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! General Rahn of the Kai Empire engineers a devastating flood that sweeps Hak and the precious herbs away! With the Thunder Beast nowhere to be found, an anxious Yona nevertheless intends to join the Four Dragons on the battlefield as the Kohka army summons all the tribes for war!