Cook 2 cups of white rice according to package directions or in a rice cooker. Set aside and keep warm.

Cut 500g chicken thighs into bite-sized pieces, about 1-inch cubes.

Slice 1 medium onion into thin half-moon slices.

In a measuring cup, combine 200ml water, 3 tablespoons soy sauce, 3 tablespoons mirin, 2 tablespoons sugar, and stir until sugar dissolves to make the sauce.

Heat a large skillet or shallow pan over medium-high heat. Add 1 tablespoon vegetable oil.

Add the sliced onions and sauté for 2-3 minutes until they begin to soften.

Add the chicken pieces to the pan and cook for 4-5 minutes, stirring occasionally, until the chicken is mostly cooked through.

Pour the prepared sauce over the chicken and onions. Bring to a simmer and cook for 5 minutes, allowing the sauce to reduce slightly.

While the chicken simmers, beat 4 eggs in a bowl with a fork until well combined but not frothy.

Reduce heat to medium-low. Pour the beaten eggs evenly over the chicken mixture in a circular motion.

Cover the pan with a lid and cook for 2-3 minutes until the eggs are just set but still slightly runny on top.

Remove from heat immediately to prevent overcooking the eggs.

Divide the hot cooked rice among 4 bowls.

Carefully spoon the chicken and egg mixture over each bowl of rice, ensuring each portion gets both chicken and egg.

Garnish with thinly sliced green onions and serve immediately while hot.