Step 1Place the rice and 1 1/4 cups cold water in a saucepan and soak for 30 minutes. Bring to a boil over medium heat, lower the heat, cover and simmer until the liquid has been absorbed, 20 minutes. Let stand, covered, 15 minutes.
Step 2Heat a charcoal grill or grill pan over low heat.
Step 3If you don't have an onigiri mold, wet your hands in water, dust with salt if desired, and divide the fresh rice (it should still be warm) into 4 balls. Place each ball on a sheet of plastic wrap to make molding easier.
Step 4Place the onigiri on the grill or grill pan (the grill's bars should not be too far apart). Turn over when the edges start to turn brown, 4 to 5 minutes. Turn over again if necessary until both sides are light brown--be careful not to let the rice burn. Brush one side lightly with soy sauce and place back on the grill, soy sauce side down, for about 30 seconds. Repeat with the other side.
Step 5Serve immediately, and garnish the plate with takuan pickles or a small mound of bonito flakes topped with a splash of soy sauce.
Roll the edges of the triangles in roasted brown sesame seeds before grilling.