YouTube - Kingdom Hearts Birth By Sleep Final Mix Secret Ending Aqua in the Realm of Darkness between BBS and KHI.
YouTube - Mickey Mouse & Ansem the Wise In between BBS and KHII, Mickey meets 'Xehanort'.
So, what my theory is that KH 0.5 might be the events of what happened between BBS to KHII? And, even though TAV (Terra, Aqua, Ventus) are gone. There is still a hero, Mickey. Mickey is doing his best to prevent the worlds from falling into darkness, but because of the events of the Heartless invasion of Radiant Gardens and Maleficent, he finds that he is unable to defeat it. And, he confronts Yen Sid about this and the retired Keyblade Master tells him that he needs to find a boy that weilds a Keyblade and that will be the only way that the darkness can be stopped and the worlds return to their place. Just a theory though.
YouTube - Mickey Mouse & Ansem the Wise In between BBS and KHII, Mickey meets 'Xehanort'.
So, what my theory is that KH 0.5 might be the events of what happened between BBS to KHII? And, even though TAV (Terra, Aqua, Ventus) are gone. There is still a hero, Mickey. Mickey is doing his best to prevent the worlds from falling into darkness, but because of the events of the Heartless invasion of Radiant Gardens and Maleficent, he finds that he is unable to defeat it. And, he confronts Yen Sid about this and the retired Keyblade Master tells him that he needs to find a boy that weilds a Keyblade and that will be the only way that the darkness can be stopped and the worlds return to their place. Just a theory though.