Amu Hinamori and the Seiyo Elementary Guardians persist in their search for X Eggs to purify them, all while chasing the elusive Embryo—an egg rumored to grant any wish. Yet, the Guardians must secure the Embryo before the nefarious Easter Corporation gets their hands on it. To lure the Embryo out, Easter employs Lulu de Morcerf, a detached girl whose ruby necklace allows her to turn Heart Eggs into Mystery Eggs. These odd Mystery Eggs are harder to purify than X Eggs and can compel their owner to undergo a Character Transformation. Given this rising danger, the Guardians need to find the source and halt the spread before things spiral out of control. Under the heavy strain of these two new goals, can the Guardians retrieve the Embryo while also handling the Mystery Eggs?