Blue Dragon: Ral Grad

In Blue Dragon, shadows can fuse with their hosts. This is the history of the teenager, Ral, and his shadow, the Blue Dragon Grado, that his father, a king, imprisoned together in the dungeon of the castle when Ral was a young baby. One day, when the shadows besieges the castle, his personal educator, Mio, releases him to protect the castle and repel the shadows.

(Source: MU)