We originally thought the game was being developed by Triple A Games, but as Mai's appearance proves, there is no room in this game for that A. According to the rather jumbled press release that accompanied the trailer, the game will feature a tag system that allows players to swap characters in battle, with both player-versus-player and player-versus-environment game play abounding. The release also explained what we are seeing in this clip:
This movie presents the game play in very simplified version of 1)boss scene, 2)Public Park, 3)auditorium, 4)Venezia, and 5)class room stages, currently being developed, for purpose of showing the core game contents.
Well that certainly cleared that up, right?