The devil made a deal with her. Except he didn't tell her. He didn't tell the girl with the half-hearted smile that she was his. That they were formed of the same matter, the very same evil, because he didn't think she knew. He did. He knew. He saw behind the smile, saw behind the facade she used to hide herself in school. A facade, he believed, that she used to hide from herself, because he knew, he knew that the deep, burning fire that formed his entire being was the same fire sustaining her. He knew they were one and the same, instantly combustable figurative fire balls that could at any point destroy everyone and everything around them.
The deep, burning fire that formed his entire being was the same fire that sustained her. And after all, you can't fight fire with fire.
