The Final Aeon (究極召喚, Kyūkyoku Shōkan?, lit. The Ultimate Summon) is the aeon a summoner gains at the end of their pilgrimage to Zanarkand. The aeon is seemingly intended to be used only once: during the final battle with Sin, in a ritual called the Final Summoning.
The Final Aeon is created from someone who shares a deep relationship with the summoner: a friend, family member, or lover. Lady Yunalesca was the first to call the Final Aeon, her husband: Lord Zaon. If the Final Aeon has enough power to pierce Sin's armor Yu Yevon, an unsent spirit, who resides inside Sin's "shell" takes control of it. The summoner is killed due to the bond between the aeon and summoner being severed when Yu Yevon possesses the aeon. Yu Yevon uses the aeon to rebuild Sin, and this period of rebirth is known as the Calm.
When Seymour Guado was young his mother brought him to Zanarkand and had Yunalesca turn her into a fayth for Seymour to obtain the Final Aeon, but Seymour never used the aeon he'd obtained to battle Sin.
Obtaining the Final Aeon is initially Yuna's goal, but after she learns of the futility of defeating Sin with the Final Summoning, she rejects it and decides they must find another way. They pacify Sin via the "Hymn of the Fayth" and fly into it with their airship and traverse Sin's innards till they reach the core. In the final battle before challenging Yu Yevon, the party fights Braska's Final Aeon, Jecht, the last fayth Yu Yevon used to create Sin.
Known Final Aeons and their FaythEdit
Final Aeon is Jecht's EX Mode. As Final Aeon he gains the Regen status, which slowly regenerates HP. Jecht also gains the ability "Full Combo", letting him continue his Bravery combos even if the initial strike misses. This lets him overwhelm opponents with powerful combo attacks, and also makes it easier to strike when pausing to charge up his attacks.
Final Aeon reappears as Jecht's EX Mode.