Akatsuki no Yona Yona of the Dawn
Currently, Hiryuu Palace has no one else next in line for the throne other than the fifteen year old princess, Yona, who had been raised with care. Finally, the night of her sixteenth birthday arrives. She expects it to be a wonderful day spent with her peace-loving father, Il, her servant and friend Hak, and her cousin Soo-won, who she had feelings for... However... That night, Yona goes to visit her father to tell him how she really feels, because he opposes to her getting married to Soo-won. However, when she gets to her room, she encounters a shocking truth.
[Source: Titania Scanlations]