 When "X" is removed from Xemnas and the letters are rearranged, you  get the name "Ansem." Applying this to Roxas and Xehanort gives  "Sora" and "no heart," respectively. This is applied to all members  of Organization XIII, as their names are their real names rearranged  and an X added, however only the original names of Ansem the Wises  6 apprentices (Xemnas, Xigbar (Braig), Xaldin (Dilan), Vexen (Even),  Lexaeus (Aeleus) and Zexion (Ienzo)) are given in the game.