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!

A drug known as "nadai" has spread throughout the Water Tribe territory, so Yona and Riri, the daughter of the Water Tribe chief, are determined to end this drug crisis. However, their task is an uphill battle, and they couldn't have imagined the dangers that await them!