Greham is the Jade Dragoon that fights for Imperial Sandora. He controls the Dragon Feyrbrand. He used to fight for Basil with Lavitz's father, Servi, but then turned because he wanted more power in order to equal the powerful Servi. Emperor Doel offered him the Jade Dragoon Spirit in exchange for his services, and he accepted, betraying Basil.
The strategy for Greham is fairly straightforward. Have Lavitz and Dart attack him with strong Additions and Rose or Shana use magical attacks. A Pellet helps a lot. Dragoon magic of Flameshot and Astral Drain will help as well.