:The Succubus Fantasies:

"We need to stop this!" you announce. Something is happening and you're not in control and you don't like it. It could go very wrong.

Your sister stops and looks at you. "But I thought you said you were going to help me? Whatever's happening, I'm sure we can do something about it later. For the mean time, I need help with this food and we can't do that in these clothes. Come on!"

She starts to undo a button on her shirt. This is a point of no return. You're either doing this or not. What's it to be?