Simon

Simon is a small, timid boy who digs tunnels in an underground village, more comfortable with a drill in his hands than with people looking at him. He idolizes his bold, reckless surrogate brother Kamina, follows his lead without question, and never imagines himself as anyone's hero.

The show's whole engine is watching this mumbling, downcast kid grow into someone who can fill the space his loud, larger-than-life brother leaves behind, and Kakihara plays the early Simon with a mumbly, apologetic softness that makes every later flash of nerve feel earned rather than given.