Ah, yes. That's the expression I live for in my projects. Not the look of defeat. No, that is far too common. Nor the look of terror, though I admit it makes me tingle. No, no. You see, David, I live to see that look of defiance. Yes, just like the one you're giving me right now. Why? Because it's so deliciously out of place on that increasingly pretty face. And on that body, which is now so clearly female. I wonder what you'll look like in a month. Six months? A year? Skirt and heels and a blouse... With a bra, of course. I doubt you'll remain a perky B-cup forever, my dear. But I suppose we'll have to wait and see. 
Why?
That's always the question. Understandable, I suppose, but so dull. All right, all right. I'll tell you. You see, I know all about you, David. I know that you're a philosophy major--ha!--at the university. I know that you spend your nights in a dorm room mostly playing video games and getting high on marijuana. But more importantly, I know that you have a secret.
What do I know? I know you like to watch women. You sneak into places you shouldn't be and watch. You watch them undress, shower, even pee. You watch them masturbate. You watch them fuck.
You'd admit to being a pervert, maybe, but nothing more. "I just watch," you'd claim. "I don't hurt anyone." Liar.
The truth is that you want to be with those women. Not just watch. You want to touch them. To kiss them. To fuck them. 
But you can't. You're too afraid for now.
But yours is the start of a horror story, David. You may not be aware of what you were becoming, but if I hadn't intervened then in ten years, maybe more, you would have become a monster. A monster that would have no trouble with hurting people. With hurting women.
What's that? You don't believe me? That I'm just some crazy woman making up stories to justify my actions?
Maybe you're right, David. I can't be sure. But, frankly, I'd rather be wrong than risk finding out. Now that you're a young woman--or close--you have a far better chance of escaping that fate than if I'd left you alone.
I know you want to say something. You want to tell me I'm crazy. You want to say that I'm the one who's the monster. You want to say that I'm the one who's hurting you.
Well, yes. I am. But a monster who fights monsters. Now, come, let's get you into your new room. Don't worry, there's a big mirror there. You can watch yourself change...