It is a black boiled egg. Iron sticks to the shell of a raw egg, boiled in the hot springs at eighty degrees Celsius for 1 hour. Then hydrogen sulfide reacts with iron, creating a black coating. Another 15 minutes of steaming, and the egg will be complete. Kurotamago can only be purchased at Kurotamago House. It is said that one egg adds seven years to your life.
by _GrimFandango