Soredemo Sekai wa Utsukushii(2009)

The manga revolves around Nike, the determined princess of the Rain Dukedom who has a mysterious power: she can control rainfall. After losing a game of rock, paper, scissors to her older sisters, she is forced to unwillingly marry the king of the Sun Kingdom, Livius I. Livius (or "Livi" for short) conquered the world in three years, and is known as the "Dreadful King." However, when Nike meets him for the first time, she finds to her surprise that he is a boy younger than she is. Livius abruptly asks Nike to call forth the rain, and when she refuses, he has her thrown in jail. The story follows the two, who at first are a married couple only in name, as they gradually establish an emotional bond.

(Source: Anime News Network)