Barn is a bright and cheerful boy, but lost his memory two years ago, apparently to hide an important or painful past memory. He was found unconscious in the Karukia mountains, and was found by Blood, a half-man, half-white tiger, who took care of him. In order to try to help Barn regain his memory, Blood and Barn leave the Karukia mountains to the kingdom of Melbird, where there is a rumor that a fortune-teller lives there that may be able to tell Barn about his past.
The fortune-teller speaks of a legend of the "Star Sea" that has been told in the kingdom of Melbird since ancient times, of a hero that will open the "door" of the "Rig Veda" to save the world, and says that Barn is the person who has come to do this, and that by doing so, he will regain his memory. He then disappears before Barn and Blood without another word.
Without anywhere else to go, Barn and Blood set out on the venture of the Star Sea legend, to travel over the seas to foreign lands to regain elemental treasures and go against the Guardians that protect them, and for Barn to regain his hidden memory: a memory that will save the world.