Druckmann felt that the story of Joel and Ellie's relationship in The Last of Us dealt with survival, loyalty and love, and that Ellie and Riley's relationship in Left Behind deals with similar themes.
Druckmann merasa bahwa kisah hubungan Joel dan Ellie di The Last of Us ditangani dengan kelangsungan hidup, kesetiaan dan cinta, dan bahwa hubungan Ellie dan Riley dalam Left Behind penawaran dengan tema yang sama.