The Idea Factory - Superhero's Apprentice
This one just kind of fell out somewhere. It might be from Reacher (you know which scene). It might just have been my weird brain.
In a world where there is a single superhero watching over everyone, a man brings his only daughter to his stronghold, offering her to him as his apprentice. The thought is that she would do whatever he needed around the house as he trained her for superhero work. Maybe that she would be able to gain his powers just from being around him or that he would offer her the secret to them. He has no interest in an apprentice, or an assistant, and it becomes something of a reverse Beauty and the Beast. The superhero spends most of his time alone, though, so he does appreciate the company. They eventually fall in love, but then she becomes something of his kryptonite. They try to keep it secret at first, but her father comes back at the head of a resistance army, coming to kill him. Did she know? Was she in on it? Does she power up to defend him?