Elmer von Bismarck is Kai's classmate at the military academy.
Elmer is a shy, polite young man. He is helpful to everyone, which is how he and Kai became friends. He is mentioned to be good at battle tactics.
Elmer's father was in the navy, so he joined the military academy as well in order to become a military man one day.  There, he became acquainted with Kai through helping him whenever he gets in trouble.