In the battle with the Angel Armisael, Rei decides to sacrifice herself alongside Eva Unit-00 to save Shinji and destroy the enemy. After her apparent death, Dr. Ritsuko Akagi reveals she was born in Laboratory for Artificial Evolution's third branch, a place located under the lake Ashino and Hakone city. Her body with albino-like traits was created in absolute secrecy from the salvaged remains of Yui Ikari, a brilliant researcher who lost her life in a testing experiment by Evangelion Unit 01. Ritsuko also reveals that in the deepest level of Nerv's headquarters many Rei clones are kept, so that when one Rei dies, she can be replaced. When a clone is activated from a level named Terminal Dogma, although she remains characteristically distinct from all former incarnations, she is endowed with the soul of Lilith, the second Angel. In 2010, Gendo brought her first clone (Rei I) to the Gehirn base, the predecessor of Nerv and responsible for the development and construction of the first Evangelion units, introducing her as the daughter an acquaintance had entrusted to him. This first Rei was killed by Dr. Naoko Akagi, colleague and secret lover of Gendō. During her visit to Gehirn, Rei I got lost in the laboratory control room and met Naoko, calling her an "old hag", as if to provoke her. She then revealed that it was Gendo who called Naoko that. Naoko suddenly recognized Yui's facial features in the little girl's face and in an outburst of violence, she strangled and killed her, after which she committed suicide.