1. Auron (Final Fantasy X)
Auron is quite possibly one of the most badass characters in video game history, and certainly in Final Fantasy's. In FFX, we are given a great deal of insight (through flashback-like sequences) into Auron's past and his reasons for journeying with Tidus and company. A prequel to FFX, then, makes perfect sense. The foundations of a story are already there: we know a lot about Auron, but there remains an air of mystery about him throughout the original game. Indeed, an in-depth exploration into his history with Jecht and Lord Braska, in a typical Final Fantasy JRPG, would be an intriguing prospect. With an evolved battle mechanic - though the 'count time battle' one worked well in FFX - and an intricately customisable sphere grid/crystarium-style system, the developers could focus solely on those three characters without the need for superfluous, peripheral party members. The original FFX was a huge success, though such a prequel would perhaps rely on the success of the HD rerelease regardless. Still, let's not get our hopes up, because it'll never happen. *sigh*.