I originally thought Lulu (SPOILER) (she is too good for Wakka anyway, X2 got that wrong). But maybe Tidus is too immature for her. He could be her "toy boy" I suppose.

Rikku works much better, as she is closer to Tidus in age and bouncy personality.

Would have been great if the affection levels allowed you to decide. I wonder how you could redo the Macalania scene to fit it in. Maybe the designers figured too much alternative FMV would be needed.