Ok, so you killed the Morph Demon in the Old Metrolian Castle? I can't remember if the Earth Demon is available only after that point, or some time before it. The Morph Demon is the last part of the main storyline. You can only give the Muura Gem to one of the two guilds, and the Mage Guild is the right choice. Did you recruit Scott and Alessandra before Metrolia's destruction? How about Van Helsing after that incident? If you have 22 characters in your Dream Book roster, then you have them all!
How many spaces do you still have left in the Noticeable Victories and Prestigious Victories section in the Dream Book? There is only one entry that I've never been able to find, the one in the top-right corner of Noticeable Victories! The one above Mazurine and to the right of Yen Karis. If you have all but that one, then you've completed most of the game, and you might only need to beat the Single-Character Tournament in the Coliseum with several characters to get the rewards if you haven't already.