Isn't "Yuna" Japanese for woman who work at men's bath houses and assist them with their, uh... needs? I guess that would make Yuna a little too nice to people.

No.

Yuna is the a Japanese name for a hibiscus flower. Specifically, it's a Okinawa ( the southern Japanese island) name. That's why she has flower motives in her costume. It's also one of the reasons why FFX has a island/water theme. Remember the 1st time Yuna walked on water & did a sending of all the island people who were killed by Sin? Those pink flowers in the water looked a lot like hibiscus flowers.

And I agree with robfinalfantasy that Yuna is a subtle, docile person. I also agree with the others that it's her upbringing & her culture. While the 'flash in the pants', flamboyant characters are good entertainment, it's usually the quiet, silent types who actually get things done.

Think of Yuna as an aikido specialist. Aikidoists avoid confrontation as far as possible. But when pushed, they'll twist & crack your bones. The flashy Kung-Fu guys are impressive but the aikidoists usually have a subtle aura of quiet power. Water is soft but it can also cause a lot of damage.