Ok makes since in a way might as well, explain the whole zhuahir thing.

Once fifty thousand years ago a dragon hunter had fought zhuahir in a battle of the death. The ough the hunter knew he couldn't win against the dragon. He had sacrificed his life sealing it into his best friend which was also a member of David's family. 

Once the person that carries zhuahir dies he transfers to the next newborn. Fifty thousand years later David has zhuahir inside of him though the seal is slowly weakening that's why the academy doesn't want him to go anywhere they know if they can kill David before the seal breaks that's the end of zhuahir but also the end for the bane family blood line David is the last hell horse dragon and the last of his blood line.