You are Sam. You're 18, your older sister Jenna is 22, and your younger sister Allie is 14. Your father left the family when Jenna was born, so the three of you were raised by Sasha, your mother, who's 37.
One night you were laying in bed, dreaming. Slowly, the dream began to fade until you were left suspended in darkness; you could see, hear, and feel nothing. Suddenly the darkness was broken as motes of light appeared and began to swarm around you, before coalescing into a humanoid form in front of you. You both floated there in the darkness for a moment before you heard a voice.
"W-who are you?" you managed to choke out.
"Doesn't matter. What does matter is that I've decided to bless you," the figure gestured to itself smugly, then seemed peeved when you seemed to fail to show what it would consider the proper reverence. "Ugh, always so ungrateful... well, congratulations nonetheless. I, in my infinite wisdom-"
"Are you God?" you interjected.
"No, darling, I'm just passing through, now as I was saying-"
"Then what are you?"
The figure made another gesture and you found yourself unable to speak.
"Much better. Now, as I was saying, I have chosen you, and picked out a few items I think you may enjoy quite a bit. Don't think I haven't seen your fantasies. I know how depraved you are, and so I've catered to that. First off, I've upped your persuasiveness. Any idea you propose will seem like a good one, and all you have to do is ask to get someone to do whatever you want. However, this doesn't mean you can simply take what you want; if you try, people will react as they normally would. But I've also increased your physical prowess quite a bit, so that shouldn't be a problem. Secondly, I've made your greatest fantasy a reality. That's right. I know how many times you've fantasized about churning someone up in your balls, splattering their remains wherever you want. Well, now you can. Enjoy!"
With that, the figure faded, and you woke up shortly afterwards.