Set in a post-apocalyptic 2015, the series follows Shinji Ikari, a teenage boy recruited by his estranged father to pilot a giant biomechanical machine called an 'Evangelion.' He must fight mysterious beings known as 'Angels' to prevent the destruction of humanity, all while battling his own deep-seated psychological trauma.

While they look like giant robots, Evas are actually cybernetic organisms created from the genetic material of the first Angel, Adam (or Lilith, in Unit-01's case). They are encased in armor to restrain their power and require a human pilot to synchronize with them. Each unit also houses a human soul, which allows for this synchronization.

It is the secret goal of the organization SEELE and Gendo Ikari. The project aims to forcibly evolve humanity by merging all individual human souls into a single collective consciousness, eliminating the 'AT Fields' (barriers of the heart) that separate individuals and cause loneliness and pain.

Angels are mysterious, powerful entities descended from Adam, the 'Seed of Life' that landed on Earth billions of years ago. They attack Tokyo-3 to reunite with Adam (or Lilith), which would trigger a cataclysmic event known as the Third Impact, potentially wiping out humanity.

The Second Impact was a global cataclysm that occurred in 2000 when a human expedition in Antarctica contacted Adam. It caused massive flooding, climate change, and the death of half the human population. Officially blamed on a meteorite, it was actually caused by the awakening of the first Angel.

The original 1995 TV series (and its movie finale 'The End of Evangelion') tells the original story. The 'Rebuild of Evangelion' is a four-movie series (1.0, 2.0, 3.0, 3.0+1.0) that starts as a remake but diverges into a completely new timeline with different plot points, characters, and a new conclusion.

Instead of focusing on cool robot battles and heroic pilots, Evangelion explores the realistic psychological toll of child soldiers. It deals with depression, trauma, and dysfunctional relationships, often subverting tropes by showing the pilots suffering rather than triumphing, and presenting the 'robots' as terrifying monsters.

It is a metaphor used by Misato to describe Shinji's behavior. Like hedgehogs seeking warmth but afraid of pricking each other with their quills, Shinji desires human connection but distances himself from others to avoid being hurt, resulting in a cycle of loneliness and isolation.

The final two episodes of the TV series take place almost entirely within the characters' minds, abandoning the external plot for an abstract, introspective psychoanalysis. This was due to budget constraints and creative choices. The movie 'The End of Evangelion' was released later to provide a more traditional (and apocalyptic) conclusion to the plot.

The recommended order is: 1. Neon Genesis Evangelion (TV Series, Episodes 1-26), 2. The End of Evangelion (Movie), 3. Rebuild of Evangelion movies (1.11, 2.22, 3.33, 3.0+1.0). This covers the original masterpiece and its modern reimagining/sequel.