Doppelganger

Doppelgänger (n.)
1. A ghostly double or counterpart of a living person
2. A ghostly double of a living person, especially one that haunts its fleshly counterpart.
3. A spiritual or ghostly double or counterpart; esp., an apparitional double of a living person; a cowalker.

Inspired by this story and the music video for Thirty Seconds To Mars' The Kill.

Fiction, not fanfic.

Enjoy.