Good. It's thought-out, that much is clear, however gives the story a number of plot holes. 1. Xehanort tried to kill-off Sven, they're not on good terms, let alone where they would work in cahoots. 2. When Zexion was defeated the shard of Vanitas was freed from the bonds of Ienzo's vessel. Vanienzo (Ienzo Vanitas) slaid Xemnas and XH, not to help him, but as an act to show he was no longer his slave or puppet. 2. (Going by what F_H told me and my understanding of it) Vanitas possessed Riku vessel to try and take Kairi out of the picture, but feeling the shard in her own reacting to Riku's, Kairi's pure heart kicked both shards out of their vessels, but at the cost of making Ukrix and Namine (Which made the two weaker, in some regards). 3. Demyx was sent, along with Xulan back to the organization for some sort or recon. 4. Ienzo is back at the base, which does not reside in RG. 5. It be MX in Terra's vessel that would kidnap Kairi (Let's try not to confuse the readers ^_^). 5. If Vanitas needed another heart and not his original one, then why would Ventus need to? Sora has become Ventus' darkness as Ventus has become Sora's Light.
When the feel it best they're going to seek out their respective half (Being either Ienzo, Riku, or Kairi). However, two of them are really messed. The Riku half is sadistic in both regards, and up until the point he meets Riku he's been doing dispicable things to innocent lives. The Kairi half is a masocist in both regards, while she loves any male deeply connected to Sora, Vanitas, and Ventus she hates those who are female in this regard and has the urge to kill them for her sick, twisted, selfish desires.
Aside from the flaws mentioned, I kinda like the idea of LExi and Riku fighting, though I'm none too sure why :/ A.R.A.V. fighting Braig also sounds interesting, though to patch-up the holes maybe it (The reason the go there) could be to apprhend Braig? I let you stew that over. Another idea I wanted to pitch was Xehanort steps out of the machine (That made him a heartless) only to find Sven waiting there to strike him down (Braig can be there for kicks if you want, or to indicate he hasn't been found by ARAV yet ^_^). Anyways, during the struggle a girl let's Xehanort get away, only so she can strike a deal with Sven as she claims she can help and she wants revenge on Xehanort (Guess who the girl is ;D. How's it all sound?