I used to be huge into writing so I looked through some old drafts for my favorites. I originally had started writing the outline the story takes and realized that that would be a bit much to write.
The idea was based around a girl's brother being murdered. One day she meets a man who reminds her of her brother and then she starts dreaming of the day her brother was shot, but from her brothers vision. Starting in the day sometimes, she gets visions that she's seeing from somebody else's perspective. One day, she sees the man again, he looks oddly like her brother this time. The dreams persist, she feels pain, emotions, has memories that she didn't experience. The ending is where I didn't have this idea fully fleshed out. The main idea was that it would be revealed that since they were twins (and this world is slightly magical by the way), when her brother was shot (something magical happened as well), that part of her soul went with her, and the rest with the man who was trying to take it.
Basically, the TLDR is that a girl's twin was shot and when the murderer was extracting his soul, part of it went with the girl so she was then connected to the murderer.