Amu's innocent and pure-hearted three-year-old sister with the ability to see Guardian Characters despite the fact that she does not have one. In chapter 4 of the manga, Ami thinks that Amu's Guardian Characters are dolls, so Amu left her Guardian Characters with Ami so Amu could deliver sweets to Tadase, only to soon find out that she delivered the wrong one. In the Japanese version of the manga, Ami merely said shugoi, and the Guardian Characters thought she was mispronouncing "Shugo Chara". Unlike Amu, Ami is dressed in "Girly Lolita" clothing. She respects and looks up to both Utau and Amu. She loves to sing.

It is Ami that turned Utau into the light. In chapter 25, Ami was lost while trying to go home. Nagihiko then brought her to where the Guardians and Utau where fighting. When Ami arrived, she hugged Utau, and while Amu was holding Ami back, Amu explained that Ami always watches Utau on TV and idolized her. Ami told her to sing and Utau realized that she, when young, was just like Ami and wanted to sing to make people happy, not take away their hopes and dreams. Ami was used as a plot device in chapter 26.