Crack the eggs into a bowl. Add the dashi, sugar, and usukuchi shoyu. Mix well with chopsticks — but don't whisk into a foam. You want the eggs blended, not frothy.
Heat a tamagoyaki pan over medium-low heat. Add a thin layer of oil and spread with a paper towel. The pan is ready when a tiny drop of egg sizzles gently — not smoking hot.
Pour a thin layer (about 1/3 of the mixture) into the pan. Tilt to spread evenly. When the surface is just barely set, roll the egg from one side to the other. Push the roll back, oil the empty space, and pour another thin layer — lifting the roll so the new egg flows underneath. Repeat with the remaining egg.
Once all the egg is rolled, press it gently against the side of the pan to shape it into a neat rectangle. Slide onto a plate and let rest for 1–2 minutes. Slice into pieces and serve.
