You gotta think strategically
You've got a great series, but it really seems that your background story is taking over your "main" storyline. With two characters going out each time, I suspect you'll need to merge the tribes soon, if Bahamut is to survive. At this point, you really can only vote out non-storyline people.
That said, if the winner of the contest is supposed to face Sephiroth, then I vote that Bub be the next one off the team. Bub has agility and bubbles, but he's really not going to be effective as a finalist.