Final Fantasy X originally wasn't going to be a Final Fantasy game at all, but a series called 'Seventeen.' The story revolved around a recent unknown disease that killed people on their seventeenth birthday. Yuna would have had the role of a doctor/nurse that went around giving the disease's cure to its inspected victims. It is eventually revealed that the 'cure' was in fact the source of the disease, and that it was established by the company that Yuna was working for to rule the world, by claiming that they were the only ones that could provide the cure in the first place. It is unknown what role Tidus and Auron would have had, if they were even thought out as characters in the first place. That being said, some of these concepts could have been made for Seventeen and not FFX