu, who has a mixed German heritage. Benio is a determined and independent person who values freedom, athleticism, and socializing. When she meets Shinobu, she dislikes him despite his help in rescuing her from public embarrassment. However, Benio is shocked to learn that her family has arranged her marriage to Shinobu. The plot takes numerous unexpected turns that include Shinobu's involvement in the war, Benio's inner conflict about commitment, and her adjustment to new family and work environments. Moreover, the threat of the Kanto earthquake adds to the tension.