Evangelion Unit-02 is an integral part of Asuka's identity. As the Second Children, Asuka constantly wears her bright red headset as a reminder to the world that she is the pilot of EVA-02! None of the other pilots are quite as synonymous with their Evangelion counterparts as Asuka is with hers. I've presented this section in a sort of FAQ to make it easy to understand for fans who are newer to the series.

What is an Evangelion?

The Evangelion were built by NERV to combat the threat of the invading Angels (massive, extraterrestrial entities that seem intent on recreating the Second Impact). At a glance, they appear to be giant robots but underneath the armored exterior is a living, breathing human genetically engineered from the cells of the first Angel, Adam. Although they are human-like, they do not possess souls of their own. Rather, they obtain souls through Contact Experiments, where a human comes in contact with the Evangelion and effectively merge together. With the exception of the mass produced models and EVA-00, the souls of each Evangelion belong to the mother of the child who pilots it.

In the case of EVA-02, it was Asuka's mother who performed the Contact Experiment. Unfortunately, while the experiment was a technical success, it tore Kyoko's soul apart. The maternal aspect of Kyoko's soul was absorbed by EVA-02 and the rest remained inside Kyoko herself. With her soul fragmented, Kyoko lost her sanity and ultimately killed herself. In The End of Evangelion, when Asuka first realises that Kyoko's soul has protected her all along, we hear both aspects of Kyoko's soul calling out to her, implying that the death of her body allowed her soul to reform as one.

What makes EVA-02 unique?

As far as Evangelion go, EVA-02 is unique in that it is the very first of the production models. EVA-00 was the initial prototype and EVA-01 was the first non-prototype test. EVA-03 and EVA-04, the two units to be produced after EVA-02, share the same general armor design but lack EVA-02's extra pair of eyes. EVA-02 also seems to differ from the other units in that underneath its armor, it has purple blood and grey skin.

Being a production model, EVA-02 comes equipped with an updated progressive knife and the shoulder pylon on its right side can fire deadly spikes. It can also make use of special adaptive equipment such as the D-type armor set featured in episode 10 that allows for an Evangelion to be submerged in lava. Like all other Evangelion units (and all Angels), EVA-02 also has its own A.T. Field (a protective barrier that only another A.T. Field can penetrate).

In the Evangelion 2.0, when Makinami Mari pilots EVA-02, she uses a passcode to unlock the restraints preventing EVA-02 from entering beast mode. Unique to the Rebuild films, beast mode allows EVA-02 to use more of its innate power, abandoning its humanity and taking on a more feral, animalistic appearance. We see Asuka activate EVA-02's beast mode again in Evangelion 3.0. Both Asuka and Mari are affected by EVA-02's use of beast mode in that they both begin to exhibit feral tendencies along with glowing green eyes.

What is synchronization?

Synchronization is the neural connection between the child piloting and the soul of the child's mother residing inside the Evangelion. In the case of EVA-02, the synchronization is between Asuka and her mother, Kyoko. The higher a pilot's synchronization score, the better they'll be able to control their Evangelion. Until Shinji surpasses her late in the series, Asuka has the highest synchronization scores among all pilots. Pilots also use interface headsets and plug suits to achieve higher synchronization.

An unfortunate aspect of synchronization is that pilots share the pain their Evangelion endures in battle. If an Evangelion's arm is broken in battle, the pilot will feel as if their own arm is also broken. In The End of Evangelion, we see Asuka actually bleeding from the wounds received by EVA-02 in the battle versus the nine mass production Evangelions. This appears to be a unique side-effect of the mass production models using man-made Spears of Longinus to pierce through EVA-02's body.

Why is Asuka so attached to EVA-02?

It's fairly evident that Asuka is very attached to her Evangelion; she outright refuses to pilot any other unit and she's very proud to be the pilot of the very first production model. Her own identity is tied very closely to EVA-02 and much of her pride and confidence comes from her ability to pilot it as well as her high synchronization rates with it. She feels that as long as she is the best at what she does, she has a solid place in the world and this gives her the confidence she needs to continue to live in the world.

Her specific attachment to EVA-02 is obviously because her mother's soul resides within the unit and despite her difficult relationship with her mother, Asuka still shares a close mother-daughter relationship with Kyoko. Asuka has no awareness of this relationship until The End of Evangelion however, so it's entirely subconscious if anything. At one point in the series, when Rei and Shinji are testing their synchronization rates in each other's Evangelion units, Asuka asks why she's not required to test her synchronization rates in any of the other units. Misato simply replies that they figured Asuka would refuse to pilot any other Evangelion than EVA-02 and Asuka agrees.

What is EVA-02's ultimate fate?

In The End of Evangelion, EVA-02 is launched into a nearby lake with the comatose Asuka inside to protect her. While she's inside of it, Asuka is able to connect with her mother's soul and comes back to life. Asuka then takes control of EVA-02 and begins to fight to protect NERV from the invading UN forces. EVA-02 fights on battery power; the first two minutes are used to utterly destroy the UN forces and the last three are to face off against the nine mass production Evangelion units.

In one of Asuka's most glorious battles, she defeats all nine mass production units before her EVA-02 runs out of battery power. Unfortunately, the mass production models come equipped with S² engines, allowing them to regenerate and run on infinite power. They get back up, spread their wings and descend upon EVA-02, devouring its bowels and carrying pieces of it all over the geofront. Asuka is still connected to EVA-02's nervous system and from what we see, she experiences the same wounds that EVA-02 suffers, leaving us to believe that she dies along with her Evangelion. The last we see of EVA-02 is its head left staring up blankly at the sky, watching the events of the Third Impact unfold.

At the end of the film, when Shinji rejects the Third Impact and Human Instrumentality, we see him return to Earth with Asuka at his side. She's alive... but we know nothing about EVA-02 or Kyoko's soul.