You ever see the movie The Entity? It's from 1983 and it stars Barbara Hershey. It's about this girl from a strict religious upbringing who is constantly fucked by a predatory, horny ghost. I doubt it was Casper, although this spirit was also very friendly. That film is notable for the amazing full frontal nudity from Hershey (and her body double) as her tits are squeezed and legs spread eagle at one point by the invisible fucker. It's also great jerk off material because it's all the fucking with some guy's hairy ass and balls in the way. And from a practical standpoint, there's no need for condoms or contraceptives when you're fucking a ghost. It's the ultimate version of safe sex.
Eva Green's character on Penny Dreadful, Vanessa Ives, had her own invisible screw session over the weekend. She's completely naked on the bed as she's possesed and boned. We see her always not bashful, big tits but none of her ass and vag unfortunately. Her nakedness was still hot enough to make the woman who walked in on her supernatural boning faint. Eva's body has been known to have that effect on guys so it's not surprising women feel the same way.