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Interviewer: In the trailer, four characters are shown playing simultaneously. Is this possible in game?
Nomura: Multiplayer can be played with up to four people [or less if desired]. Not only that, multiplayer gives a sense of freedom, as this mode has no effect on the story. But it is possible to choose less then four, for the multiplayer content.
Interviewer: How does the multiplayer mode progress?
Nomura: The point is to basically complete given missions. For instance, defeating an enemy or whatever the goal of the mission is. There are various goals, both big and small. There is a constant feeling of competition in multiplayer, so sometimes the player may forget just what the goal is!
Interviewer: Is multiplayer mode possible for one player only?
Nomura: Multiplayer mode is rather complicated ; we had to design a growth (leveling) system. For example, when Axel is used in Multiplayer mode, Roxas will gain some extra experience from this as well. Also, you are able to customize your character freely. (He does not go into detail about the customization part, so it is unsure what).