Here is my theory about Birth By Sleep Volume 2. In the secret ending of Birth By Sleep Final Mix, We saw Aqua fighting in the Realm of Darkness as well as scenes stretching through multiple games. My theory is that it will be a here/there kind of game. The game will be about Aqua in the Realm of Darkness and every now and then it will switch and show whats happening in the Realm of Light at this time. Since she's there up til after Kingdom Hearts II there is a good chance that this will be able to cover all the plotholes by making the game stretch out from Birth By Sleep to past Kingdom Hearts II