Kaoru Nagisa
The pilot replacement of EVA-02.
Analysis:
Kaoru is sent to NERV as a replacement for Asuka as she gets unable to control EVA-02 anymore. His perfect synchronisation makes NERV suspicious and as they investigate they find out that Kaworu indeed is the 17th Angel. Kaworu becomes a good friend of Shinji, who opens his heart to Kaworu. As it becomes clear that Kaworu is an Angel, Shinji has to kill him, which remains in Shinji's heart as a traumatic experience.