A Guardian Character with an artistic flair. A cool, quiet character. Her hairstyle is a short bob cut. She usually wears a pair of half-cut pants, a sky blue beret with a spade on it, and a blue themed outfit. Miki has shown an interest in both Tadase's Character, Kiseki, and Ikuto's Character, Yoru. She comments that Yoru is cool and his tail is cute. This may imply the situation in Amu's heart.  

In the anime, she is also shown to like Musashi, Kairi's Chara. Though Amu doesn't love Kairi herself, he does have a crush on her.  

The main ability after Character Change is an increased artistic sense but that power is recklessly abused.  

Amu becomes "Amulet Spade" when she Character Transforms with Miki. The clover decoration of her Humpty Lock changes to the color blue. Amu wears a white frilly blouse with a pair of light blue pants. She also wears long, striped stockings and a garter belt; all in a blue themed costume. Her special move is "Colorful Canvas", where she paints with a giant paintbrush. Miki says "Drew, Draw, Drawn" during a Character Transformation with Amu.   

When first introduced, Miki saw that Amu was yelling at Ran (First hatched Guardian) so that she could leave her life. Miki ran away being scared by Amus outburst.Miki was later found out to be Amus spade guardian. Miki is shy, yet also out-going at the same time. 

Amu Hinamori is a 5th grade transfer student who is fashionably cool, tough and independent. Despite this, she is also a girl who seems unapproachable, both at home and at school. In reality, the "Cool and Spicy" role she plays is just a facade that she unconsciously plays. With her guardian characters, she fights the Easter Company who is extracting people's eggs to create X Eggs & X Characters in search of a special egg called the Embryo.
 
(Source: Crunchyroll)

Amu meets a super-peppy transfer student at Seiyo Academy Elementary School named Hiiragi Rikka at school one day. Not only can she see Guardian Characters, but it seems she has some other, mysterious powers as well. When she sees the work that Amu and the other Guardians do at school, she's awestruck. 
Each 24-25 minute episode consists of a series of variety show style shorts (including Shugo Chara! Pucchi Puchi) totaling approx. 9-10 minutes, followed by the main 11-12 minute animation titled Shugo Chara!!! Dokki Doki which is the actual continuation of season 2 and comes with it's own opening animation. The remaining time is occupied by live action padding between each section and capped off with the opening/ending themes at the beginning and end of the episode. 
(Source: AniDB)

With things having quieted down a bit for the Guardians, they can now focus on things besides fending off the peril of the evil Easter Corporation. Amu is having some troubles deciding which guy she likes the most, and hiding Ikuto in her room. Not only does the Embryo still elude the Guardians, and worries of Easter being suspiciously inactive, the threat of a new X Egg appears...

Everybody at Seiyo Elementary thinks that stylish and super cool Amu has it all: But nobody knows the real Amu, a shy girl who wishes she had the courage to truly be herself. Changing Amu&rsquo;s life is going to take more than wishes and dreams&ndash;it&rsquo;s going to take a little magic! One morning, Amu finds a surprise in her bed: three strange little eggs. Each egg contains a Guardian Character, an angel-like being who can give her the power to be someone new. With the help of her Guardian Characters, Amu is about to discover that her true self is even more amazing than she ever dreamed. 
(Source: Del Rey) 
Note: Includes 3 side stories.

Amu's beloved Guardians Characters finally nab the spotlight in this new Shugo Chara series! Ran, Miki, and Su explore holidays, exercise, bears, cooking, painting, and more character changes than you can count in these hilarious and lighthearted short stories, told in 4-koma (4-panel) comic-strip format.
 (Source: Kodansha USA)

After graduating from Seiya Elementary School, Amu is ready to start junior high school. Amu is glad to be with her dear friends, but then she is asked to undertake a "secret mission" and has to transfer to a new school…?　A new adventure of Amu and Shugo Chara is about to begin! 
 
(Source: Comic Days, translated)