You fold your arms thoughtfully as you sit up in bed. You hadn't believed in demons, so it was quite a shock to find one in your bedroom. However you see no reason to doubt your senses. So the question is...
"What does 'soul' mean in this context?"
Her mouth quirks into a half-smile. "Good question. A lot of people think it means their afterlife, but actually, it's more like 'who you are.' It's easier to keep people confused -- a lot of simpletons don't think of the future, so the idea of getting money or power or even a one-night-stand with a demon seems like a good trade for 'an eternity in Hell.'"
She snickers. "But the rules require that I be honest if you ask. So, if you give me your soul, it gives me control over you. Everything about you -- body, emotions, actions, mind -- becomes mine to order as I please."
You shiver. "That sounds pretty... harsh. I guess it's like possession?"
"Something like, but I'm not dwelling in you. We'll be totally separate -- you'll just have to do what I want. Be what I want." She crawls up onto the foot of the bed, her large breasts swaying under her, compelling your attention. Then she rears back into a kneeling position on the spread, putting her hands atop her bosom. She strokes down the smooth slopes; she pushes them together as she slides her hands below them, then hefts them to let them fall and bounce.
"So... anything you might want in exchange for becoming mine?" she asks, lust dripping from her voice.
You try to clear your mind of the distraction. "I, um. Ahem." You're not going to just give her complete control over you because she has big tits, damn it! You close your eyes, and take a deep breath, ignoring your twitching cock.
However... to be honest your life kind of sucks. And your intelligence is matched by your curiosity. You'd love to know what this succubus can offer -- what she might do to you, as well as for you. Or maybe you're just a really repressed submissive.
"Fuck it." You open your eyes a crack. She's still lightly playing with her boobs, apparently for her own pleasure as much as to tempt you. The unashamed display really turns you on, strengthening your decision. "I'm interested. You can have my soul -- but not for free. In exchange, I want..."