The Blue Blaze (Revised and Retold)

After his father left, Ethan had a hard time defending himself in school. He was always the weakest and pushed around a lot; thankfully, he had his friend Keith to help him out when he needed it. During a confrontation with his high school bullies, he transforms into a dragon and massacres them in rage. He escapes into the dragon realm with his friend and finds out about his father's past and discovers an enemy devoted to wiping out the dragons.