Final Fantasy X begins late in the story, with the main character, Tidus, waiting with his allies outside the ruined city of Zanarkand. Tidus narrates the series of events leading up to his present situation, which spans most of the game's storyline. It begins in Tidus' home city, the unruined and high-tech Zanarkand, where he is a renowned star of the underwater sport blitzball. During a blitzball tournament, the city is attacked by an immense creature shrouded in water known as Sin. The city is destroyed, and Tidus and Auron are taken by Sin to the world of Spira.
After arriving in Spira, Tidus is rescued by Al Bhed divers in the area, and upon asking where he is from, one of them, Rikku, tells him that Zanarkand had been destroyed 1000 years earlier. After another attack by Sin, Tidus is separated from the divers and drifts to the tropical island of Besaid, where he meets Wakka, the captain of the local blitzball team. Wakka introduces Tidus to Yuna, a young summoner planning a pilgrimage to the ruins of Zanarkand to get the "Final Aeon", the only weapon capable of defeating Sin, who is described as mankind's punishment for their sins. Accompanying Yuna are her guardians, Lulu, Wakka, and Kimahri. The party travels to gather aeons, defending against attacks by Sin. The party encounters Auron, who joins them. He reveals to Tidus that Yuna's father, Lord Braska; Tidus's father, Jecht; and himself made the same pilgrimage and defeated Sin ten years ago. Tidus thought his father had died at sea ten years earlier. Following more encounters with Sin, they are joined by Rikku, who is revealed to be Yuna's cousin. Throughout the pilgrimage, Tidus and Yuna draw close through their shared experiences and mutual interest.
When the party arrives in the Guado city Guadosalam, Seymour proposes to Yuna, and she informs the group of her intent to marry him to give Spira hope. Seymour's aide, Tromell, guides the group to Macalania's temple, where they see a message from Seymour's late father. He declares he was killed by his son, and that Seymour's evil nature will destroy Spira. The group engages Seymour in battle and they kill him; soon afterward, Sin attacks the group and they lose track of Yuna. Rikku guides the group to the Al Bhed "Home", which is under attack by Yevonite soldiers. While searching Home's base, Tidus learns that a summoner must give their life to perform the "Final Summoning", leading to his desire to find a way to defeat Sin that would not result in Yuna's death. Using the Al Bhed's airship, they escape the base before it is destroyed. The group finds Yuna in Bevelle, where she is forced to marry the now unsent Seymour. They interrupt the wedding and escape with Yuna towards Mt. Gagazet, where Seymour has slaughtered the Ronso tribe; after defeating him again, the group heads to Zanarkand.
Tidus learns that he, Jecht, and the Zanarkand they hail from are summoned entities akin to aeons. Long ago, a summoner named Yevon had the city's surviving people become "fayth" so that he could use their memories of Zanarkand to create a new city in its image, removed from the warfare on the Spiran mainland. Sin was also created, given form by Yevon to serve as armor; protecting himself and the fayth. While continuously summoning Dream Zanarkand, Yevon lost his humanity and became known as Yu Yevon, a being existing solely to maintain Dream Zanarkand's existence. Sin's true purpose was not punishment for mankind's sins, but to prevent the discovery of Dream Zanarkand's existence by persistently attacking the people of Spira.
Once the player completes Yuna's pilgrimage, Lady Yunalesca—Yevon's daughter and the first summoner to have defeated Sin—tells the group that the Final Aeon is created from the spirit of one close to a summoner. After defeating Sin, Yu Yevon's spirit possesses the aeon, transforming it into a new Sin. The group decides against using the Final Aeon and they defeat Yunalesca. They then seek a new way to permanently destroy Sin that will not require any sacrifices. This leads the group to enter Sin's body and battle Seymour, Jecht's imprisoned spirit, and Yu Yevon. Sin's cycle of rebirth ends, and the spirits of Spira's fayth are freed from their imprisonment, dispersing the pyreflies of the aeons, Dream Zanarkand, and Tidus in the process. Afterward, in a speech to the citizens of Spira, Yuna resolves to help rebuild the world now that it is free of Sin. After the credits, there is a brief scene with Tidus underwater. He opens his eyes and begins swimming upward, and the screen fades to white. This scene segues into the sequel, Final Fantasy X-2, in which Yuna investigates Tidus' possible survival in order to continue their relationship.
