Santô Hei 三等兵 is the initial rank of a trained soldier in the Star Army of Yamatai, and the starting rank of new Player Characters. The next highest rank is Nitô Hei. The rank below is Yontô Hei. In casual or combat situations is acceptable to just say “Hei” rather than the full rank title.
For a full listing of ranks, see Star Army Ranks and Pay Scale.