Hey guys, it sees as though part VII has now popped up thanks to TheWertle! For those confused about the other parts, don't worry all of it is neatly organized right Here.

VII - In KH, at the same time Sora became a heartless Roxas was born and entered the Organization. So if that's the case, at that point in time at Castle Oblivion Sora used a keyblade while at the same time Roxas would have been using a keyblade. Was this Sora's keyblade? Within the organization I think we particularly saw Roxas using a keyblade. And similar to Roxas, Sora served as another Keyblade Master conviently gathering hearts. So why was the Organization defeated?

The keyblade that Roxas used and the thing that Sora once lost in Castle Oblivion are the same thing. Furthermore, these two both used the keyblade at the same time. This can be explained by the relationship between Roxas and Sora. Thus, that both can wield two keyblades in fact has an important meaning. This is also related to Xehanort's memories, but this point can't be touched on just yet.

Furthermore, from the time that the two were both using the keyblade at the same time, the Organization itself was using Sora for their ultimate goal. Soon enough, each of the Organization's expectations differed. By changing Sora and Roxas's movements, eventually they became unable to use Sora for their true meaning. As a result, Sora became an obstacle to the movements of the organization itself and he had to be defeated. But even if Sora were to be defeated, you could say there are other things to think about in making that sacrifice.
Source: The Wertle