Princess Yona lives an ideal life as the only princess of her kingdom. Doted on by her father, the king, and protected by her faithful guard Hak, she cherishes the time spent with the man she loves, Su-won. But everything changes on her 16th birthday when tragedy strikes her family!

Yona's travels take her to the Water Tribe's territory, which is said to be the most beautiful area in the Kingdom of Kohka. But despite this region's reputation, a drug known as "nadai" has spread throughout the land. When one of Yona's friends becomes affected by nadai, how far will Yona go to help him?