A core is very hard and somewhat resistant to damage, though a solid strike from a Progressive Knife is enough to destroy one. Physically, cores are actually fairly brittle, and when damaged shards chip off and the core fractures, visually behaving like crystalline material.
The core appears to uniformly serve as a container for the soul of the Angel or Eva.
In humanoids such as Adam, the Evas, and Sachiel—and even Zeruel and Israfel—the core lays exposed in the solar plexus region. (Lilith, alternatively, has no exposed core. Being outside of Adam's "family", she may not possess one at all.) The organ is positioned variously in other Angels. Examples:
- Shamshel: "Throat" region, exposed
- Ramiel: Centralized location, internal (never seen)
- Gaghiel: Back of mouth, visible with jaws open
- Sahaquiel: Center of "eye", exposed
- Arael: Between "brachial" wings, free-floating
Leliel's unusual nature results in what appears to be a flat (rather than spherical) glowing core within three-dimensional space. Ireul presents another odd case in being a collection of many microscopic entities: Is there one "shared" core, or does each individual possess its own? The nature of the cores possessed by the amorphous Bardiel and Armisael is also unknown.
For Yui and Kyoko's Contact Experiments and Eva piloting, the ventral end of the Entry Plug is inserted into the core. According to preparations made prior to Yui's Contact Experiment, a cylindrical cavity is excavated to permit the accommodation of the plug (21'). Eva cores also seem to generate their own supply of LCL (20, 23', 26').
Unit-01 uniquely possesses two to four small core-like structures that are situated around her main core. Since it is implied that NERV can alter or even manufacture cores (or some form of) the smaller cores might be artificial inserts, for purposes unknown. One suggestion is that the small cores around the main core serve as a complementary purpose, or as a backup to the main core.
At Second Impact, a black circle or ellipse appears in Adam's solar plexus region, apparently smaller in size than the core itself (OP, 12). Possibly related, a dark circle (sphere?) manifests within Unit-01's core shortly before she fuses with the Spear of Longinus (26').
Rebuild of EvangelionEdit
In Rebuild of Evangelion, the entry plug is actually depicted being inserted into the core in imagery. Within the Rebuild continuity, the core is identified as the origin of an Eva's A.T. Field, as the display graph in the Sachiel battle identifies the A.T. Field as originating from the core and Entry Plug of Unit-01.
Evangelion 3.0 introduces the full body core type Angels, who are resilient to most damage and regenerate quickly unless massive damage is done to them instantly, such as being eaten whole by Evangelion 13 or Evangelion Unit-02 self-destructing when holding one. The Evangelion Mark.09, the Twelfth Angel, and it is implied that Evangelion-13 have full body cores.
- While the characters consistently refer to the core as "koa" ("core"), the term koukyuu (光球) is sometimes observed in print. Koukyuu means "photosphere" ("a sphere of light or radiance") and is apparently in reference to the core's luminescent properties.