Steps

1. Place 1800cc of water and 30g of kombu in a pot and heat. When it reaches 60°C, reduce the heat and maintain for 1 hour. 【This is the key!】 Maintain 60°C for 1 hour to prevent glutamic acid extraction from the slimy part of the kombu.
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2. Remove the kombu after 1 hour.
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3. Raise the pot's temperature to 85°C. Turn off the heat when small bubbles constantly rise from the bottom of the pot.
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4. Add 50g of Bonito Flakes (Katsuobushi) to the pot after turning off the heat and let it sit for 10 seconds.
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5. Strain the Bonito Flakes (Katsuobushi) using a strainer (a double sieve lined with paper towels). 【This is the key!】 Squeeze to remove dashi will make it cloudy, so strain without squeezing.
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6. Cut 70g of chicken thigh into cubes of about 1cm. 【This is the key!】 Since chicken takes time to cook, it's best to cut it as finely as possible. Ensure the pieces are uniform in size to easily mix with the rice and egg.
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7. Slice 10g of green onions into thin strips about 5mm wide. 【This is the key!】 Kujo negi (green onions) wilts quickly when cooked, so cutting them slightly thicker is recommended.
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8. Make the seasoning mixture. Mix 35cc of dashi, 25cc of mirin, and 15cc of usukuchi soy sauce in a bowl.
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9. Pour the seasoning mixture into a small frying pan and heat.
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10. Add the chicken to the frying pan and cook slowly. Simmer until the umami and oil from the chicken are released. 【This is the key!】 Since chicken takes time to cook, check if it's cooked through even if the surface has turned white.
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11. Add a small amount of potato starch mixture made by dissolving 1tsp of potato starch in 1tsp of water. 【This is the key!】 Adding the potato starch mixture thickens the sauce, resulting in fluffy eggs.
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12. Add the green onions and lightly simmer until wilted.
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13. Lightly beat the eggs (do not overmix).
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14. Pour the beaten eggs all at once into the frying pan.
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15. As the eggs begin to set, gently stir them. Turn off the heat when they are half-cooked.
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16. Serve hot rice in a bowl and pour the half-cooked oyakodon topping over the rice.
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17. Sprinkle with sansho powder to taste.
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