Step family is actually aliens

[Strangebuddy]

Had a fun thought: what if we had the 18 year old kids (last year of high school) who suddenly end up with step-siblings their own age...but they're actually alien infiltrators?

Twins find out dad is getting remarried. This shocks them as he had only been dating his fiancé for a month. The ceremony happens just a week later (just a quick visit to the courthouse, and suddenly, the twins suddenly find themselves moving into a new house with a step-mom and her son and daughter, who are also apparently twins.

While the parents are off on a honeymoon, the kids start getting used to their new siblings. It's not easy though, as the siblings act...off. They always seem busy but can also drop anything their doing to spend time with the twins, they inflect words the wrong way, hold smiles or laugh a bit too long. Oh, and the twins find themselves instantly attracted to them. They try to hide it but they each get seduced when they're on their own and eventually even begin actively engaging in sex. However, the midst of their atypical practice, one of their step-siblings suffer an injury. The twins try to get them help but the other step sibling chloroforms them. One of the twins comes to early and notices a complex mechanical eye and a flesh like substance where the injury took place.

They sneak downstairs and see their step siblings, now in their inhuman bodies, making repairs to their disguises.

So now, the twins are trapped in a house with alien step-siblings who could be planning the destruction of earth, conducting research, or just very specific sexual tourists.

 

[sirhugs]

mmmm...tentacle sex.

you had me at the title.

 

[HandsInTheDark]

I wrote this once (not on Lit, and I ended up discarding it). It wasn't step-sisters, but a woman is found on the balcony of a guy's apartment, 30 floors up, and he has no idea how she got there but she's not dressed to handle the weather, so he invites her in. She turns out to be horny, etc and they eventually get down to it.

She's amazing - mind blowing sex every time, and she's fine with extra partners, rough play, anything he wants. He also realises he's falling under her thrall, but he cares less and less. Another orgasm, and then another...

In the end he's a hopeless sex addict and she's talked him into indiscriminate sex with other girls, and participating while she does other guys.

One day she's gone, leaving a message behind - "Hi. I'm an alien. We want this world, just not the humans on it. You've been contaminated by a pathogen that won't show up for thirty years. It's not detectable, onset is rapid and fatal, and there's no cure. You can't function without constant sex, so you'll be spreading it far and wide. You and the hundreds of other men I'll infect, because no one can resist me or my friends. We've got the shape and the pheromones and the skills that always get a Yes. For what it's worth you'll have a great thirty years, fucking everything that moves. It's all you ever wanted anyway."

The message vanishes. He goes to a hospital but there's nothing wrong with him than anyone can see, and in the end he ends up hooking up with a nurse...

I dumped it because it was stupid, but I think it could be made into something passable, so anyone who likes the idea can have it.