[[OOC:S-sigh, my grammar late at night... Edit button, why you no exist?]]
Sounds good to me. Now let's see... you say "the ocean", but I'll assume it's the same as "water" - off the top of my head I can't think of a single culture that has water and the ocean as separate elements.
"Michiru" has a distinctly Japanese ring to it, but the Japanese have always been good at the whole 'not limiting yourself to one set of belief' thing, so there's no reason to jump to, say, Buddhism or Shintoism just because of that. And since you already mentioned Neptune and being a Pisces...
The question is, do I go for the obvious classical four, or do I include poor neglected aether in my guess?