This story is a clopfic. This clopfic is seduction porn, and focuses heavily on anal. I use the Romance tag lightly.

Rarity is in heat again, and she's bored of using her own hooves.
As good a time as any to seduce her closest friend and use her to make herself a quivering, sticky mess.

The cover image is a cropped version of a NSFW image created by artist wickedsilly, and was not used with permission.