Akatsuki no Yona

Since Yona is the only princess of a grand kingdom, she has been raised with great care by her doting father and protected by her childhood friend/guard Hak and others. However, her fate changes on her 16th birthday, when her beloved cousin Soo-won murders her father to claim the throne. She flees the castle to Hak's hometown and begins her new life.

(Source: Anime News Network)