In Final Fantasy X Yuna is one of the main characters (only Tidus features more prominently than she does), and she is one of the chosen Summoners that has been given the task of going on a special pilgrimage, collecting various Aeons (basically mythical creatures that she can then summon to help her in battle) before sacrificing her life to cast the 'Final Summoning'. The reason she has been given this task is to bring peace to her homeland. For many years, and creature known as Sin has been terrorizing the world, and only by casting the Final Summoning can Sin be banquished – if only for a couple of decades. Final Fantasy X Yuna has completely accepted her fate that she must sacrifice herself for the greater good, when Tidus comes along and is adamant that there must be a better way. His motivations for this are partly selfish, as he has a love interest in Yuna, and does not want to see her die as he feels she is right for him.
One of the most interesting things about Final Fantasy X Yuna is that she was (possibly) the first ever video game character to have different colored eyes – one blue and one green. While this might not sound exciting, it was a big step in making video game and video game characters more life-like. The more realistic and believable a character is, the more we can relate to them and feel a connection towards them, and the more enjoyable and moving the game can be for us. This is true with all video games nowadays (especially RPG's, as they are very character and story-driven), and developers are always trying to make their characters as deep and as three-dimensional as possible.