Everyone assumes that Luke was the one to kill both Vader and Palpatine. The Dark Side, wary of Luke's presumed power, but wishing to harness it somehow, plan to kidnap any children that Luke may have. When it is clear that no children are forthcoming, they steal Luke's DNA, creating a clone-of-sorts: Rey. However, her carer, feeling sorry for the child, escapes with Rey and drops her off on Jakku, before the carer is killed by the First Order. Cue the events of TFA, with added suspicion from Luke and Leia as to the identity of this girl who resembles them so much.