Season the chicken tenders with salt and pepper, to taste, and set out the flour, 1 egg, and panko breadcrumbs in 3 separate small bowls. Heat ½ inch of oil in a frying pan until a frying thermometer reads 350 degrees.
Dredge the chicken in the flour, egg, then panko breadcrumbs, and deep-fry until golden brown. Drain on paper towels.
Make 2/3 cup dashi stock according to package directions. In a frying pan, combine the onion, dashi stock, sake, mirin, soy sauce, and sugar to a boil. Reduce the heat to medium and cook the onion until wilted. Add the chicken katsu and increase the heat medium-high. Pour and distribute the remaining egg evenly.
When the eggs are halfway cooked, add the mitsuba and turn off the heat. Serve the rice in a bowl and put the chicken and egg mixture on top. Serve with ichimi togarashi on the side.