Originally a much larger line, the busts were limited to Aki and Gray.  Aki appears slightly demure with the Coronet headgear, and Gray (apparently) comes in two designs, the only difference being one wears the the half-helmet and the other wears the Nightmare.  I don't have either of these, so I can't really comment on anything more than appearance, but I do know there were an awful lot of prototypes auctioned off a year or so ago on eBay.