No specific information is given about Rei Ayanami'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. The Red Cross Bookstated 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. Gendo introduces Rei to the NERV staff in 2010 as an "acquaintance's child" whom he is temporarily taking care of. In episode 21, Naoko Akagi says that Rei physically resembles Yui. The character model used in the 2010 scenes is based on development materials in which her age is only 4.
Asuka Langley Sohryu (惣流・アスカ・ラングレー[?], "Sōryū Asuka Rangurē") is a 14 year old fictional character from the Neon Genesis Evangelion franchise and one of the female main characters. Asuka is designated as the Second Child ("Second Children" in the original Japanese versions) of the Evangelion Project and pilots the Evangelion Unit-02. Her surname is romanized as Soryu in the English manga and Sohryu in the English version of the TV series, the English version of the anime movie and on Gainax's website. (evangelion.wikia.com)