Doing this in a comment in case anyone else is interested.
Clouds:
-Blurred edge watercolor, both as a brush and as an eraser.
-Duplicated layer, covered with a crop-to-layer-below much darker color, combine the two, and then erase holes in the original layer. That all said, not totally sure if I can reproduce the effect.
-Fingertip blur to get the rain squall.
-High thin clouds are also thin thin thin fingertip blurs.
Background:
-Tone scraping for the sparkles in the water, then moveable blur set parallel to the horizon to give the impression of wave tops, then subtle use of mesh transform to distort the surface of the water to give the impression of big rollers.
-Progressively heavier blur the further away, screwed up and didn't jack up the horizon as much as it needs.
-Sand textures are crop-to-layer-below. Liberal use of blur and gradient there too.
Figures:
-Made both figures separately using my pinup template, a version of which you've seen. Also added additional layers for subtle line coloration and the bikini patterns.
-Both outfits courtesy of [redacted]. Hey, can't give away everything...
-Tona's tattoos were also separately created. However, they are not on full transparency and they have been blurred.
Did this in Manga Studio 5, a spectacular program. I know you've got it, Prof, but for anyone else out there remember that you get what you pay for... I'm a weak, weak amateur artist, but this software makes it happen for me. Glad people seem to enjoy the results!
Art By:
Chippewa Ghost