I'm curious when this scene is:
This is the picture that you can find all over the net, but I don't remember ever seeing it. There is also that part in the intro when Tsukasa's guardian "attacks" him and he dissolves. Is that just part of the intro?
I think they're clothes dissolved... to show them "Stripped" in two different ways: "Stripped" Mentally, and "Stripped" Physically. Notice how... ecstatic they all look when they're going through the tunnel and the clothes are dissolving, and etc? ... are these clothes, these forms, really "them?" Are they just shallow interpretations and dream forms of onesself, generated to please onesself because they're unhappy with their actual appearance?
and god said unto cain, "wow you're pretty stupid."
As far as my admittedly dodgy memory goes, that particular image was just on the promo stuff.
I'd assumed that the images of the game clothes & headsets dissolving was reflective of the act of logging out from The World, back to reality. But the characters expressions did puzzle me in that respect, so perhaps it is indeed more related to escaping the bounds of reality & playing what/who you'd really like to be in the game, instead? Tsukasa certainly initially regarded The World as a far preferable habitat to the crummy real world...
(and maybe this deserves its own topic, if there are other opinions on the dissolving clothes thing?)