Set in the 1920s, Haikara‑san ga Tooru follows the spirited tomboy Benio and her evolving relationship with the handsome half‑German soldier Shinobu. Benio is an outgoing, athletic girl who is determined to live life on her own terms. When she first encounters Shinobu, she immediately dislikes him, yet he repeatedly comes to her aid during a series of embarrassing mishaps. She is shocked to discover that she has been forced into an arranged marriage, and that her future husband is none other than Shinobu himself. The story then unfolds with a number of twists: Shinobu must go to war, Benio must wrestle with the prospect of marriage, and both must learn to coexist with her future in‑laws.