Yu Yevon Yu Yevon was the leader of ancient Zanarkand , Lady Yunalesca ' s father , and the creator of Sin in " Final Fantasy X " . Yu Yevon is represented by the letter A in the Yevon script alphabet . This symbol appears on his true body and in multiple places in Spira , sometimes paired with the letter Z , the symbol of Sin , symbolizing the beginning and the end of things . Profile . A mysterious entity , the only information given about Yu Yevon comes from Bahamut ' s fayth , Yunalesca , Maechen , and Grand Maester Mika . Yu Yevon ' s role is that of an impersonal antagonist ; while Jecht and Seymour fill the roles of personal antagonists for Tidus and Yuna , Yu Yevon has no personal connection with any of the main cast . Yu Yevon has no dialogue in his single appearance , so his personality is unknown . Accepting the doom of the original Zanarkand ' s he sets forth in creating and maintaining the dream Zanarkand ' s memory through the surviving citizens . In some respects , he can be considered a tragic character as he is incapable of stopping what he is doing . His appearance is a mystery as he is never shown in human form . Yu Yevon appears as a bizarre , floating creature with hooks and a glowing emblem of Yevon for a face . The nature of this form is unexplained . It may be that transplanting his soul from each Sin to its successor has diminished or destroyed his true physical form , leaving him in a parasitic , bug - like state . Yu Yevon also may have taken on this form intentionally , perhaps to facilitate his ability to possess aeons . Another possibility is this form is his appearance as a fiend ; this is unlikely though , as he retains the ability to summon Dream Zanarkand . He also appears shortly as a floating ball of light similar to a pyrefly to signify his ethereal form . Story . One thousand years ago Yu Yevon was the leader of Zanarkand and a powerful summoner . Zanarkand was at war with Bevelle , a strong military power that used mechanical technology to build weapons . Unwilling to let Zanarkand be destroyed , Yu Yevon had the surviving citizens turn themselves into fayth and used them to summon an idealized version of Zanarkand at the peak of its power . Yu Yevon gathered a horde of pyreflies and transformed them into an armor for himself , which became the creature , Sin . Yu Yevon gave the creature a set of simple instructions : destroy any machina or large settlement to stall technological evolution , and retaliate to all hostility with extreme prejudice . Sin ' s first act was to destroy the real Zanarkand and as the armies of Bevelle saw the destruction they retreated , bringing the first news of the great monster . Eventually , a religion was created around Yu Yevon ' s name , his worshipers not realizing they were praying to the one responsible for Spira ' s cycle of destruction . According to the fayth used to summon Dream Zanarkand , Yu Yevon is neither good nor evil . His existence only has one purpose : to maintain Dream Zanarkand while protected by his armor , which is why he is drawn to the Final Aeon when his former armor , Sin , has been destroyed . Shortly before creating Sin , Yu Yevon informed Yunalesca of his plan and gave her a means of calming the creature . Yunalesca passed the knowledge on to the leaders of Bevelle , thus beginning the teachings of Yevon . Every time a summoner destroys Sin , the aeon used for the Final Summoning is possessed by Yu Yevon and used to rebuild Sin . The period of time Yu Yevon is rebuilding his armor is known as the Calm . 1000 years later after being reborn many times over , Yuna and her guardians pierce Sin ' s armor and defeat Yu Yevon . This temporarily banishes Sin ( it later returns in " Final Fantasy X - Will - " , ending Yuna ' s - then Calm ) and allows the fayth to cease dreaming . Gameplay . Yu Yevon is the final boss of " Final Fantasy X " . He is accompanied by two Yu Pagoda s . He uses high level magic but the party is under constant Auto - Life effect provided by the fayth . Yu Yevon lacks magic that disables party ' s actions in a battle , like Petrify , to counter the Auto - Life . Every time Yu Yevon possesses one of Yuna ' s aeons they take on the appearance of the Dark Aeon s . This suggests that Braska ' s Final Aeon looked different before becoming Sin ' s core .