Quote Originally Posted by Khisanth
Exhibit I) In Scan 4 from the foreign language expose on the front page:
(http://www.eyesonff.com/images/news/ffxiiiscan4.jpg),
at the top right is an inset table listing the number of characters allowed in a party since the first FF. For example, in FFI, four characters are allowed, while in FFXI, six characters may fight simultaneously. I believe the authors of this article then are commenting on the likliehood of FFXIII's heroine going at it alone throughout the game!
Link is broken, so I can't say anything about this.

Exhibit II) On the same scan, and many of the others displaying battle scenes, the "radar" box at the top left of every scan shows the heroine's position in relation to her enemies. If there were ever to be more than one character in the party, where would their position be displayed? Unless they occupied the same exact space, it would make the radar box somewhat difficult to comprehend. Also, the heroine's position always remains in the center of the box in every shot, again supporting the fact that she may be your only playable character.
The radar may not be centered on her, or may be centered on her only when it is just her in the party. The radar may zoom out when more than one playable character is in the party so that it has the ability to display all of their positions.

Exhibit III) The heroine's mastery of many different weapons may be another clue. Traditionally, each character had their weapon, be it sword, spear or staff; those weapons may change in appearance, but characters rarely traded in one genre of weapon for another. Yet, here we have a heroine that in the few glimpses we have wields both sword and firearm, with perhaps more options forthcoming. Granted, the gunblade has appeared before, but not in this capacity (Squall and Seifer utilized the gunblade, but I can't recall them ever taking shots with it). While my FF knowledge is not all-encompassing, I cannot recall a major playable character with the ability to switch their weapon type. Therefore, it may be that our heroine will be the only character available, with her ability to change weapons making up for the lack of other characters.
Earlier FFs had the characters use many different weapons. Job systems aside, FFVI had many different types of weapons the characters could utilize. While some used specific weapons (ie. Relm uses brushes), Lock could use daggers (and some swords I think) as well as full moons and other weapons along those lines.