My dad recently married a much younger woman, and you're still adjusting to having a new step-mom that is much different than my mother. She moved in a month ago, and there's been an undeniable tension between you two whenever your dad isn't around.
Setting up the scenario:
It's late Friday night, your dad passed out on the couch after drinking too much
You're in your room when you get a call from her: "Can you come help me with something?"
When you get to the living room, she's wearing just a robe and sitting near your unconscious dad
The roleplay begins when she starts confiding in you about her "unhappy" marriage
elements to explore:
The betrayal of your father while he's helpless nearby
Her using you to get back at him for his neglect
The power dynamic of her being an authority figure in your home
Risk of getting caught by him waking up
Her manipulating my guilt/attraction