i think after the video terra goes to finish master zehanort but cant and fuses with him and then they both lose their memory and become ansems apprentice , but when zehanort splits into heartless and nobody xemnas recognises roxas and allows him to join organisation 13 for 2 reasons (1.we want to find out more about the keyblade as he was able to weild it ) (2. the terra side of him recognises him roxas but as Venn instead of him being roxas)
but this is only and idea . i have no clue if this anywhere near true
