Core

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The core is a headmate with a direct connection to the body's pre-plural self. Not every system has one, and not every system had a point at which they were not plural.

The core often inherits the personality, identity, and/or memories of the pre-plural self.

Related Terms
The host is the headmate who is most active or most responsible for day to day activities, which can be distinct from the core. Some systems also have an original, or a headmate that existed before becoming plural; these are more common in thoughtform systems.