A 28-year-old single woman named Kanai Yano is suddenly summoned to a fantasy world. There, she encounters a duke’s daughter named Rita Scryne, who is her exact double, and Rita’s father, Zack. They explain that Rita is meant to be a sacrificial pawn in a political marriage to the notoriously ruthless and feared King Eugene Astaroth, known as the Merciless Wolf. Desperate, they ask Kanai to take Rita’s place as the bride. With no way to return to her original world, Kanai has no choice but to agree to the arrangement.

The story’s central twist occurs when Kanai meets her intended husband. To her shock, the冷酷 (reikoku/cruel) king is none other than her first love from her own world, Hoshina Hiroto, who has somehow become the ruler of this strange land. This revelation transforms her situation from a terrifying obligation into a complicated and emotional reunion.

The narrative follows Kanai as she navigates the dangers and politics of the royal court while hiding her true identity as a substitute. Early arcs focus on her meeting with the King and the discovery of who he really is. Subsequent storylines introduce new challenges, such as a tense audience with the Queen Mother, who subjects Kanai to a difficult test, creating an in-law conflict in this fantasy setting. Later, the genuine duke’s daughter, Rita, re-emerges, infiltrating the castle by posing as a maid with hidden motives while the King is away on business, placing Kanai in a precarious position of having to face political schemes without her primary protector.