With summer starting, I have a little more time to write. Most of my ideas are taken at the moment, but more will be posted soon.
2. Star Wars: Former Rivals. Three years ago, my character and yours were apprentices for a very powerful sith lord. In order to inspire intense competition, he told both characters from the beginning that he would pick one of our characters to be his heir, and the other would endure a lifetime of suffering. My character ended up winning out. Yours was taken away and he hasn't seen her since.
Now a sith in his own right, my character senses a familiar presence in the force while dropping off a prisoner to an interrogation facility. As he investigates, he finds your character. She has spend the last three years enduring very severe forms of torment using the force and technology. She has no memory of her old life or the strong individual she used to be. All she knows is that when she is given a master, obedience to that master brings a reduction in suffering, while disappointing a master brings suffering. Perhaps she has even been implanted with a chip that allows a master to give her various degrees of pain or pleasure.
My character takes her as his slave, hoping to use her as a status symbol and to pay her back for the years of fierce competition she gave him. At first, he takes pleasure from making her show how broken she is, but over time he starts to feel compassion for her. The relationship can evolve from there.