I suspect that Alendi, the man Rashek killed, was himself a Misting—a Seeker. Allomancy, however, was a different thing in those days, and much more rare. The Allomancers alive in our day are the descendants of the men who ate those few beads of Preservation’s power. They formed the foundation of the nobility, and were the first to name Rashek emperor. The power in those few beads was so concentrated that it could last through ten centuries of breeding and inheritance.
