Useless Cinderella's Feeble Attempt to Save the Kingdom

The Kingdom of Belveron flourishes with the power of water magic used by the Vilcast Family, earning it the title of "Land of Beautiful Waters." However, Lara, the daughter of the Vilcast family, unable to use water magic, lived being treated with disdain by her family as the shame of the household. One day, a proposal of marriage from the Kingdom of Tulumhut, which is struggling with water pollution, arrives at the Vilcast household. The Kingdom of Tulumhut arranged a political marriage, investing considerable wealth, to save their homeland using the power of water magic. The other party is the 38-year-old bachelor "Former Crown Prince who has fallen behind." However, the Vilcast family plans to force the useless Lara onto the marriage proposal, instead of her step-sister, Mary, who excels in water magic. Lara ends up marrying into the Kingdom of Tulumhut to save the nation as the "Goddess of Water." What awaits Lara, who cannot use water magic?