Cut off the stems of the shiso leaves, slice them vertically, then chop into thin strips horizontally.

Crack eggs into a bowl, add shiso leaves and seasonings (dashi powder, salt, mirin, water), and mix well by cutting through the egg whites.

Heat a tamagoyaki pan over medium heat, spread salad oil thinly using a paper towel, and pour 1/3 of the egg mixture into the pan. Stir with chopsticks until semi-cooked, then roll the mixture towards you.

Repeat the process: spread oil, pour half of the remaining egg mixture, stir until semi-cooked, and roll towards you. Continue until all egg mixture is used.