No specific information is given about Rei's origin or heritage. Ritsuko Akagi states that Rei was born in a certain room deep in the lower levels of NERV headquarters, but this is all that is explicitly revealed in the series about her creation.[1] The Red Cross Book stated that Rei was created from the "salvaged remains" of Yui Ikari after Yui's absorption into Unit-01 in 2004. The connection between Rei and Yui is implied a few times during the series.She is the First Child.