Pound the chicken to even thickness, about 1–1.5 cm, so it cooks evenly. Season both sides with salt and pepper.
Coat the chicken in flour, dip in beaten egg, then cover with panko. Press gently until fully coated and crumbly.
Heat oil to medium heat (about 170°C). Fry chicken for 6–8 minutes until golden brown and crispy with steady sizzling sounds.
Transfer the fried chicken to a wire rack and let it rest at an angle. This keeps the crust crisp instead of soggy.
In a pan, add dashi, soy sauce, mirin, and sugar. Add sliced onions and simmer until soft and slightly translucent.
Slice the chicken into strips and place it into the simmering sauce. Cook for about 30 seconds so it absorbs flavor.
Lightly beat the eggs and pour over the chicken. Cook for 1–2 minutes until just set but still soft and slightly glossy.
Serve over hot rice and top with green onions. The egg should look soft and slightly jiggly when done.