For some reason, I've always loed the idea of forced alien sex, and possible pregnancy. Perhaps my character, a good girl, is driving home in some obscure contryside and gets beamed up by your character's spaceship. These aliens can look like anything your head desires, I'm not picky! Of course, this immediately leads to probing and 'testing' by the aliens to make sure that the female is good enough and has the right sexual stamina and strength to help carry on their race.
Of course, we can take this anywhere you'd like it to go. Please, pm me and let me know if you're interested!!