Magical Insulator: the Knight King of Ember Fortress

On the magic test day, Luo Cheng's crystal didn't light up. The instructor announced that he had zero talent, his fiancée broke off the engagement in public, and his classmates threw humiliating fireballs. The fireball disappeared before him. He didn't know what that meant. He was exiled to the Ashen Fortress in the northernmost reaches of the Empire - a ruin forgotten off the map of the Frontier. There was an alcoholic and decadent knight, a disabled dwarf veteran, a demoted and indifferent female knight, and a boy who couldn't even lift a sword. Luo Cheng didn't know that this fortress contained the empire's biggest secret. And in his body, the most taboo blood in the empire was flowing.