Moribito: Guardian of the Spirit.

Balsa the spearwoman is a wandering warrior, who takes on the task of saving lives, in atonement for a past sin. On her journey, she happens to save a prince, and is tasked with becoming his bodyguard. And he is going to need one, for his own father, the emperor, wants him dead. Throughout the story, Balsa's past will come to light and they will uncover mysteries about Chagum's condition while developing a family-like relationship with each other and others.