The Sentients
Adaptive machines built to prepare Tau that became a conscious people during the voyage.
TAU · ADAPTATIONFULL SPOILERS
Body and family
Small combat units can be parts of larger mother-minds. The family bond between Hunhow, Praghasa, Natah and Erra is no copy of human biology, but it is real both emotionally and politically.
The Void weakness
Crossing the Void wounds their capacity to reproduce, and its energy is the blind spot of their adaptation. Tenno superiority in the Old War rests on that limit.
They are not one will
Natah choosing the Tenno, Hunhow shifting his alliances and Erra turning on Ballas all show that family duty and individual will can collide within the people.