Amu Hinamori and the Seiyo Elementary Guardians keep pursuing their mission to locate and cleanse X Eggs while chasing the elusive Embryo—a legendary egg rumored to grant any wish. Yet they must claim the Embryo before it slips into the clutches of the sinister Easter Corporation. To bait out the Embryo, Easter employs Lulu de Morcerf, a distant girl whose ruby pendant lets her transform Heart Eggs into Mystery Eggs. The new Mystery Eggs are not only difficult to purify but also carry a latent power that can force their bearer into an involuntary Character Transformation. With this escalating danger looming, the Guardians must uncover the source of these eggs and halt their spread before chaos ensues. Facing overwhelming pressure from these twin objectives, can the Guardians retrieve the Embryo while also confronting the Mystery Eggs and protecting their school from the looming threat? Their investigation takes them into the heart of their city, where secrets await.