This is stating the obvious to some, but I'm surprised how many folks go, "Oh, that makes her so much less of a slutty goth."
Lulu. Miss Grouchy.
Best danged guardian after Auron... and both of them miserable failures in their own minds, ironically enough.
Why?
When Lulu and Wakka couldn't dissuade Yuna from starting summoner's training, Wakka shrugged and went back to his blitzball, and Lulu went on a pilgrimage. No, two. She's been on more pilgrimages than Auron, and for all we know, more than any guardian in Spira, since it's a risky business (4 summoners succeeded in a thousand years? Doesn't bode well for their sidekicks).
There can only be two reasons for Lulu's sudden choice of guardian as a career, despite her apparently rather hot and heavy relationship with a blitzer named Chappu...
~ To get to Sin first and save Yuna the trouble.
~ To gain experience enough to be able to protect Yuna when the time came.
Which comes in handy, since she serves as a walking tour guide for most of the game, and is better able to roll with the punches of Yevon's betrayal when the time comes.
However, Lulu's a little more worried than most of them about failure, due to her experiences with losing one summoner and having another bail out halfway through.
When I first started playing this game, I thought she was all about the T&A. It took me a while to notice the brains, the backbone, and the expertise.
I still don't get the dolls, though. I just don't.