Amu Hinamori is a shy girl who struggles to make friends, partly due to rumors circulating at school about her "cool and spicy" personality. Hoping to show everyone her "would-be" self, Amu wakes up to find three colorful, ornately decorated eggs in her bed. Each of these "Hearts Eggs" houses a "Guardian Character"—manifestations of a person's would-be self and their dreams. With the help of Ran, Miki, and Su, Amu becomes able to express who she truly is. However, things do not always go in her favor. The sudden appearance of Amu's Guardian Characters draws the attention of the Seiyo Elementary Guardians, a student council-like group whose members each possess their own Guardian Character. Because she has multiple Characters, Amu is recruited as the Guardians' "Joker," tasked with helping them find X Eggs—corrupted versions of Hearts Eggs. As she becomes entangled in the Guardians' quest, Amu begins to uncover more about these mysterious Characters, the X Eggs, and the organization that appears to be at the center of it all.