if I do published it, is there a way to get special permission from the creators of Final Fantasy X so that it wouldn,t be illegal. I know it weird, but is it possible?
As a writer, I can tell you from first-hand experience that getting ANYTHING published is VERY hard. There are agents and contracts and corporations involved in the novel business, and since you are dealing with something which isn't your own work but owned lock, stock, and barrel by Square Enix, you definately can't do this on your own without lawsuits getting involved.

The only way to get "permission" is the same way authors "novelize" movies and TV shows - through a long, draw-out process. Basically, since they own these characters and the storyline, you can only do with them what they allow you to, meaning - they most likely would buy the manuscript from you, and publish it themselves so that they have control over it. The chances of them being interested in this idea at all are slim, and the chances that they would hire some kid who has never published anything before to represent their game is even slimer.

Bottom line? DON'T worry about publishing yet. You're getting ahead of yourself. Write the thing first, and do it for yourself. For fun. When and if you actually complete the script, you can start writing letters and pestering company execs to think about your idea. It will probably get nowhere, but it doesn't hurt to ask. HOWEVER, enjoy writing it for the sake of writing it, because dreams of seeing it on a bookself most likely will never come true. Good luck.