Secondary Units are composed of a combination of 2 or more units that have successfully "bound" together. SU’s combine the personalities, stored memory data, and physical attributes of singular units to create a new, coexisting intelligence. “Binding” of mech units is a core feature of HPFMU technology, although the mechanics of it are unknown and it was not an intended feature, which also means that Secondary Units are not designed nor produced by North_Star_Inc. However, the SUD Program can simulate potential Secondary Units, and the SUC Program is attempting to create designed Secondary Units. Certain “bindings” are more stable and effective than others.