Yuna is the main female protagonist of the game and is a fledgling summoner, who is setting out on a pilgrimage to defeat Sin. She has large shoes to fill, as her father, Braska, was the last summoner to defeat Sin.
Yuna is the only character in the game that is able to summon Aeons into battle. These Aeons take the place of your party members and can be quite powerful. Aeons can also be used as meatshields, summoned to take the more dangerous attacks instead of your characters. In addition to the Aeons, Yuna is basically the White Mage of the party, as she learns the majority of White Magic spells in her section of the Sphere Grid. She will gain a lot of magic, magic defense, evasion and agility, making her a strong party member to use in battles where magic will be featured.
Despite Yuna being a White Mage, all the cure spells in the game only affect a single target. Once you get access to Use and Al Bhed Potions, single target healing is really only used more for emergencies. In fact, Use is a much more versatile command than White Magic, especially when you combine it with Steal. Also, White Magic is not really effective for attacking enemies, since the only spell they get is Holy, which doesn’t come into play until much later in her section.
Yuna’s section of the Sphere Grid is loaded with Magic and Magic Defense. In fact, Yuna should have a higher Magic than Lulu because of her portion of the Sphere Grid. She also has pretty strong Evasion and Agility, but low Strength and Defense. Being the White Mage of the party, it’s only natural that Yuna has a large portion of the White Magic spells on her section, mostly consisting of buffs, the Cure tree of spells, and more. At the very end, she has Holy, which is about the only attack spell she will gain. Yuna’s section will run into Rikku’s section, but somehow getting Yuna onto Lulu’s portion is ideal, since her high magic is ideal for Black Magic spells.