Guin Saga Vol. 1: The Leopard Mask (novel)

In a single day and night of fierce fighting, the arch-duchy of Mongaul has overrun its elegant neighbor, Parros. The lost priest kingdom's surviving royalty, the young twins Rinda and Remus, hide in a forest in the forbidding wild marches. There they are saved by a mysterious creature with a man's body and a leopard's head, who has just emerged from a deep sleep and remembers on his name: Guin.