Rei Ayanami is a fictional character from the Neon Genesis Evangelion franchise, created by Gainax studio. In the anime series of the same name, Rei is an introverted girl chosen as the pilot of a giant mecha named Evangelion Unit 00. At the beginning of the series, Rei is an enigmatic figure whose unusual behavior astonishes her peers. As the series progresses, she becomes more involved with the people around her, particularly her classmate and fellow Eva pilot, Shinji Ikari. Rei appears in the franchise's animated feature films and related media, video games, the original net animation Petit Eva: Evangelion@School, the Rebuild of Evangelion films, and the manga adaptation by Yoshiyuki Sadamoto.

Neon Genesis Evangelion is a Japanese media franchise created by Hideaki Anno and owned by Khara. Most of the franchise features an apocalyptic mecha action story, which revolves around the paramilitary organization NERV and their efforts in fighting hostile beings called Angels, using giant humanoids called Evangelions that are piloted by select teenagers. Subsequent works deviate from this theme to varying degrees, focusing more on romantic interactions between the characters, plotlines not present in the original works, and reimaginings of the conflicts from the original works.