Step 1: Prepare the Chicken - Place the chicken breasts between plastic wrap or parchment paper and pound to 1/2 inch thickness.
Step 2: Marinate the Chicken - Mix soy sauce, salt, and pepper; coat chicken and let sit for 15-20 minutes.
Step 3: Set Up the Breading Station - Prepare three shallow bowls with flour, whisked egg, and panko breadcrumbs.
Step 4: Bread the Chicken - Coat chicken in flour, dip in egg, then press into panko breadcrumbs.
Step 5: Fry the Chicken - Heat oil in a frying pan and fry chicken for 4-5 minutes on each side until golden brown.
Step 6: Drain and Serve - Transfer to paper towels, let rest, then slice and serve with katsu sauce.