Why do the characters in Akatsuki no Yona have Korean names?
The setting for Akatsuki no Yona is loosely based on the Three Kingdoms of Korea period. The Kouka Kingdom is inspired by the Goguryeo Kingdom. Its neighbor Sei and Xing are based on Baekje and Silla respectively. You can also see that the three kingdoms are located in a peninsula in the manga and that they almost have the same layout as their real-life counterparts.