01 - Combine dashi stock, soy sauce, mirin, sake, and sugar in a small bowl. Stir thoroughly until sugar completely dissolves.
02 - Heat a medium skillet over medium heat. Add sliced onion and sauce mixture. Simmer for 3-4 minutes until onion becomes translucent and softened.
03 - Add chicken pieces to the pan. Cover and simmer for 6-8 minutes, turning pieces halfway through, until chicken is fully cooked and no longer pink inside.
04 - Pour beaten eggs evenly over the chicken and onion mixture. Cover and cook for 1-2 minutes until eggs are just set but still slightly runny. Remove from heat immediately to prevent overcooking.
05 - Divide hot steaming rice between two serving bowls. Gently slide the chicken and egg mixture over the rice, distributing evenly between bowls.
06 - Sprinkle sliced spring onions over the top. Serve immediately while eggs remain silky and warm.