My Guardian Beast is the Demon Lord

Hedeya, this ordinary boy who even gave up on God, changed his style of painting after accidentally obtaining a Guardian Beast. As a commoner, he was admitted to the Academy of Magic and smoothly moved towards his dream-to become a magician.Everything seems to be peaceful and harmonious, but no one knows that a huge conspiracy to destroy the world is quietly happening.What, my guardian beast is actually a demon king?The devil king is amazing, you want to run away after eating my tofu?I just want to quietly be a rich and beautiful man, but God actually asked me to guard this world!