What kind of person will I become? What can I do for myself? Children ponder those very questions, and from those thoughts, the "Heart's Egg" is born. Unseen by most, the Heart's Egg remains hidden within every individual, and represents a person's own ideal character.

While adjusting to life at a new school, Amu Hinamori has unintentionally gained a reputation for being "cool and spicy." Unhappy with her outward persona, Amu often wonders how she can act more like her true self. Her desire for change is manifested when one morning, Amu awakens to find three eggs beneath her. They hatch to reveal Ran, Miki and Suu—three "Guardian Characters," each an embodiment of Amu's ideal self.

Shugo Chara! follows Amu's journey as the trio begin to show her just how much potential she has, encountering other Guardian Characters, and a few troublesome experiences along the way.