Boil water in a pot, add chicken breast, and simmer on low heat for about 10 minutes until cooked. Remove and let cool.

Gently place the egg into the same pot using a ladle and boil for 10 minutes. Cool in water and peel the shell to make a boiled egg.

Chop the pickled radish into small pieces.

Mash the boiled egg in a bowl using a fork. Add sugar, salt and pepper, vinegar, mayonnaise, pickled radish, and chopped green onion. Mix well to create the tartare sauce.