Rachel Rosen is a Replicant, a genetically-enhanced clone. Deckard finds her while searching for Roy Batty and realizes that, although Rachel has been abused and discriminated by humans as much as Roy, Rachel isn't evil, and thus Deckard takes pity on Rachel and falls in love with her. When Deckard finds out that he himself is a Replicant, he and Rachel retire to the countryside, since Replicants have a shorter life span than humans.
Years later, Rachel died of unspecified causes, but before having a daughter with Deckard.