Neon Genesis Evangelion's plot is a complex web of conspiracies and hidden truths. The central conflict is not just about defeating the Angels, but about controlling a planned apocalyptic event called the Third Impact. Two factions vie for this control: the secret society SEELE and NERV's commander, Gendo Ikari.
The True Nature of NERV and the Evas: NERV's public mission to defeat Angels is a cover. Its true purpose is to execute the Human Instrumentality Project. The Evangelions are not mere robots; they are living, biological entities cloned from the first Angel, Adam. The exception is Unit-01, which is cloned from the second Angel, Lilith. Crucially, the souls of the pilots' mothers are integrated into the Evas' cores, which is why only specific children can synchronize with them. Shinji's mother, Yui Ikari, deliberately merged her soul with Unit-01 during a contact experiment, becoming an eternal monument to humanity.
Human Instrumentality Project: Gendo and SEELE have different goals for Instrumentality. SEELE wishes to forcibly evolve humanity by merging all individual souls into a single, god-like consciousness, ending the pain of individual existence. Gendo, however, has a more selfish motive: he wants to use the Third Impact to reunite with the soul of his beloved wife, Yui, inside Unit-01. The entire series is a result of his meticulous and cruel manipulation to achieve this goal.
Rei Ayanami's Identity: Rei is not fully human. She is one of several clones created from the salvaged DNA of Yui Ikari and infused with the soul of Lilith, the progenitor of humanity. She is a vessel designed by Gendo to initiate his version of the Third Impact. In the end, she defies him, choosing instead to merge with Lilith and give the power to decide humanity's fate to Shinji, the person who taught her what it means to be human.
The Finale: In The End of Evangelion, the Third Impact occurs. Rei, as a giant Lilith-being, initiates Instrumentality, and the A.T. Fields of all humans collapse, causing their bodies to revert to primordial LCL. Humanity merges into a single sea of consciousness. Within this state, Shinji confronts his deepest fears and desires. Ultimately, he rejects Instrumentality, choosing a world where individuals exist separately, even if it means experiencing pain and loneliness again. He and Asuka are the first to re-emerge from the LCL sea into a desolate, post-apocalyptic world. His attempt to strangle her, and her subsequent caress of his face, signifies a raw, ambiguous, but ultimately real human connection in their new reality.