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 to 4 minutes until onion becomes translucent and tender.
03 - Add chicken pieces to the pan. Cover and simmer for 6 to 8 minutes, turning pieces halfway through, until chicken is fully cooked and no longer pink in the center.
04 - Lightly beat eggs in a bowl. Pour evenly over the chicken and onion mixture. Cover and cook for 1 to 2 minutes until eggs are just set but still slightly runny. Remove from heat immediately to prevent overcooking.
05 - Divide hot rice between two bowls. Gently slide the chicken and egg mixture over the rice. Garnish with sliced spring onions and serve immediately while hot.