I want to say I still think this is a bad idea. Note that in my problems with this I haven't read the fanfiction.com stuff.
a) Having the new enemy come and attributing everything that has happened previously is a weak plot twist unless done really well, however as all you have at the moment is that idea it is weak.
b) Having the enemy doing something like stealing pyreflies has little meaning, they steal the dead? I guess the most similar thing to this is FFIX where they kill with the Angel of Death and use the Lifa Tree to take the planet. But having the plot be some random aliens who were btw not connected to at all in two games having a sinister plot of stealing something that has little value doesn't work. The plot seems trivial.
c) No major enemy, a group of aliens doesn't cause the kind of caring about an enemy that a truly great one gets ("the audience hates a good villian but loves a great one"), you give no sense of an enemy that actually has any depth to them.
d) It seems like you just want characters you like to come back, but honestly using the farplane to have them come back doesn't work, especially with Auron. The reason he never went to the farplane before the end of X is he had something important, a promise to his best friends, the people he cared most about. And he fulfilled that promise. He succeeded. This story is planning to throw what his a lot of his character is about for the sake of reusing someone you liked? I'm sorry but that destroys who Auron was.
e) Just triviality occurs a lot, you take away trema's character (not saying he had much of one, but this kills that) to connect it with your plot, he suddenly becomes a breeder for gladiator fights in other worlds...w...t...f...
f) Once I actually (if I ever do) read your fanfic I'll probably have many more criticisms. But a game lacing a remotely interesting enemy that actively disrespects and destroys what was important in the prequels is not my idea of a good continuation. Keep in mind I'm a skeptical bastard and I dislike a lot of fanfics, but this has serious problems.
