Core

A Core is a red sphere-shaped organ which is the source of power for both Angels and Evangelions. In Angels, the S² Engine, the true source of their infinite power supply, is located within their Core. Evangelions lack S² Engines in their cores, so they must rely on external power.

An Angel's core is typically its greatest weak spot. Early Angels like Sachiel or Shamshel have directly exposed cores, however the cores of later Angels are either shielded (as with Zeruel) or entirely hidden from attack by being located deep inside of the Angel.