No. not Alex P Keaten and his sister Mallory (who I did think was hot back when I was around 16) but a story based on an entire family with a fetish for bondage and incest.
I'm not talking whipping, hot wax, punishment type of bondage, but tickling teasing playful erotic bondage(although a couple of good hard orgasms with a wand for the ladies would be fun)
Maybe the mom and sis always have a Friday "girls movie night" while dad works and the son is usually out. He ends up coming home and while he is walking by the sister's room hears moaning.
he peeks in and sees sis tied to the bed moaning and pleading while...
her mother lies between her legs teasing her pussy with a couple of vibrators. Son is appalled yet turned on. he doesn't think they notice and he watches then goes to bed, jerks off and falls asleep.
He wakes up just as his sister and mom fastens his wrists to the bed and they strip him and start teasing him until he is begging for them to take care of him.
It can happen another way, that is just a quick idea. I do like the idea of the brother initially thinking he doesn't want to, but mom and sis are pretty persuasive.