I believe he'd be Odin.
Why?
Seymour is a man obsessed with death. He has hands drenched in blood: he has already killed many people just for standing in his way, such as his father (thus avenging himself for his abandonment and usurping his position to the boot), Maester Kinoc (so he wouldn't stand in his way forcing him to kill Yuna, which he was unwilling to do), most of the Ronso (for standing on his way whilst he pursued Yuna) and he still wanted to bring just about everyone else in this. Odin's Zantetsuken can slice just about anything, bringing instant death to his target. I believe this incarnation of Odin wouldn't use a scimitar, but a spear (Gungnir), like FFIX's one as he appeared on the FMV destroying Cleyra.
But, UltimaGriever, Seymour didn't have the bond the FA requires to be strong enough!Who said he didn't? Yuna hated him alright, because of his disregard for human life and that he killed his father, but the reciprocal is not true. Seymour
did in fact love her, it is stated by the Ultimania Omega guide that he did, and there are numerous hints through the game that he did. If he really couldn't care any less about her, he'd let the Sinspawn Gui kill her, instead he
frickin' held the monster's paws together and pinned it down with his sheer strength so it wouldn't devour her. He would always
stand by her side and I'd say he sure as hell liked that kiss, because it seemed like he was eating her face surely you jest. Everytime he appeared he'd be
really polite to her
whilst being quite rude at Tidus, because he was everything that Seymour was not: he was young and cheery, while Seymour was older and gloomy and, last but definitely not least, Yuna
had chosen Tidus, not him. This made Seymour and Tidus resent each other as if they were the crap stuck to the crap stuck to the bottom of their shoes out of jealousy. So yes, there was a Tidus-Yuna-Seymour love triangle in FFX. :p
And Seymour was so
attached to Yuna that he was willing to kill her in order to have her only for himself (perhaps, if he did kill her, he'd go to the Farplane on his own, without needing to be sent there?) and,
at the time of his death and right before he was sent,
he had looked inside her eyes... He looked
grateful that she was the one who sent him at last, because the only reason why he just didn't crush everyone's guts until then was because of her. He wanted to have her either way, and, if only she had picked
him instead of Tidus, he would be able to be her FA, because of his strong feelings for her.
But, what about the horse and the spear?!?!!!!!!Seymour has horse tattoos on his chest. The horse could be Sleipnir, on whom he'd mount and carry a spear loosely based on his staff and crush Sin asunder. I wish I had enough skill to draw what Seymour-Odin would look like in fayth statue and aeon form, but I'll try.
But, UltimaGriever, Tidus and Yuna are the OTP!!!!!!!!! NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
I still believe in Seymour/Yuna against all odds! DDDDD: