I have to admit FFVII was a really good game and the battle system shouldn't of changed to the one in XII.
I would make the main character an old man who has lost his memory and after a quarter of the game he dies but is born again as a child with painful memories who has to abide for his sins by travelling to heaven to be baptized by An angel but the main antagonist who is in fact the old man's twin when he is born again has sold his soul to the devil and has to kill the old man to prevent him from being purified so he will lay in hell.
Here's something I would like if you could play as the antagonist for a short while so the gamer could understand him like in almost all anime.