The Embryo is an egg that can grant any wish, one for each person. The Embryo is a clear white egg with no marks on it. People, such as the evil Easter Company, the Guardians and even the Guardian Characters search for the Embryo. Amu wants to wish that her friends were happy, Rima wants for her family to go back to being a happy family, Tadase for world domination, Yaya to be a baby and to have an all-you-can-eat candy buffet, Ikuto wants the embryo so he can get himself out of Easter, and so on.
The Embryo is the item that motivates the first part of the story, as the Guardians and the Easter Company are out to find the Embryo in order to fulfill their own wishes. In Chapter 41 and Episode 102, the Embryo is revealed to be Hikaru's Heart's Egg. The reason it was never in his heart was because it was driven out by Hikaru, who wanted to stop feeling loneliness. After it was driven out, it began to look for its owner. Thanks to Amu and her Guardian Characters, the egg is able to return to Hikaru. In Chapter 45, Amu's Guardian Characters, Ran, Miki, and Su, disappear from existence. To find them again, Amu goes on a journey with her last Guardian Character, Dia, and Tadase and Kiseki to find the four sparkling shards that will lead her to the Embryo and help her make a wish come true. It is revealed in the last page of Chapter 48 (the final chapter) that the embryo is every single Heart's Egg, meaning Easter's attempts to capture the Embryo were all in vain.
- The Embryo seems to be larger than most eggs.
- It was named after the embryo in an egg, which is the premature animal or plant, as food can have it too.