Characteristics
The Evas were designed similarly to the Japanese folklore creature Oni. Although they were originally assumed to be giant humanoid robots, the Evas are actually cyborgs, integrating a mostly biological being with a substantial mechanical infrastructure, including a capsule called an "entry plug" in which the pilot sits and controls the Eva's actions, though the extent of this control can waver. The only people who can pilot Evas are fourteen-year-olds whose mothers have died after Second Impact, who are chosen by the Marduk Institute and designated in numeral order as "children" (i.e. First Child, Second Child). The reason of this is not explained for some time, until it is revealed that the souls of the pilots' mothers are put in the Evas so they can form a psychic link with the pilots that allows the pilots to control the Evas. Once connected to the Eva, the entry plug is filled with a translucent, breathable liquid known as LCL, which allows the pilots to electrochemically control the Evas. LCL is repeatedly mentioned to smell like blood and revealed later on to be derived from the blood of the second Angel, Lilith. The pilots wear uniforms called plug suits and devices called interface headsets on their heads to achieve better synchronization with the Eva. Although the Evas wear armor, their most significant defense is the Absolute Terror Field (AT Field for short), a form of force field which protects the Eva from all forms of conventional damage and can be used to disrupt an Angel's AT field.
All the Evas but one are derived from the first Angel, Adam (in the Book of Genesis, Eve is created from one of Adam's ribs). Unit 01 is unique in having been born from the second Angel, Lilith. With these revelations, the true purpose of their armor is also revealed - it is actually to constrain and control their movements. Based on production sketches from Evangelion 1.0 Complete Records Collection, the Evas are 80 meters tall; this presumably applies to the humanoid angels as well.
To power their massive frames, they use internal batteries, an umbilical cable, or an S² engine. Auxiliary batteries can be attached to extend an Eva's unplugged endurance. The Evas are controlled through their psychic link to the pilot via a combination of hand controls in the entry plug and direct nerve impulses that links to the pilot's plug suit and interface headset. The pilots also receive feedback through this connection, even experiencing the pain of damage inflicted on the Eva. This pain depends on the pilot's "synchronization" ratio in the Eva. The higher the ratio, the more pain the pilot is likely to feel, but also the better they synchronize with their Eva, the better they can control it. This is the reason why the pilots often undergo routine synchronization tests, in order to measure how well the pilots are able to synchronize with the souls that are bonded within the Evas. The Evas can also be controlled by an autopilot system, the Dummy Plugs, which are based on the thought patterns of either Rei Ayanami or Kaworu Nagisa. Evas can also lose control in certain circumstances and go "berserk", such as when the pilot is under extreme stress.
The Evas fight with their arms and legs, but they can also wield and use a wide variety of giant conventional weapons. Additionally, each Eva has a bladed weapon known as a "Progressive Knife" in their shoulder blade.
Read more about this topic: Evangelion (mecha)