Cut 285g of boneless skinless chicken thighs into thin bite-size pieces. Toss with 1 tablespoon of sake and leave for 5 minutes.
Mix ½ cup of dashi, 2 tablespoons of soy sauce, 2 tablespoons of mirin, and 2 teaspoons of sugar.
Spread ½ thinly sliced yellow onion in a 10in / 25cm skillet. Add the sauce and bring to a simmer. Add the chicken in one layer.
Simmer uncovered over medium-low heat for about 5 minutes, turning halfway, until the onions soften and the chicken reaches 165°F / 74°C.
Lightly break up 3 large pasteurized eggs with chopsticks, leaving whites and yolks streaky. Drizzle two-thirds over the simmering chicken. Once starting to set, add the rest and 4 chopped sprigs of mitsuba. Cook until the whites set; cover briefly if needed.
Spoon the chicken and egg, with the pan sauce, over 500g of hot cooked Japanese short-grain rice.
