I think that Rikku dresses like that because she is a thief.When you're a thief you have to be able to move quickly and not distracted be your clothing.I also feel like Square could have made Rikku more modest clothing-wise.I mean Yuna and Paine can run and jump and stuff.Rikku isn't a slut,she just dresses like what we would consider to be slutty.She's also an Al-bhed,people known for there eccentric clothing,or lack thereof.She doesn't act like a slut at all.She has the personality of a kid!I think that if Rikku was real and she was with a guy he would feel like a pedophile,I mean she is just so childish!She's still one of my fave characters though,despite her clothes.