Seirei no Moribito

Once every 100 years, a Water Fairy implants an egg into a person who then becomes the Guardian of Fairies. This time, the responsibility falls on Chagum, the second prince of the New Yogo Kingdom.

Chagum's life isn't easy. The king finds Chagum an inconvenience and attempts to have him killed. As a result, the queen asks a female guard, Balsa, to protect Chagum. In addition to this, beings from another world, known as Nayugu, constantly attack him in order to eat the egg carried in Chagumu's body.

(Source: MU)