Mixed Bathing in Another Dimension: Volume 5 by Nagaharu Hibihana

After learning from the Goddess of Water that Haruno and her party are in jeopardy, our hero Touya sets sail to an underwater city to save them. They finally reunite after a monstrous encounter along the way, only to be met with yet another shocking revelation. Meanwhile, Haruno hasn't forgotten the promise she made long ago—to take a bath together with everyone. Touya's Unlimited Bath can hardly be called just a bath anymore, but this time it'll be filled with more bare skin than ever before!