Eva-04 is the fifth Evangelion completed, the third "Production Model" Evangelion. It, and it's sister, Eva-03, were constructed in the United States of America. Eva-04 was constructed at Nerv's second branch base (Nerv-2) in Nevada. Nevada base was destroyed along with Eva-04 when the Eva's S^2 Engine failed while testing Episode 17. It was stated that the failed engine may have opened up a Dirac Sea which enveloped the Nevada base. It is also strongly implied that this may have merely been the result of an accident. The shock of this accident led to the United States immediately transporting Eva-03 to Japan, which in turn led to the events of Episode 18
Physical features
Evangelion Unit-04 is a Production Model Evangelion.
Although never seen on screen, production art featuring Eva-04 has occasionally been released by GAINAX. It is depicted as being silver in colour and roughly similar to Eva-03, and the preceding Eva-02 and rebuilt Eva-00 in armour design and physical stature. It uses the same 5-plate torso armour design, and the same shoulder mounted storage Pylons. Eva-04 is shown to have four small red-lensed eyes in comparison to Eva-03's two, and Eva-02's four large spotlight-like ones.
It's primary distinguishing feature is its S² Engine, likely to have been a restored version of what was recovered from the remains of the Shamshel in Episode 05.
Given that it is a Production Model, it is likely Eva-04 would have required a pilot. As it is never shown on-screen, the identity of the would-be pilot remains a mystery. In some spin-off materials, Kensuke Aida is depicted as being the Pilot of Eva-04.
Soul
A feature of all Evangelions is that the soul within them is the soul of the mother of it's designated Pilot. As a designated pilot for Eva-04 is never shown on screen, the identity of the soul can only be guessed at.
Given that some spin-off materials have shown Kensuke Aida as Pilot of Eva-04, and it has been mentioned that Kensuke does not have a mother (Episode 05), it is possible that the soul contained within Eva-04 could be that of Kensuke's mother.
Eva-04 in Rebuild
Eva-04 is shown in the teaser trailer for Evangelion 2.0 at the end of Evangelion 1.0: You Are (Not) Alone. A caption flashes up, listing Eva-04's presence, followed by a large red explosion. This would suggest that it will suffer the same fate as in the television version.
Notes
Eva-04: the Eva that never was. Note that it should be silver, not whiteEva-04 was never actually seen on-screen, however Gainax has produced production sketches of it revealing that it was identical in design to Eva-03, but colored silver (that is, "chrome"), with red and black highlights. The only full body image they ever produced of Eva-04, however, mistakenly colored it white instead of silver: other close-up images of Eva-04 show it as silver, and in the numerous Evangelion spin-off merchandise it appears in such as video games and action figures, it is always silver.
