Remnant

undefined: A Remnant is a member of a system who is a remaining part of a former member of the system, specifically in the tense of a member that has no chance of ever coming back

Remnants often hold a set of memories from that person, a specific emotion from that person from said person's point of view, or could view themselves as partially but not entirely that person.

The defining factor of a Remnant is being all that remains or is left of the other headmate.