I have a theory about why ven looks like roxas, I think that since whejn he was frozen in the secret ending for kingdom hearts 2 final mix, he was frozen for a long time. Later on, he was defrosted by the orginization and they took him. He forgot his name and so they called him roxas. (this is just a theory) and you know how on the island scene he closes with, his name was---- and you never hear him finish I think its ventus or ven. (again, just a theory) Aqua and Terra were most likely dead before roxas defrosted and the orginization found him. I have yet another theory of why master xehanort is different in kingdom hearts 2. I say that he time traveled after that whole battle scene and destroyed the past and he made himself younger and his old name was xehanort back then and thats why he doesnt like to be called xehanort! and he calls himself Xemnas!!!!!!! I think when he time traveled, he left Terra and Aqua left to die. I think I have a good theory and I think it might be true but its NOT TRUE FOR SURE!
Think about it, its possible.