Based on a fantasy novel by Uehashi Naoko & Futatsugi Saki.
Once every 100 years, a Water Spirit implants an egg into a person who then becomes the Guardian of the Spirit. This time, the responsibility falls on Chagum, the second prince of the New Yogo Kingdom.
Chagum's father, the Emperor, believes this spirit is the reincarnation of a demon defeated by his ancestor, the first Emperor, and secretly orders his son killed. Chagum's mother, the Second Empress, fearing for her child's safety convinces a female bodyguard for hire, Balsa, to protect Chagum. Balsa accepts fully knowing that this assignment may be her last, but she does so to atone for sins of her past.