The main character is the realist hero who undertakes the task of rebuilding the kingdom. There are also likely to be nobles, commoners, and perhaps some antagonists who oppose his reforms.
The key character is, of course, the realist hero. He is the driving force behind the kingdom's rebuilding. Then there are the nobles. Some of them may support the hero's efforts while others might try to undermine him for their own self - interests. The common people are also important. Their well - being is what the hero is aiming to improve. And there could be some sort of antagonist, maybe a powerful noble or an external force that doesn't want to see the kingdom rebuilt in this new way.