Prepare the Pan: In a small, individual-sized skillet (an Oyakodon pan is perfect), combine the dashi stock, soy sauce, mirin, and sugar. Add the thinly sliced onions in an even layer. Bring the mixture to a simmer over medium heat.

Simmer the Chicken: Once the onions soften slightly, arrange the bite-sized chicken pieces in a single layer over the onions in the bubbling sweet-savory broth. Cook for 3 to 4 minutes, flipping the chicken pieces once, until they are entirely cooked through.

Add the Eggs (The First Pour): Take the lightly beaten eggs (do not over-beat them; you want distinct streaks of white and yellow). Drizzle exactly two-thirds of the egg mixture evenly over the simmering chicken and onions. Do not stir! Cover the pan and let it cook for 30 seconds until the egg is mostly set.

Add the Rest (The Second Pour): Remove the lid. Drizzle the remaining one-third of the egg mixture into the pan. Cover immediately, turn off the heat completely, and let the residual heat steam the eggs for 30 seconds. The top layer of egg MUST remain soft and slightly runny!

Serve: Quickly slide the entire weeping, savory chicken-and-egg mixture directly from the skillet over the top of a deep bowl of hot, steamed white rice. Garnish with chopped green onions or Mitsuba.