Mirabelle, a daughter of a branch family of the Count Amerun, ends up attending social gatherings as a "substitute" at the request of her cousin Anabelle, who looks exactly like her. While bewildered, she was enjoying the social scene as a pastime until one day, Anabelle made a shocking request: "I’ll give you the 'Ailes' jewelry. In exchange, I want you to be my 'substitute' as his fiancée and make him fall head over heels for you." The partner is the cool Duke Dewarie, nicknamed the "Blizzard Excellency"! Having had her greetings ignored by him, Anabelle proposed that after making him fall in love, she would break off the engagement. Mirabelle, a huge fan of "Ailes," accidentally agrees, but…!? A romantic comedy between a slightly clumsy count’s daughter and a beautiful, ice-attribute duke begins!