The story centers on elementary schoolgirl Amu Hinamori, whose popular exterior, referred to as "cool and spicy" by her classmates, contrasts with her introverted personality.
When Amu wishes for the courage to be reborn as her would-be self, she is surprised to find three colorful eggs the next morning, which hatch into three Guardian Characters: Ran, Miki, and Su.
Like Jun Sakurada in Peach-Pit's previous work, Rozen Maiden, Amu tackles issues such as alienation and fitting in at school.
Unlike most heroines in other magical girl series, Amu is neither the perfect sweetheart nor a complete klutz.
Amu gets grumpy and frequently talks back to others in contrast to the polite schoolgirls that fill the genre.
Eventually, Nadeshiko Fujisaki and Kukai Soma leave the Guardians and are replaced by Rima Mashiro and Kairi Sanjo, respectively.
She can be identified as a tsundere (cold and mean to opening up to other people), but her true character is shy and timid.
Part of the reason for this misunderstanding is the trendy punk goth clothing her mother buys for her as well as the way she expresses her shyness.
In the second season, when Amu shows her true potential, the Humpty Lock increases in power.
She initially regarded Ikuto as a jerk and pervert, but she grew close to him as he aided her countless times.
When Tadase asks Amu if it is okay for him to fall in love with her, she is thrilled at the progress in their relationship but soon finds herself drawn to Ikuto.
After he confesses to her and kisses her close to the lips, she refuses to admit her feelings for him, which prompts Ikuto to make a deal with her that he will get her to fall in love with him.
In the final chapter of Shugo Chara Encore, she is happy to reunite with him and is seen holding hands with him at Sanjou and Nikaidou's wedding.
In some of the later chapters, when Amu opens the Humpty Lock with the Dumpty Key, she and Tadase see more of Ikuto's past.
Their journey ends when the Amu Character transforms with Diamond, and she and Ikuto fight briefly.
Amu ventures to the Eggs' Cradle, a place where unborn and "lost" Shugo Chara reside, to search for four coloured shards representing each of her Shugo Chara in an attempt to bring Ran, Miki and Su back.
She finally comes to terms with the loss of her Guardian Characters at the end of the journey, however as she returns she realizes that she has Ran, Miki, Su and Diamond back in Egg form much to her relief and later joy as they are reborn later in Shugo Chara!
Tadase ventures into the Eggs' Cradle with Amu, but subsequently gets separated from her because of a meteor shower.
Ikuto actually despises Easter and tries to wrench himself free from them by trying to find the Embryo to grant that wish.
As the series goes on, he grows very strong feelings for Amu—he confessed that he loves her in the same chapter Tadase does, although she believes he is teasing her.
In the manga timeline, it is shown he character transforms with a new black Guardian Egg to become Death Rebel, shocking Amu.
In one of the later chapters, Ikuto calls Amu "princess" and she replies by asking him to thank her for making him get back to normal.
She was the vocalist of the indie band Black Diamond which is produced by her manager, Yukari Sanjo.