Ryuukyuu Timeline: Mirai Shoujo to Inishie no Ou  

Ryukyu Timeline: The Girl from Future and the Ancient King, 琉球タイムライン -未来少女と古の王-

A historical fantasy that unfolds a mysterious story between a high-school girl from Urasoe and Satto, the king of the Ryukyu Kingdom.(Source: AniDB)