Place in a frying pan:
2 T soy sauce
2 T mirin
1 T sake
2 t sugar
1 medium onion, sliced into thin wedges
Boil until onions are soft, about 2 minutes.
*(If you happen to use chicken breast instead of thigh, slice it thinly against the grain. It cooks more quickly than chicken thighs.)
Simmer for 2-3 minutes.
Scramble in a bowl:
Pour 2/3 of the eggs over the chicken. Cover and simmer for 1-2 minutes. Add the remaining egg. Cover and simmer for 10 seconds or until the egg is set to your liking.
Serve over rice. (Sprinkle with sesame seeds.)