Following her defeat and cleansing of Nightmare Moon, Princess Luna is still feeling a little off from the experience. With some time alone, she does what she can to settle her urges. This also happens to be when Princess Celestia walks in on her sister. Somewhat shocked at the sight, the alicorn sisters have a brief conversation and eventually come to an agreement. They'll both help each other out.
This is a Sequel to Fellatio is Magic.
Contains: Futa, Incest, Deepthroat, Cock and Ball Worship, Facefucking, and Rimming.

Commission for Donttouchmysqueenus.
Derpibooru: 2386325