From Wikipedia:

The Guardian series (守り人シリーズ, Moribito shirīzu?) is a ten volume series of Japanese fantasy novels, written by Nahoko Uehashi. The first novel in the series, Guardian of the Spirit, has since been adapted into numerous media, including radio, manga and anime adaptations.

1. Seirei no Moribito (The Guardian of the Spirit): Adapted into the anime series. Balsa saves Prince Chagum of the New Yogo Empire, and is hired to protect him. He has a mysterious spirit living inside him, and his own father has sent assassins after him. Balsa has to protect him from the assassins and the dangers the spirit inside him brings. Published in English by Arthur A. Levine Books/Scholastic in the summer of 2008; translated by Cathy Hirano.

2. Yami no Moribito (The Guardian of Darkness): Balsa returns to the country where she was born to face her tragic past. But consequences of that past, and the secret that lies buried under the mountains, make her task a difficult one. Published in English by Arthur A. Levine Books/Scholastic in Spring 2009.

3. Yume no Moribito (Guardian of Dreams): People start becoming trapped in their dreams. Tanda's niece, Chagum, and the First Empress are all dreaming of a flower - a flower with ties to Torogai's past. Only a man with a supernatural singing voice can save them. English publication TBA.

4. Kokuu no Tabibito (Traveler of the Void): Chagum, who is now the crown prince of the New Yogo Empire, and Shuga are sent bearing greetings to a southern country, Sangal, for the new king's crowning ceremony. However, a black shadow is reaching towards Sangal. During his stay, the King-to-be of Sangal is fatally wounded. English Publication TBA.

5. Kami no Moribito - Raihou-hen (The Guardian of the Gods - The Visit): See below. English TBA.

6: Kami no Moribito - Kikan-hen (The Guardian of the Gods - The Return): When Balsa is in Lota, she meets two children, brother and sister, who are being sold away by a slave merchant. Balsa witnesses the girl killing the slave merchants when she became angry. But Asla herself does not believe that she did the killing. "God did it" she says, and will continue to seek "God's" help if people threaten her. Because of Asla's ability, the two are in grave danger. Shamans closely connected to the King himself see them as a threat towards Lota, and will either kill or use them as their weapon when there is a chance. Balsa and Tanda decide to act for the two. English TBA.

7. Souro no Tabibito (The Traveler of the Blue Road): English TBA.

8. Ten to Chi no Moribito - Lota Oukoku-hen (The Protector of Heaven and Earth - the Kingdom of Lota): English TBA.

9. Ten to Chi no Moribito - Kanbal Oukoku-hen (The Protector of Heaven and Earth - the Kingdom of Kanbal): English TBA.

10. Ten to Chi no Moribito - Shin Yogo Oukoku-hen (The Protector of Heaven and Earth - The Empire of Shin Yogo): English TBA (final novel)