Necron?

[The Crystal]

I think it wouldn't have felt right if they just had let it end with Trance Kuja and it wouldn't feel right either if Kuja transformed again. So I was kinda glad Necron appeared (though I was spoiled, I knew he would appear).

It's not just that "it wouldn't have felt right", but that "it wouln't make any sense". Before the fight against Super Trance Kuja, he said that the process of assimilation between Gaia and Terra already started, and he couldn't do anything to stop it, even if he tried. Meaning that killing him would NOT stop the process. It didn't depend of him anymore, but the tree itself(that was causing the assimilation).
This is why we fight Necron. To kill the tree and save Gaia.

And seriously... Necron's theme is a remix of the Iifa Tree's theme, the tree dies after you kill him, he change between the colors(blue and red) of the two planets the tree is connected with, etc.
Stating that Necron don't have any connection with the tree, is simply ridiculous.

I just interpreted NeoExDeath as another form of ExDeath, now with a slightly less poorly thought out cliché name than before.

His original name is Exodus.