The demo will be on a separate disc (ah ha! Blu-Ray has its limitations too ya know!!!!) The demo will be based on the opening to the game, naturally. Wouldn't be smart to spoilerize everything. Two other tidbits, I'll fess up and say I have no clue what these mean so I'll just quote verbatim: "One of the female characters, refered to as 'Pigtails Girl', has been through some tough times." And "Mr. 33CM's real name is based off of weather as well."

Source: FF-XIII.org