Gold Kingdom and Water Kingdom (2023) Anime Watch

Once upon a time, there were two rival kingdoms that did not get along. Every day, they argued over insignificant matters. When a dispute over removing dog waste ultimately turned into a war, God swiftly intervened and directed the two nation's leaders to exchange the most beautiful girl and the most intelligent young man for bride and bridegroom, respectively.

Saara, the princess of country A, meets the prince of country B, Naranbayar. As they pretend to be a married couple to protect the peace between the countries, they find themselves gradually falling in love.