In a medium bowl, combine the dashi, soy sauce, and sugar, stir until the sugar dissolves. Add the eggs to the bowl and mix (don't over whisk) to combine. Strain the egg mixture using a medium-mesh sieve over a measuring cup with a spout. Stir and move the eggs with a spoon to get most of the liquid through, a small amount of the thick whites may remain in the sieve.
Use a rectangular tamagoyaki pan called a makiyakinabe or tamagoyakiki to make this rolled egg dish. If you don't have one, a regular pan will do. Oil the pan before cooking, to prevent sticking. Using a paper towel or reusable equivalent, wipe the sides of the pan with oil to make sure the eggs don't stick to the sides.
Heat the frying pan over medium heat.
Pour a thin layer of the egg mixture into the square frying pan, when it starts to set, roll and add a new layer. A Japanese cook would roll the eggs up using chopsticks, however, you can use a spatula or whatever you feel comfortable with to get the job done.
Cook and roll one thin layer of the egg after another until the mixture is used up. Depending on the size of your pan and how many eggs you use, this process may be repeated multiple times.
Roll the egg mixture and leave it to rest, then slice and serve; either in Nigiri or Sushi recipe, or just add to a Bento box!