01 - Combine dashi stock, soy sauce, mirin, sake, and sugar in a small bowl. Stir 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 tender and translucent.
03 - Add chicken pieces to the pan. Cover and simmer for 6–8 minutes, turning halfway through, until chicken is fully cooked and no longer pink inside.
04 - Lightly beat eggs in a bowl. Pour evenly over 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 rice between two serving bowls. Gently slide the chicken and egg mixture over the rice, maintaining the layered presentation.
06 - Top with sliced spring onions. Serve immediately while eggs remain silky and warm.