Crack eggs into a medium-sized bowl and whisk with chopsticks until fully combined.
Mix together Dashi, soy sauce, sugar, and mirin in a separate bowl.
Add seasoning mixture to eggs and gently whisk.
Cooking the Omelette
Heat nonstick pan over medium heat. Once hot, spray cooking oil to cover all sides and edges.
Pour a thin layer of the egg mixture into the pan until the surface is fully covered.
Once the bottom side of the first egg layer has set, gently roll the egg towards you, and press out any air bubbles.
Spray another layer of cooking oil, then add a second layer of the egg mixture to the pan. Be sure to lift up the previously rolled layer to add egg underneath.
Once the new layer has set, repeat rolling the omelette, and press out excess air.
Repeat steps until all the egg mixture has been used. If desired, allow to cool in a sushi mat or layer of plastic wrap to set shape.