Tiararose Lapis Clementille, a noblewoman of the Kingdom of Lapis Lazuli, faces a crisis on the day of her graduation. Just as she is about to be publicly denounced by her fiancé, Crown Prince Hartknights, she suddenly recalls memories of a past life in modern Japan. She realizes she has been reincarnated as the villainess of an otome game she once adored, a story where her character is fated to be cast aside for the heroine. True to the game's events, Hartknights falsely accuses her of bullying, breaks their engagement, and declares the commoner-born mage Akari as his new bride. As Tiararose resigns herself to exile, the script is shattered by the unexpected arrival of Aquasteed Marineforest, the powerful and handsome crown prince of the neighboring maritime kingdom. Having secretly admired Tiararose for years, he publicly proposes to her on the spot, spiriting her away from her doom.

Tiararose is the reincarnated protagonist who, rather than being inherently wicked, was simply playing the role assigned to her by the original game's narrative. Possessing the knowledge of a dedicated otome game fan, she is intelligent and self-aware, yet often doubts her worth due to her predetermined "villainess" label. Her savior, Aquasteed Marineforest, is the prince of Marinforest and the hero of the game's hypothetical sequel. He is calm, calculating, and utterly devoted to Tiararose, having observed her true kind nature from afar. The initial antagonist, Hartknights Lapis-Lazuli Lactomuth, is the prince of Lapis Lazuli who blindly follows the game's plot, while Akari is the seemingly sweet heroine whose actions consistently paint Tiararose as a criminal.

The story begins in the opulent, magic-infused courts of Lapis Lazuli before shifting to the contrasting setting of Marinforest, a kingdom known for its powerful navy, water spirits, and more pragmatic political climate. The initial narrative arc focuses on the dramatic denunciation and Tiararose’s rescue, culminating in her engagement to Aquasteed. A second major arc follows Tiararose as she adapts to life in Marinforest and learns to trust in a love that was never part of the original game's scenario. Here, she must navigate the politics of a new court, build genuine relationships, and overcome lingering insecurities from her past life. A subsequent challenge arises from the magical creatures of Marinforest, as the kingdom's water fairies had hoped for a different bride for their prince, leading to supernatural trials that test Tiararose's resolve. Throughout these events, she uses her knowledge of the original game to avoid pitfalls, but finds that her new path with Aquasteed creates an entirely original story free from a predetermined script.