OK. Way I see it, Tsukasa's a girl.. In a lot of the pics, we see a kid, and (even though it's very tough to see normally) the kid's either wearing short shorts or a skirt.. I go with skirt. This is a wild guess, but I think he may be a picked up orphan as well. You see her at that big apartment/boarding house-like building, then that smiley family comes up, as if they're seeing if he's good child material... He got adopted by a family, who I don't think had any other children. His mom died when he was young, and his father took it rather hard and eased himself in the form of alcoholism.. A few years later, Tsukasa came into "The World" and spent most of his time in the game, because of his rather unpleasant home life. He fought a lot, gaining experience.. (He's a good fighter, even though you barely get to see, Mimiru once said he's "very experienced") Then he entered that dungeon, found that chest, got that tablet thing.. Met Maha, heard that voice.. Entered Aura's world. I think that voice is not really his mother (I mean, that would be creepy if a dead person was talking to you in a video game..) but maybe that "broken man"'s loved one.. Well, not really her, just a memory, some AI, like the broken man. Aura may be their daughter, if they ever had one, or what the old guy imagined what his daughter would look like... (She reminds me like the girl in "The Ring".. Everyone will suffer. :D ) Now.. Tsukasa likes to believe that the voice is his mother because he's looking for some comfort in his loneliness..
This is just one crummy theory... I haven't seen the entire series yet... I'm a newbie so I don't know if there's one solidified theory in this forum.. I just wanted to share that. ^_^