Add 3 tablespoons of mirin.
Cut the chicken into bite-sized pieces.
Slice the onion thinly.
Beat the eggs well.
In a pan, bring soy sauce, mirin, sugar, and water to a boil.
Add the onion and chicken to the sauce and cook until done.
Once the chicken is cooked, pour the beaten eggs over, cover, and cook until the eggs are softly set.
Serve over rice.