Lady Tsukiko has been sickly and frail since childhood, treated as a failure by those around her. When her twin sister is supposed to marry Lieutenant General Kishi, a young man who rose through the ranks and is known as the Demon General for his ruthlessness, Tsukiko is sent as a substitute bride. She once met Kishi briefly, and his unexpected kindness became a cherished memory that supported her through difficult times. However, upon their marriage, Kishi bluntly informs her that once she fulfills her duty and bears him a male heir, he will divorce her without making a fuss. The story unfolds as Tsukiko navigates her new life in a tense, transactional marriage, struggling with her own self-worth and the cold demeanor of her husband, while hinting at the possibility that the arrangement might gradually give way to deeper emotions. Set in a historical military-aristocratic backdrop, this josei romance explores themes of duty, identity, and unexpected connection.