Rinse 2 cups of Japanese short-grain rice under cold water until the water runs clear. Place in a rice cooker with 2 cups of water and cook according to the manufacturer's instructions.

Once cooked, let it steam for an additional 10 minutes.

In a medium-sized bowl, combine 2 tablespoons of miso paste, 1 tablespoon of mirin, 1 teaspoon of sake, 1 teaspoon of sugar, and 1 tablespoon of butter. Mix until smooth.

Once the rice has cooled slightly, divide into 6 equal portions and shape into triangles using cling wrap.

Heat a non-stick skillet and melt 1 tablespoon of butter. Grill the miso-flavored rice balls for about 1 minute on each side, brushing with the miso mixture.

For the soy sauce variation, use 1 tablespoon of vegetable oil and grill the rice balls for 1 minute on each side, basting with soy sauce.

Transfer to a plate, top with butter, garnish with chives and sesame seeds, and serve warm.