Yuna was born in Bevelle to a Yevonite father and an Al Bhed mother. Her mother was killed in an incident involving Sin shortly after her birth, however. When Yuna was around the age of seven her father, Braska, resolved to become a Summoner to stop anyone else from suffering the lose of a loved one as he had. He enlisted an exiled warrior-monk named Auron and Jecht; a man who suddenly appeared in Spira and claimed to come from a city that no longer existed, as his Guardians. Braska began his pilgrimage to the temples of Spira to obtain the Final Aeon. While on the island of Besaid he asked Auron to take Yuna to Besaid so she may have a peaceful childhood. However, when the pilgrimage ended and Jecht and Braska sacrificed themselves to defeat Sin, Auron was mortally wounded by Yunalesca. Crawling down Mt. Gagazet, he makes it as far as the outskirts of Bevelle before he dies. Before dying, he places his mission to protect Yuna upon a Ronso named Kimahri Ronso.
Kimahri travels to Bevelle, where he meets Yuna and takes her to Besaid. Even though Kimahri initially attempted to leave afterwards, Yuna pleaded with him to stay and he complied. At Besaid, she becomes close friends with Lulu and Wakka - the two seeing her as a younger sister. Eventually, she too decides to become a Summoner like her father, and refuses to allow Lulu and Wakka to change her mind. She, Lulu and Kimahri travel through the Besaid Cloister of Trials where she begins praying to the Fayth to commence her role as a Summoner and obtain the Aeon Valefor. When she leaves the temple as a Summoner, she encounters Wakka and a young man named Tidus in the room alongside Lulu and Kimahri.
She begins her pilgrimage to Kilika with Wakka, Lulu, Kimahri and Tidus as her Guardians. Due to her previous encounters with Jecht, Tidus' father, she was the only person who believed at the beginning that Tidus came from Zanarkand. At the ruins of Kilika, she performed her first Sending and obtains the Aeon Ifrit. The group then leaves for Luca. At Luca, Yuna hears a rumor that her father's guardian, Auron, had survived and was wandering the city. She began a search with Kimahri and Tidus just before the opening Blitzball match, however Kimahri ends up in a fight with two other Ronso and Yuna herself ends up kidnapped by Al Bhed in the hopes of making the Blitzball Besaid Aurochs lose to them. However, Tidus, Kimahri and Lulu manage to rescue Yuna, while the Besaid Aurochs win their first match in 10 years. Auron becomes Yuna's guardian the group continues their pilgrimage. While traveling towards the Djose Temple, Yuna is caught up in Operation Mi'ihen, where she first meets Maester Seymour Guado and witnesses the failure of the operation against Sin. Upon reaching Djose Temple she meets another Summoner, Isaaru, and receives the Aeon Ixion. On the Moonflow, she is yet again kidnapped by the Al Bhed. Rescued this time by Tidus and Wakka her kidnapper, Rikku, opts to join the pilgrimage in an effort to keep her from harm. At Guadosalam Seymour, having headed off the group, proposes to Yuna, and she decides to visit the Farplane before making her decision. Upon the group's return from the Farplane, it is discovered that Seymour had left for Macalania Temple, and so the group proceeds to follow himUpon crossing the Thunder Plains on the way to Macalania, Yuna observes the contents of a Sphere left to her by Seymour's father in the Farplane and discovers that Seymour killed his own father in order to become Maester. She decides to play at marriage in order to get Seymour to talk. This backfires when her Guardians intervene and they end up killing Seymour and being chased out of the temple by the now-bloodthirsty Guado, out to kill the ones who murdered their leader. Yuna and the group escape, only to be trapped under the ice. After being saved by Sin under Jecht's influence, most of the party, except Yuna, are taken to Bikanel Island and Rikku leads them to the Al Bhed's Home. However the Guado are in the midst of an attack on the Al Bhed base. In an attempt to escape and locate Yuna, the Guardians board an airship and escape. Yuna, having been left behind by Sin, was captured by the Guado and forced to marry Seymour, who is now an Unsent. She would, however, use this opportunity to play at marriage just for a chance to Send him once and for all, as it is a Summoner's duty to lead the dead to where they belong. When her Guardians show up in an attempt to rescue her from the forced marriage she is stopped by Mika, who threatened to force the Warrior Monks to kill her friends if she continues on with the Sending. She finishes the marriage ceremony to save her friends but, when Seymour decides to have Tidus, Auron, Kimahri, Wakka, Lulu, and Rikku killed anyway, Yuna threatens to commit suicide by jumping off the church unless he frees them; when Seymour tells her that the idea was foolish, she proceeds to jump, saving herself by summoning the winged Valefor. She then escapes to Bevelle's Chamber of the Fayth, where she receives Bahamut. However, her Guardians once again follow her, the group is caught, and she is tried for murder and treason. She manages to escape her execution into Macalania Woods with her Guardians Her faith in Yevon shaken, Yuna goes off to the spring to be alone with Kimahri in tow. Tidus goes after her, a mutual agreement between himself and the others, and, now knowing the truth behind the Final Summoning, apologizes for his eagerness to defeat Sin and filling her with hopes that they would be able to see his Zanarkand, believing that he had only stressed her out by doing so. However, Yuna assures him that he had in fact made her happy. Tidus attempts to convince her to quit her pilgrimage and stay with him, even toying with the idea of taking the whole group to his own Zanarkand. While Yuna considers it at first, her sense of duty to the rest of Spira was too great, and she resolved to go on; at that moment, Yuna, overwhelmed by the recent occurrences, lets down her emotional walls and breaks down crying. Tidus comforts her, and they kiss and share a moonlit tryst in the spring, with Tidus assuring her that he would always remain by her side no matter what.
On the slopes of Mt. Gagazet, Braska had left a video Sphere for Yuna, letting her know that whatever path she chose for her life, wether it be to duty or to herself, he would be proud.
Yuna and her Guardians then travel to Zanarkand, where she defies what the other summoners had done before her and refuses to sacrifice one of her Guardians to be the Final Aeon, forcing her to kill Yunalesca in self defence. Intrigued by Yunalesca's cryptic parting words, Yuna seeks out Grand Maester Mika in order to find out the truth behind Sin. Having learned the truth of Sin's rebirth, the group then hatch a plan to engage Sin head-on and venture inside to defeat the being at its core, the Unsent Summoner Yu Yevon. Yuna used all the Aeons she had obtained and managed to defeat Sin once and for all, becoming the High Summoner of the Eternal Calm. However, the destruction of Sin and Yu Yevon meant the fall of the Fayth and the death of Tidus, who was a product of the Dream Zanarkand created by Yu Yevon. During a tearful farewell Yuna tells Tidus that she loved him and after embracing Yuna, he jumps off the deck of the airship, disappearing into the Farplane. Though deeply saddened by Tidus' absence, Yuna informs the rest of Spira that she will stay strong aid in the reconstruction of Spira now that Sin was no more. Reminding them to not forget the people they have lost, or the dreams that have vanished