Theory and Analysis:Soul Divisibility
Soul Divisibility refers to an implied property of living beings' souls in Neon Genesis Evangelion allowing them to be split and the resulting fragments thereof contained in separate vessels. These may be the bodies of humans, Angels such as Lilith and Kaworu or Evangelion Units.
This property is implied, or seemingly observed at least twice and probably three times in Neon Genesis Evangelion. The first example is that of Lilith's soul, divided into the bodies of Rei Ayanami as well as Eva-00, as well as residing in her own original body. The second instance is the splitting of Kyoko Zeppelin Soryu's soul during her Contact Experiment with Eva-02 resulting in the portion of her soul which feels maternal love towards her daughter, Asuka Langley Soryu, entering the Eva's core, causing her to go insane and lose all recognition for Asuka following the experiment. The probable third time is the Angel Israfel, whose soul is likely split between its two cores when it splits into two beings.
In the case of Lilith, it is unclear as to what extent the Rei clones are cloned from Yui and to what extent from Lilith; indeed, the ambiguity concerning Rei's creation itself makes it difficult to tell what exact constituents Lilith provided towards Rei's conception. She seems to be genetically cloned from Yui, but made with Lilith's biomas: Particle-Wave Matter. However, it is possible that Lilith provided some of Rei's genetic code as well. It is made clear that Rei's bodies are clones due to her repeated appearance after dying in Episode 21 and Episode 23. In The End of Evangelion Rei III is shown to reunite with Lilith with the words "I'm home" ("tadaima") and Lilith replying "Welcome home" ("Okaeri nasai"), implying that part of her soul is still there to greet her. However, the fact that she has Lilith's soul can be deduced earlier in the series through her distinctive behaviour and unnatural appearance. Throughout the series, Rei acts in a manner seemingly detached from human nature, and constantly has trouble dealing with her own emotions, which she finds unfamiliar and sometimes incomprehensible. Judging by the fact that Rei was created in Nerv, and that the only living non-human being in Nerv's possession at the time of her appearance was Lilith, the conclusion can be reached that Lilith provided some material for Rei's existence, as well as parts of her soul.
It is also probable that the soul of Rei I, originally from Lilith, inhabits Eva-00.
- See Eva-00's soul for more details.
Kyoko Zeppelin Soryu
During Soryu's Contact Experiment with Eva-02, part of her soul entered and remained within the core of the Eva, not unlike Yui Ikari's absorption into Eva-01. It is there that the similarity ends, as whereas Yui's union with the Eva was a complete one both physically and spiritually, Soryu was not fully absorbed and emerged from the experiment physically unharmed. Still, it is clear that the experiment had inflicted a bitter and lasting effect upon her since she became highly unstable mentally, suffering from an inability to recognize her daughter and instead mistaking rag dolls for Asuka. The part of her soul within her was likely deeply traumatized, going through the pain of her husband's infidelity during her illness and she eventually committed suicide, hanging herself along with one of the rag doll “Asuka”s. Evidence suggests that this part of her soul was then salvaged and reunited with the maternal portion within Eva-02, as her voice begging Asuka to “die with me” is heard alongside her otherwise encouraging words telling Asuka she is still alive.
The Angel Israfel is an ambiguous case. It possesses a single core in combined form (two, in Sadamoto's manga) and two when it splits into "twins" capable of both operating independently and fully in synch. In the show, this ability could be explained by an innate ability to split and recombine a soul that was initially one.
Alternatively, it could be explained as a single soul possessing the ability to exist in two places simultaneously. Another line of thought proposes that Israfel is technically two individuals capable of combining and separating their bodies and souls at will. The fact that Israfel is classified as a single Angel is sometimes considered an obstacle to this interpretation, but given the case of the Lilin, there is a precedent for classifying multiple individuals with similar forms and capabilities as a single Angel.