The character designs are done by Tetsuya Nomura, and are unique to say the least. But Nomura himself has said he has modeled some of the characters after past creations. That would explain why Yuna bares more than a passing resemblance to Rinoa and Tidus to Squall. We can only wait for more announcements from Squaresoft on the rest of the characters in the game to see who has been reincarnated.