Kaworu and Shinji (Relationship)
Though fans have speculated on the exact nature of Shinji's relationship with Kaworu, it is clear that Kaworu represents a sort of idealized figure to Shinji, as he appears out of seemingly nowhere when Shinji is completely desperate for any sort of connection with anyone, as all of his friends are either dead, unreachable or alienated from him. Kaworu telling him he liked him surprised Shinji as he is afraid of talking to Asuka, Misato or Rei, as Shinji has internalized his belief that nobody cared about him thanks to his own partly self-imposed isolation - afterwards, feeling that Kaworu has simply used him further reinforces this, as he thinks everyone is lying to him, because Shinji is unwilling to recognize the ambiguity and insecurity in other people, and the risk and uncertainty involved in reaching out to them himself, something Kaworu temporarily allowed him to ignore. Kaworu uses the ambiguous "suki" form which includes intimacy or friendship or anything more, and can simply mean "like" or "fond of", and that he is deserving of "koui" (好意), which means simply "good will" or "favor", not "koi", "love". When he mentions this to Misato later, Shinji also used the ambiguous "suki" form. This line has necessary ambiguity in order to represent Kaworu's own lack of understanding regarding levels of intimacy and societal norms, part of what shocks Shinji and allows Kaworu to bypass his barriers of self defense, as he isn't even aware those exist, as he himself has none. When Shinji is fighting Kaworu, he states Kaworu has betrayed him, just like his father did, indicating he might have been seeking a similar form of support from him, reinforcing his role as an idealization. This metaphorical meaning of his presence is emphasized further with the reappearance of Kaworu in End of Evangelion, when Shinji is traumatized by experiencing Misato's death and seeing Asuka's dead Eva, Shinji becomes desperate, but Kaworu reveals himself to be part of of Lilith to stop Shinji from going into a frenzy and allow Third Impact to begin, although Shinji only enters Instrumentality after Lilith reverts to Rei's form and melts by seeing a woman's breasts, when Yui asks him what he wishes for. Though the precise nature of their relationship is debatable and yet to be determined, Kaworu forms a strong connection with Shinji. His absence from Instrumentality and even the Congratulations scene when even characters like Aoba are present bring into question how much Kaworu affected him besides Shinji's own desperation. Shinji, in fact, seeking unconditional affection from everybody, unwilling to return their own needs, is a fact that has hindered Shinji's happiness throughout most of the series, and Kaworu, being a somewhat non-human character without his own emotional needs (whereas Rei had slowly developed those) is the only one that does that. Moreover, the way Kaworu treats Shinji as a sort of avatar for humanity also brings into question if his affection is directed towards humanity as a whole.
This, paired with the fact that Shinji had killed what he saw as a human being and someone he cared about, was part of what drove him into his state of absolute despair in Episode 25, in which he declared that he felt unworthy even of the piloting which had consumed his identity, thinking that if all he did was hurt and kill others, it was better to do nothing. By that, though, he may have condemned Asuka, who was fighting against the Mass Production Evangelions, to death. Had this not been the case, it is very possible he and Asuka could have defeated the Evas and stopped Third Impact altogether, a fact that greatly benefits SEELE. Shinji depositing all of his hopes for self-worth onto Kaworu, and having that fail him, also reinforces Shinji's notions that if he can't rely unconditionally on people and never risk rejection then he is not actually loved by anyone at all and everyone should just die, part of what motivates him to start Third Impact. In End of Evangelion, Shinji desperately seeks this same sort of unconditional affection from Asuka, and is still certain that he is unloved and unworthy, as he demonstrates he has in fact returned to his own childish beliefs about himself, even after the way Kaworu (whom he does not even mention) treated him, and other characters respond to him that he is in fact liked and treated nicely by them, but Shinji refuses to believe it. In contrast to Kaworu, when Shinji, in a similar state of desperation, asks for Asuka's own unconditional affection, Asuka refuses as she does not want to be an emotional crutch and an escape for him, and demands he gives himself to her as well, but Shinji is unwilling to give back any affection himself. Asuka says he doesn't really like anyone, as he doesn't even love himself. When Kaworu and Rei as Adam and Lilith state they represent the hope for understanding and love, Shinji replies it is just a pretense, but if he returns to the real world, at least there he will know his feelings are real.
- Some early fansubbers misheard this as "koi", but the scripts for this episode make it clear it is "koui". As for "suki", the original ADV VHS subtitle translation gives the word as "like," while Platinum and the English dub use "love." The Netflix release, translated by Khara, chose to use "like" again. Khara's own official translator has publicly defended this change, and the ambiguity it retains from the original text.