If the neurons in his brain are dissolved as is his entire brain we even have Misato walking around in it (the actual physical stuff) and he can remember have a self image but can not interact he also had a pattern sepia soul that they could sort of interact with.
Abouth the "stay with a single decision"
You claimed Rei's memories are backed up and that is the reason Rei doesn't need to learn to speak and do potty training etc.
Another alternative is that Gendo is perfectly capable to feed baby Rei a 5 year old soul so that she now has those basic skills.
Another alternative is that Yui had a talk with Lilith and seduced her to explore the world and interact with her child lilin and gave her the basics. It explains Rei's intrest and why Rei knew german (Yui did) Sure some of the memories got lost or locked away to experience a more normal life I guess(Unit 01 was still attached to lilith at the time and I don't think you could extrat lilith soul against her wishes [without creating third impact])
All these examples are just to show that theirs alternative ways how Rei got her memories and the best we could do is say we don't know.
Kaworu knew less then you think. He knew what he was, in the manga he mentiones the death sea scrolls so he might have read them. Rei knew more then she tought if Kaworu remained her of it.
Soulless doesn't mean dead in the NGE universe look at the reiqurium the spare Rei's aren't looking in random directions most are focussed on the people that came looking at them neither are they expressionless they rather respond well to the external stimuli.
to IgRAzm
I agree Rei III merged with both Rei II and Rei I but Rei I itself was split between Rei II and unit 00 , So if I say Rei III is the merger of Rei II and unit 00 this includes all of Rei I but also any experiences unit 00 might have had, Correct?
Rei, I believe, is better understood, and the process of her receiving the memories after dying has to be artificial because she didn't know what happened
it is the has that botheres me I have 2 alternatives allready, that has should be a could and that's just to say we don't really know.
and she perhaps begins to understand that he didn't treat her the way she deserved to be treated,
In the series Gendo let her clean out her appartment and then she mostly just sits on a stool waiting for third impact to start? Shinji never says a positive thing to her and activly avoids her, Rei also does not choose Shinji over Gendo in the series, the scene you refer to was from the series.
Gendo and Rei's relation is honnestly weird and in suspence of disbelieve (if I had to rewrite a 3 second part of the series I would have a scene where Gendo ejects Yui's entry plug during her contact experiment with another 1.5 seconds I would have Gendo sitting in LCL cradling Yui's plugsuit copying Misato with Shinji and with a other 2 seconds have Gendo stare at unit 01 still attached to Lilith) but that's fan fic stuff and mods don't like that.
I also agree Naoko worked on unit 00 and unit 01 but it was Yui who was in charge, but she never worked or met Rei (until she was apparently 5).
You are right that Fuyutsuki did not "create" Rei, deliverd comes closer I think. I don't think it's a figure of speech as it is now my turn to say who else would have done it. Gendo isn't qualified, Naoko wasn't involved theirs potential for a small group of unnamed technisians but Fuyutsuki was potentialy capable and said that he did it. He most certainly has not any sort of parentel relationship with Rei and the same goes for Rei.
and I don't see how their worldviews are similar
episode 6 (16:23) why does Rei work for NERV (pilot the eva)? Because she is bonded to it and bond to all people I have nothing else, why does Fuyutsuki work for NERV? episode 21 (15:10) Gendo implies Fuyutsuki's reasons are to create a future for humankind. These are more similar then anyone else including Gendo's nihilistic views.
Their both also right hands of Gendo.
The book that Rei is reading involves genetics and philosophy and could be a reference to Yui's study field of metaphysical biology but that was also the field the Fuyutsuki teached.
Fuyutsuki is rather cold but has the best intrest of humanity in mind, the same could be said of Rei. I think their world views are quit similar.
Now I've written all this and didn't even mentioned Rei's age :/
So again I think theirs no defined age for Rei and it's mostly a point of view.