Thanks [@Silver Fox] for clarifying.  That is correct, koa is what was traditionally called deputy.
[@Ambra] The chieftains (chiefs) will be NPCs out of necessity, and the wavetribe koa is taken.  You are, however, welcome to submit a second CS as either Ashtribe's or Blazetribe's koa, or Blazetribe's Shaman, if you would like.  Though these positions are a little more selective, I would encourage anyone who can handle two + characters to apply if interested.  As a sidenote, I say 'second CS' because every player must have at least one character in WaveTribe.

EDIT:  The koa's apprentice slot is open for all tribes as well.