This is the photoshopped version of Mogudan's Ayanami Rei Book 2. She's wearing bloomers and a gym shirt here, while *ahem* doing the less than 90 degree coital lambada.
comment #11430 lol, so that's where I saw this. I love Mogudan's work, Those books captures perfetly how Rei would act in a the hentai world... but it was a little sad