The roster is just a reference point for other players and even staff. Here is where staff will post your join topic for everyone to see, however, no one will be able to edit it. The Roster can be useful for seeing what someone's character is all about. The topic will just be moved to here and renamed as your character's name (unless it was that to begin with). These will be edited if you choose to switch character but your original one will still be here. If you are to switch then the name of the topic will be changed to your new one.
