I was thinking... What if something happened durng the battle at the Keyblade Graveyard, that sends Terra, Ventus and Aqua to the future? Set during the events of Kingdom Hearts or Kingdom Hearts II, The BbS Keyblade trio, must help Sora, Donald and Goofy, and to find a way back to their original timeline... I would have tried this on my own, but I'm too busy to do so.