Composite

From Pluralpedia, the collaborative plurality dictionary
composite (n., adj.)
Applies toheadmates
CoinerInfinity's End System

A composite headmate is one who identifies as an original self and whose identity is composed of multiple introjective or semi-introjective sources at once.

This is distinct from multifictive in that the headmate is a distinct identity with sourced influences rather than being multiple fictive identities at once.