Final Fantasy X
Voice Actor: Alex Fernandez
Seymour is initially unveiled in Luca before the Blitzball tournament. It is revealed that he is the son of the now deceased Jyscal Guado and that he has become Maester Seymour Guado in his father's sted. Seymour announces that he wishes to continue his father's work and that he is proud to be a Maester of Yevon.
Shortly afterwards, he is called into action when Luca is attacked by fiends. He shows off some of his impressive powers as he calls the Summon Anima to assist him.
I Will Take Full Responsibility
When Yuna arrives at the Mushroom Rock, her progress is impeded due to an operation involving the Crusaders and the Al Bhed. Seymour gives them safe passage and says he will deal with any problems which arise as a result. When Wakka questions the operation, Seymour simply suggests he should forget he saw anything.
As the operation progresses, the mainland is attacked by some sinspawn and Seymour joins Yuna and Auron to try and defeat it. Following their success, he tells Yuna not to try and fight Sin yet as he powers are still too weak.
Actors Must Play Their Parts
Upon reaching Guadosalam, Seymour decides to entertain them at his home. Here he shows them a projection of how Zanarkand used to look 1,000 years ago before the time of Sin. He also takes the time to ask Yuna to marry him, but when Auron questions his motives he merely replies by saying "Actors Must Play Their Parts".
Leaving Yuna with things to ponder, Seymour leaves for Macalania Temple, which is where he is confronted by Yuna about the things he has done in the past. She knows that he killed his father and has come to stop him before he can do any more damage.
Justification For A Warped Mind
Seymour openly admits that he murdered his father, as he had been plotting his demise for many years prior its actual execution. When he was just a child, Seymour and his mother were banished to the Temple of Baaj by his father as the Guado people would not accept their presence in Guadosalam.
Seymour's mother loved Jyscal, and this made Seymour resent his father even more, especially when she took her own life. Gradually the bitterness took over his mind and he began to plot the demise of his father and hatch his overall plan.
Would You Pity Me Now?
After realising that Yuna knows that he killed Jyscal, Seymour realises that his only option is to take their lives and cover the whole thing up. Unfortunately, he underestimated Yuna and he is defeated. However, before Yuna can send him, Tromell appears and rescues him.
Seymour thinks he has the last laugh as he kidnaps Yuna and takes her to Bevelle, where she is forced to undertake a marriage ceremony with him. Part way through the ceremony Yuna tries to send him, but he threatens her friends and she desists.
I Killed Jyscal, Hadn't You Heard?
Following Yuna's defiance, she is tried as a traitor of Yevon in a trial run by the four Maesters. During the trial, Yuna reveals that Seymour killed Jyscal, something which Kelk Ronso didn't know. Mika decides that Yuna cannot be allowed to live, but Seymour asks that he be allowed to kill her should she manage to escape.
Kinoc goes with Seymour to the exit of the Via Purifico, but Seymour kills him after a short period of time claiming that he "put him out of his misery". He then uses Kinoc's body to help morph himself into Seymour Natus, who is defeated at the combined efforts of Yuna and her party.
Once I Become Sin, Your Father Will Be Freed
Not one to be detered, Seymour again confronts Yuna at the summit of Mt. Gagazet. Yuna attempts to send him again, but Seymour informs them that he has slain all of the Ronso on the mountain. He also reveals that he plans to become Sin so that he can end the Spiral of Death that Spira is caught in.
Despite being defeated as both Seymour Natus and Seymour Flux, Seymour returns once again inside Sin as Seymour Omnis to make his final stand. He is defeated and this time Yuna is able to send him, ending Seymour's existance within Spira's physical realm.
Final Fantasy X-2
Voice Actor: Alex Fernandez
Seymour appears very briefly in a flashback involving Baralai which takes place shortly before Yuna's initial visit to Guadosalam in Final Fantasy X. Baralai is asking for protection from Bevelle due to his actions with the Crimson Squad.
He also appears in Final Fantasy X-2 International + Last Mission as a boss character and as a bonus character who is obtainable using Creature Capture. He can join the party upon completion of the Farplane Cup.