As with other "Evangelion" characters, Anno transposed aspects of his life into her character, including the choice to not eat meat and maintain a vegetarian diet. He also took inspiration from Sigmund Freud's psychoanalytic concept of Oedipus complex, since "there was this replacement by a robot, so the original mother is the robot, but then there is a mother of the same age, Rei Ayanami, by [Shinji's] side, who's also by the side of the real father". In a discarded draft of the character background, she was a more sensual character than her final version. Sadamoto, unlike the more frank and explicit Hideaki Anno, decided to give her a much more "enigmatic" and bland eros. According to Sadamoto and assistant director Kazuya Tsurumaki, she was conceived as an alien entity, but staff later went on to make her at least genetically human; according to them, Rei should have had both the human genes of Yui Ikari and the genes of the first Angel Adam, associating her condition to a Devilman, a hybrid presented in the manga "Devilman" by Go Nagai.