Summary
Diamond, whose true identity remains a mystery, serves as Amu’s fourth Guardian Character and brings a distinct musical element to the group. Initially turning into an X Egg due to Amu’s resistance to change, she hatches as an X Character after Utau discovers the egg, undergoing a character transformation into Dark Jewel alongside her. Since Amu was unaware of her actual name, she simply refers to the Guardian as "Dia," a nickname derived from "Diamond." Once Amu convinces Dia that she is capable of change, the X-mark vanishes, triggering a Character Transformation that merges them into Amulet Diamond. Dia originally disliked Amu for lacking a sparkling heart like Utau, but after realizing Amu possesses one, she returns to her side. Following this reconciliation, Dia retreats into her egg to slumber until Amu shines once more, though she occasionally emerges in select episodes.
