9. Caitlin (Heroes)
Peter Petrelli was an all-round decent guy whose powers could well have overwhelmed him. Peter was a power-empath; he absorbed the abilities of other super-powered people just by being near them. This also counted for Hiro Nakamura, whose ability to manipulate space and time allowed him to travel into the future.
During the second season, Peter wakes up in Ireland to find that he has no memory of who he is or how he got there. He's taken in by Caitlin, whose criminal brother causes some trouble. Ultimately, Peter accidently drags Caitlin to the future, a version of 2008 where 93% of the Earth's population have been wiped out by the Shanti virus and the survivors live in quarantine zones.
Peter and Caitlin are hosed down and processed. Peter is extracted by his mother Angela, who helps him to overcome his amnesia. While he is walking down a corridor, he sees Caitlin in a line of people being deported and attempts to get her out, but instead he transports himself back in time again.
So this poor girl falls for a mysterious amnesiac, gets time-travelled into a nightmare future and just abandoned?
C'mon Peter, you're meant to be a Hero, aren't you? Since that timeline never came to pass, did Caitlin cease to exist?