Rikku can upgrade weapons to do interesting things, like inflict poison with a hit or add fire/lightning damage. She can also upgrade armor to protect against those things. There's actually a detailed, complicated list of the various things she can add, and I'm willing to play around with other ideas, as well, since it's usually her taking items that can cause those effects and burning them into the weapon/armor. She loves playing around with upgrades, so if you need a weapon with a kick to it, lemme know.