Shortly before arriving, Tidus learns that he, Jecht, and the Zanarkand they hail from are summoned entities akin to aeons based on the original Zanarkand and its people. Long ago, the original Zanarkand battled Bevelle in a machina war, in which the former was defeated. Zanarkand’s survivors became “fayth” so that they could use their memories of Zanarkand to create a new city in their image, removed from the reality of Spira. Once they reach Zanarkand, Yunalesca—the first summoner to defeat Sin and unsent ever since—tells the group that the Final Aeon is created from the fayth of one close to the summoner. After defeating Sin, the Final Aeon kills the summoner and transforms into a new Sin, which has caused its cycle of rebirth to continue. The group decides against using the Final Aeon, due to the futile sacrifices it carries and the fact that Sin would still be reborn. Yunalesca tries to kill Tidus’ group, but she is defeated and vanishes, ending hope of ever attaining the Final Aeon.
— Wikipedia on Final Fantasy X
2022.02.04 Friday ACHK