In a medium bowl, add all the ingredients (eggs, soy sauce, sugar, dashi powder, water, mirin). Mix everything, but try not to overbeat the eggs.
Add vegetable oil in a square pan. Turn the heat to medium. When the square pan gets hot enough, add 1/3 beaten egg in the pan. Stir with chopsticks in a circle a couple of times.
While the egg is still not cooked, roll the egg toward you to collect on one side.
When the bottom is cooked enough to flip, flip the eggs over.
Add another egg(1/3) where there is no egg in the pan. Gradually roll the cooked egg from the first part until the last layer is covered and you have a neat roll.
Add the last egg(1/3) where there is no egg in the pan. Gradually roll the cooked egg from the first part until the last layer is covered and you have a neat roll.
Lastly, push the egg against the edge of the pan to shape it.