Spike: The Demon Hunter

Spike dies and the Powers That Be are indecisive of where to send his soul. As a solution they send him back as a supernatural human to Season 1, in a timeline with no William The Bloody. His memories have been stripped and fake ones have been placed, making him a Demon Hunter, working with one Rupert Giles for the Watcher's Council. (Response to Esm3rald's Challenge.)