Beat the eggs, and divide into 2 portions (one portion should have slightly less than the other).
Add ketchup to the lesser portion, and soy sauce and mirin (or sugar) to the other.
[First Roll] Pour the ketchup egg mixture into the pan, spread it all over, and cook. Roll up from the farthest end, wrapping the roll to the other end of the pan. *Avoid browning for a beautiful finish.
[Second Roll] Pour the other egg mixture into the pan, spread it all over, and roll the cooked ketchup layer up inside it.
Cut into 4 (or how many pieces you like).
Flip one half over, put the centers together to form a heart, and it's done.
You could form the tamagoyaki into a four-leaf clover and stuff it in your bento.
You could add more ketchup for a brighter pink color, but the egg mixture will become soggy and hard to form, so I suggest 1 teaspoon for a pastel pink hue.
The tamagoyaki in most of the pictures were made with 1 teaspoon of ketchup, but the profile photo and Step 8 was with 2 teaspoons (and it was difficult to roll).
Story Behind this Recipe
I remembered that when I was young, I saw this tamagoyaki recipe on a kids' cooking show and often used to make it.
Pack this in your bento for cherry-blossom viewing, in charaben, or when you are making bento for someone dear to you.
The ketchup colors the egg a deep red at first, but when heat is added it'll become pink, so don't worry! Make sure to grease the pan well to prevent sticking! Prevent the egg mixture from browning by cooking over a low heat. This will ensure that the cute pink color doesn't turn brown. Even if it does brown on the exterior, the inside will still have a pink color and be cute.