Hi,
I am not an Admin, but I suggest that you start with the published rules for the site. After that, I recommend discussing your question with an Admin. For your convenience, here is a link to one of the relevant site rules.
User Conduct
You agree not to use the Wikia Service to:
[...]
2 - Post or transmit any content that is obscene, pornographic, abusive, offensive, profane, or otherwise violates any law or right of any third party, or content that contains homophobia, ethnic slurs, religious intolerance, or encourages criminal conduct;
Hey Cutterfish,
I'm pretty sure that you can have sex in the story, but so long as it's not explicit or focused around that one aspect. i.e. no stories that are just sex scenes or vehicles for sex scenes.