According to Gematsu, Sword Art Online: Lost Song will be adding player-versus-player multiplayer as well as a new character.

The livestream that was hosted earlier today mentioned that it will also be adding more "large-scale" quests, a new boss, a new character (which is assumed to be Lux) and they will be taking user feedback as well. Sword Art Online: Lost Song will release on the PlayStation 3 and Vita in Japan this week on March 26th.