Cut the chicken into bite-sized pieces.
Slice the onion thinly.
Beat the eggs in a bowl.
Heat some cooking oil in a pan and stir-fry the chicken.
When the chicken is cooked, add the onion and stir-fry together.
Add soy sauce, sugar, mirin, and water, and bring to a boil.
Once the onion becomes translucent, pour in the beaten eggs.
Cover with a lid and cook until the eggs are softly set.
Spoon the finished mixture over rice to serve.