Step-sibling joins incestous coupling

Pretty simple idea: step-sibling accidentally spies siblings having sex (twins or older siblings who are in for a visit) and winds up joining in.

There's a number of ways it could happen of course. Could be spontaneous where they are either pulled (literally) into it or worn their way into it, or could be a more prolonged story where they hide what they found and then get brought into an ongoing incestous relationship.

For example: step-brother arrives home from school and finds his college age sisters at home eating each other out.

Spontaneous: oldest sister catches him and after swearing him to secrecy, decides to get some leverage by having him have sex with her and her sister and taking a few pics. Besides, she and sis could always use an on-call cock.

Prolonged: step-bro seemingly gets away but is confronted by one or both sisters. They let him know that they've been at it for a couple years now. They love each other romantically and as siblings, in fact the sibling bond is what let them trust each other enough to be each other's first time. Step-bro say he doesn't understand but he won't tell and he's happy for them. Sisters then surround him and let him know they have a way to help him understand since they have a sibling bond with him too.

Main thing is, I wanted to try and come up with a story where a step sibling comes across a taboo act and winds up an equal member of it as the ones doing it see them as family.

For what it's worth, that sounds like a story I'd read. The step-sibling could be a great way to really flaunt the Taboo or forbidden nature of the incest, since he/she would be coming from (I'm assuming) a normal perspective. I'm seeing potential in exploring the less than comfortable social situations the trio would go through, after they all become lovers/fuck buddies.

I agree: the step sibling catching the incest in the act could be a good device, especially if some sort of blackmail or such were involved. Personally, I don't enjoy threesome stories as I find they are often written very sloppily and uneven (though, this is usually how they are in real life...), but I feel your ideas here have potential to be more than just a threesome story.

If you do end up writing about some of your ideas and find yourself in need of an editor, Feel free to drop me a line.

Best regards
PK

When was the step-sibling acquired? Have they been family long or only for a few weeks? They're likely to gain step-sibs every time a parent remarries. Could get crowded. But a new relative isn't the same as someone you've grown to think of as your brother or sister.

I may eventually finish writing a story based on reality -- they bought my big split-level house to move into -- of a widower with three kids marrying a widow with four, all 18+ because LIT rules. It'll be Group Sex, not Incest, because no blood relatives fuck each other, only their brand new step-kin -- sibs and parents alike. With threesomes.

Expanding on the OP, let's have widower Dan (with two young kids) marrying divorcee Ivy (with two young kids) who dies soon so Dan marries widow Sheri (with two young kids.) Fast-forward a decade till the kids are all 18+ and horny. Blood and non-blood, they suffer and enjoy the usual desires, angst, manias, and discoveries.