Funny thing, my group's running a One Piece campaign, but we're using the Mutants and Masterminds 3E rules. I'm currently at work, so I can't check the d20 system you're using, but I can say this: you should be able to do anything that's even loosly related to your element/substance. Remember, this is based off an anime and since when has an anime kept 100% to how things work in reality?