Read manga: Blue Dragon: Ral Grad

manga
Summary:

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”.