Yuna isn't the main character of FFX. And even so, Seymour isn't very successful at playing mind games with her once she finds Jyscal's Sphere.
And Tidus doesn't really treat Seymour any differently than most heroes treat their villains. He hates Seymour, that's about it.
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"I couldn't stand a day without a past or future. I need to live each moment to keep fighting here and now."