Tales of Civilian Knight Heroes

One day, a kind of monster named "Alien Beast" appeared in the world. Under the leadership of a "person" named "Alien Ancestor", it attacked the human world and occupied a large area of ​​human land. People can only huddle in cities with high walls. Fortunately, some people have awakened the "magic power". The King of Knights "Caesar" suddenly "disappeared" after a battle, and gradually disappeared from the eyes of the world as time went by. But in a certain city, a young man has shown his proud appearance on the knight's stage. What secrets are hidden behind this series of events?