Demon (Sterek AU)

Stiles was trapped within what used to be his body, and the remains of his once happy mind. He was broken and he couldn't be fixed. He was being overtaken by something so out of his reach that he had long given up and most of the time, Stiles wasn't in control of anything. He was a spectator watching through the eyes of someone else. What he needed was a savior, and when no one else would and when no one else could, Derek Hale came along and tried to free him from his cage. Derek Hale was determined to save Stiles from himself.