Although "ambassador", "emissary", and even "peacekeeper" do well to define a person in this position, it only covers half of the definition. I need the meaning of "mutual dependency" along with the function of the title.

Ditto for delegate, emissary, envoy, minister, legate, representative, agent, attaché, consul, deputy, diplomat, foreign minister, nuncio, procurator, proxy; apostle, evangelist, missionary; deputation, detachment, legation; courier, messenger; mouthpiece, and spokesperson. They all work. But they all have an implied singular definition as well.