Nishikaze to Taiyou

Nishikaze to Taiyou is a one-shot manga by Hiro Mashima. This one-shot was released in Shounen Rival on April 3rd 2010.

Summary
During a montage of moments of Zephyr and Sol traveling with their new companion, Raina, one of the panels is of them watching her Skinny Dipping while she is Showering under a Waterfall.