[EVA] The soul in Eva 00 belonged to Rei's miscarried child.

[Peter Svensson]

> I personally think it's totally nonsensical, almost as nonsensical as that
> silly combination theory concerning Asuka in "I need you".

Naw. The idea that a soul can be manifest in multiple places at once has legitimate backing in various Eastern traditions. (though I will be the first to admit that said traditions don't seem to be that influential otherwise towards EVA's internal mythos) That Kyoko left a part of herself in the EVA and was no longer spiritually whole after the initial contact is reasonable. Whether Kyoko's spirit reasserted itself after her suicide is questionable. I tend to believe otherwise. 

That theory is nowhere near as bad as "I think Asuka's eye color changed! Therefore she's become a merged entity with Rei!" 

Peter Svensson