The Missing Page
The Heart's Egg (Kokoro no Tamago) is an artbook created by the Founding King of the Guardians. It contains information about Heart's Eggs and Guardian Characters. Some pages are lost for unknown reasons, the missing pages may mean what's next will be up to the child to create their own future.
Every child has a egg within their soul.
This heart's egg can't be seen with one's eye.
But, as the child grows up it disappears...