Isobeyaki

Combine koikuchi soy sauce, mirin, and granulated sugar in a small saucepan. Heat over low flame, stirring until the granulated sugar dissolves and the mixture slightly thickens, forming a glaze. Set aside.

Preheat a grill pan or toaster oven to medium-high heat.

Place the mochi cakes on the preheated grill pan or toaster oven. Grill or toast for 5-7 minutes, turning occasionally, until the mochi softens and puffs up, and the surface is lightly golden and crispy.