Rinse the rice in cold water, swirling and draining, until the water runs mostly clear. Cook it in a rice cooker with water to the 1-cup line. On the stovetop, simmer 1 cup rice with 1 cup water, covered, on low for 12 minutes. Then rest it off the heat for 10 minutes.

Cut the chicken into 3/4-inch pieces and trim any excess fat. Whisk the dashi, soy sauce, mirin, and sugar together until the sugar dissolves. Beat the eggs only 4 or 5 times, so you still see streaks of white. That uneven mix gives the topping its classic look.

Pour the sauce into a 10-inch skillet and bring it to a gentle simmer over medium heat. Add the onion and cook for 3 minutes, until it begins to turn translucent. Add the chicken in a single layer and simmer 5 to 6 minutes, turning once, until there is no pink inside. The internal temperature should reach 165°F (74°C).

Reduce the heat to medium-low. Drizzle two-thirds of the egg in a circle over the chicken and cook for 30 to 45 seconds, until the edges look set. Pour in the remaining egg, scatter half the scallions on top, cover, and turn off the heat. Let it sit 45 to 60 seconds. The egg should look glossy and just barely set, because it keeps cooking on the way to the bowl.

Divide the hot rice between two deep bowls, about 1 1/4 cups each. Slide half the topping over each bowl, pouring the extra broth over the rice. Finish with the remaining scallions, nori strips, and a pinch of shichimi togarashi. Serve right away while the egg is soft. Rebecca's Tip: Take the pan off the heat when the egg still looks slightly underdone. Carryover heat finishes it, and overcooked egg turns dry and rubbery. If sodium is a concern, use low-sodium soy sauce and unsalted homemade dashi. You can also fold a handful of baby spinach into the broth with the chicken for extra greens.