David needs to be the opposite of Charming. They are foils of each other who happen to be the same person. an example of it which is very clear is Snow and Angry Snow….we see the two in the same episode and it is very clear and distinct. They are still the same character and we see they have the potential for that extreme behavior. They way they act is not quite out of character but think of it as of your own character then take yourself into another time and then your brain becomes swiss cheese…you are still you but now with a different identity. That’s the best way to describe it without having ever experienced it myself.