Sunset Shimmer and Pinkie Pie are romantically involved, and Pinkie introduces Sunset to her fetishes, which Sunset really gets into as well. And Sunset adds some fetishes of her own.

Chapter 1 contains cake sitting/sploshing, soap/washing, and buttplay
Chapter 2 contains olfactophilia, farts, buttplay (spanking, butt rubbing, and facesitting), foot fetish, tickling, and a BIT of omorashi/wetting
Chapter 3 contains olfactophilia, pet play, omorashi/wetting, farts, mud, and soap/washing
Chapter 4 contains bondage, omorashi/wetting/golden showers, farts, and buttplay
Chapter 5 contains farts, omorashi/wetting, and buttplay

As usual, don't expect too high quality, though I have been trying to improve and follow advice on how to do so. Not recommended for anyone who doesn't like the stories I've written before. Situations will be stretchy as usual so don't take too seriously. And this time I'll try not to let any harsh words convince me to stop.