Holy night, family ‘bonding’ night

This is a story of two family members, one male one female.  Probably brother and sister, but could be father and daughter or mother and son.  There is incest, but the actual sex scenes with them will be rare, if not only in the beginning.

It is a world where most of the time incest is as taboo as it is for us.  But an exception is made one day a year. Adults are allowed, almost expected, to choose one opposite sex family member and sleep with them, including sex.  The holiday is meant to strengthen bonds between family, and remember an ancient time, the first humans, when all couples were much more incestuous.  But after the night is over, they get up and just treat each other as family.  It does not matter if they are already in a relationship/married/have children, it is forgotten one night a year.  They are not supposed to want children, but birth control is forbidden, and it occasionally happens and society accepts it when it does happen.  Optional if it does with our characters.

We will be starting with one of those nights.  The first night our characters have done such a thing.  Explore their confusion over the mix of taboo and holy act them having sex that night is.  But the focus of the story will be the aftermath, exploring how they interact with each other afterwards, and how they interact with others.  They will not do it again, unless we time jump/play long enough, that they try it again in a year, when the night returns.

That’s the basic idea, with quite a bit of flexibility.  We will each have a main character, but could play other characters around each of them.  There could be sexuality exploration too.  Maybe the woman prefers women, has a girlfriend/wife, but for the holiday, only MxF pairs are allowed.  Maybe one or both are socially awkward and this is their first time with anyone.  There are many ways this could go, though both will likely respect the taboo, incest scenes being limited to once a year in story.