Mix soy sauce, mirin and sugar together in a small bowl, and set it aside.
Husk and clean corn.
Grill corn over medium-high heat for 12-14 minutes turning and moving around every 2 minutes or so, until some kernels are starting to char.
Brush the soy sauce mixture liberally to one side of the corn and turn it over to grill the soy sauce coated side for 2 minutes. Brush the soy sauce mix on the other side of corn and turn it over to grill for another 2 minutes.
Garnish with shichimi togarashi (optional). Serve immediately.