Rinse 1 cup Japanese short-grain rice under cold water until the runoff is clear. Drain well.

Transfer rice to a rice cooker with 1¼ cups water. Cook until tender (about 30 minutes), then rest covered for 10 minutes.

In a mixing bowl, whisk 4 large eggs with 1 tbsp sugar, 1 tsp soy sauce, 1 tbsp mirin, and optional 1 tbsp dashi until smooth.

Heat a nonstick pan over medium-low and brush with oil. Pour in a thin egg layer, cook until edges set (2-3 minutes), then gently roll and push aside.

Transfer the rolled tamago to a cutting board, let it rest for a minute, then slice into ½-inch pieces.

Divide steaming rice between two bowls, top with sliced tamago, drizzle soy sauce or tamari, and sprinkle garnishes.