A Guardian Character with an artistic flair, Miki is cool and quiet. She sports a short bob cut and usually dresses in half-cut pants, a sky blue beret adorned with a spade, and a blue-themed outfit. Miki has shown interest in both Kiseki, Tadase's Character, and Yoru, Ikuto's Character. She finds Yoru cool and thinks his tail is cute, which may reflect Amu's feelings.
In the anime, Miki also expresses fondness for Musashi, Kairi's Chara, although Amu does not have romantic feelings for Kairi, who has a crush on her. The main ability after Character Change with Miki is an enhanced artistic sense, though this power can be recklessly abused.
Amu transforms into "Amulet Spade" when she Character Transforms with Miki. The clover decoration on her Humpty Lock changes to blue. Her outfit consists of a white frilly blouse, light blue pants, long striped stockings, and a garter belt, all in a blue theme. Her special move is "Colorful Canvas," where she wields a giant paintbrush to paint. During the transformation, Miki says, "Drew, Draw, Drawn."
When first introduced, Miki witnessed Amu yelling at Ran, the first hatched Guardian, to leave her life. Scared by Amu's outburst, Miki ran away but was later discovered as Amu's spade guardian. Miki is shy yet outgoing, embodying a unique mix of traits.
