Tasuku Nakamura, who was thrown into the sea in a marine accident and tried to help his best friend, ended his short life of 25 years. Formerly a mediocre office worker, when he opened his eyes, he was in the form of a six-year-old baron's daughter, Sophie Linier. At first she was confused by the changes, but she was reincarnated as a beautiful girl and decided to live as a lady in a different world. The struggle of a 6-year-old girl with the soul of a 25-year-old boy begins ... !! *Note: The following chapters were split into two parts in the original serialization and later combined in the volume releases: 1, 3 to 5, 7 to 15, 18 to 23, 25, and 27 to 32.*

Mireille, the princess of the small kingdom of Grilles, is an old maid when she suddenly receives a marriage proposal from King Cain of the great kingdom of Drake. It soon becomes clear that the woman he fell in love with at first sight is her younger sister, and that he has mistaken her for someone else. However, by order of her father, the king, she is forced to marry him in her sister's place. Mireille was prepared to bear the burden of her deception, but for some reason, she continues to be treated with care as a bride—!? (Source: Overlap, translated)

Mireille, the princess of the small and struggling nation of Glires, suddenly finds herself the subject of a marriage proposal from Cain, the king of the great nation of Drake. However, it quickly becomes clear that Cain's true object of affection is her younger sister, and the proposal was made to the wrong person. Despite this revelation, Mireille is forced by her father to take her sister's place and marry Cain as a stand-in bride. Prepared to bear the guilt of this deception, Mireille braces herself for a cold and loveless life. Yet, to her surprise, Cain cherishes her deeply as his bride. Why does he continue to treasure her so sincerely despite the truth? Source: OVERLAP