A mysterious spear-wielding woman named Balsa arrives in the New Yogo Kingdom. After saving Prince Chagum from a thinly veiled assassination attempt, ordered by his own father, Balsa is tasked to protect him from his father.

Balsa (Haruka Ayase) is a 30-year-old female bodyguard-for-hire. Her life changes when she saves Imperial Prince Chagum who is being carried away by a raging river. They then attempt to return the great egg of the water spirit, which is in Prince Chagum's possession to its source in the sea. Along the way, they are hunted by hired assassins.—AsianWiki