Create Ghibli-style clouds with flat planes and clever shaders.
When talking about big puffy clouds in 3D volumetric effects might come to mind. However, you may want to reconsider creating simulations and volumetrics in Blender if you’re going to mimic those painterly clouds in Anime.
Puffy and Painterly Clouds.
A pair of tutorials on the subject cover some alternate methods for getting that Ghibli-style cloud look. The first by Lightning Boy Studio (David Forest) shows why volumetrics may not be the correct answer. The tutorial covers creating clouds using replicated planes, normal maps, and some clever shader tricks to get a result that looks very much volumetric. Forest once had a look at creating painterly trees in Blender using another technique.
The other tutorial from Kristof Dedene offers a different approach, opting to create the clouds by using a procedural shading network. You can even download the shader here.