Twilight gets a letter from Celestia, telling her to try out a duplication spell. It's a really tough spell, but she believes Twilight's able to do it. And then they have sex, and it's hot.

I was inspired by the cover art of the fic. ^^
http://electronvolt.deviantart.com/art/Dirty-Mind-291433545

ATTENTION: This is partially a TwiDash fic(Though, not entirely.)