Princess Loutier of the Kingdom of Florella, known as Lou, is called the Flower Princess because she possesses a magical power that causes flowers to bloom when she sings. This ability is inherited among Florella's royals, but hers is exceptionally strong, and she has been warned since childhood never to use it after accidentally harming someone years ago. Despite having little understanding of love, she is happy when Prince Raynaud of an allied kingdom proposes marriage. On the day of their wedding, however, the Olgan Empire, a hostile nation, launches a sudden invasion. To protect her homeland, Lou agrees to go alone as a hostage to the enemy empire. There she is forced into marriage with the fourth prince of Olga, Julius, a masked man whose face she has never seen.

Initially, Lou resents her imprisonment and her unwanted marriage, hoping only to return to Florella. Yet as she spends time with Julius, she begins to notice a gentle and sacrificial side to him. He acts to protect both his country and her, and his devotion gradually softens her animosity. Caught between lingering hatred and budding affection, Lou finds herself drawn to him despite her intentions. Her emotional turmoil deepens when she becomes entangled in a political incident within the empire. Ultimately, she must confront her own feelings and decide between vengeance and love. The story follows her journey from reluctant captive to someone who learns the true meaning of her own heart, culminating in a choice that will define her future.