Nemureru Mori no Rega

To save Princess Lorana from a sleeping curse cast by an evil dragon, Rega, captain of the kingdom's knights, faces down a wicked wyrm within an ancient forest. Drawing upon his devotion to the princess, who rescued him from a life of slavery many years ago, Rega slays the monster, freeing the princess from her sleep. But the moment she awakens, the girl begins casting wicked magic, slaying Rega's fellow knights and cursing the land, creating a "sleeping forest" which corrupts familiar figures into dark, monstrous forms. Stunned at this horrific sight, Rega looks up to see a crooked, crescent-moon smile in the night sky. Could this be the mastermind behind the corruption? And were those tears Rega saw in the princess's eyes as she gleefully destroyed the kingdom she called home?

(Source: Kodansha USA)