Magic Knight Rayearth Volume 4 is the fourth volume in the Magic Knight Rayearth manga series and the first book in season 2.
The second Magic Knight Rayearth story arc opens up with the Magic Knights feeling depressed over killing Princess Emeraude, their familes notice this and are naturally worried. The three girls then return to Tokyo tower and begin to recall the world of Cephiro and their wish to return when suddenly a bright light transports them back. They appear before a crumbling world looking nothing like the Cephiro they once knew, they enter a strange castle and meet their friends once again. Clef explains that since the Pillar disappeared, the world has started to crumble leaving Cephiro open to invasion from other countries and that if they don't replace the pillar then the world will soon disappear. He also informs them that Cephiro was protected by a barrier before but it disappeared when Princess Emurade died allowing roads to other countries to open up.
The Magic Knights ask to help out and are given back their weapons and armor with slight changes, Clef explains that they won't evolve like before but will change shape when it reacts to the users hearts. The Magic Knights head out and encounter an air battleship from Autozam where they fight it's leader Eagle when suddenly the battle is interrupted by a strange man bearing a striking resemblance to Zagato. It turns out that he is Zagato's brother Lantis and that he recently returned to Cephiro from Autozam when the pillar fell. The girls then talk to their potential love interests meanwhile two other countries Fahren and Chizeta are closing in on the castle. Clef explains that anyone can become the pillar and that the one has to be strong of heart and pass a test but they don't know what or where it is. The volume ends with Lantis having a flashback stating that the tragedy which caused the Pillar to fall must never be repeated and that he will end the legend of the Magic Knights.