I've been having this idea in my head for a while, and so, here it is:
We have a family. This family has a secret-they are demons. But they aren't born that way-they start as mostly humans with a little extra (they're stronger then average, faster then average, smarter, etc). The kids know this, due to mother and father having told them when they were young. When the children become adults (i.e. reach 18), it becomes possible to turn them into full demons like the parents-with a little bit of incestuous loving.
In this case, I want to play the Father giving his now 18 daughter what she needs to be changed. Aside from the above set up and me playing the father to your daughter, everything is negotiable. Want it to be extreme? Fine. Want it to be a little lighter? Also fine! PM me and let's work out a few ideas!