In the Kingdom of Acacia, royalty are born with blonde hair, silver hair, blue eyes, etc. Everyone is born gorgeous and good-looking. The third princess, Caroline, who was born with chestnut hair and ink-blue eyes in such a beautiful kingdom, has lived her whole life in a detached palace because her family hates her as a “plain princess”. Her sister used her as an outlet for her stress, and her family forced her to work every day. One day, she receives a summons from her father and rushes to the audience chamber, where she finds Leinhard, the crown prince of Tuscany, a kingdom inhabited by beastmen. He also has snow-white ears and a tail, and suddenly asks her to marry him, claiming that they are “mates of destiny.