Ayumi is introduced into the series after Conan Edogawa joins her class. Soon after, she, along with Conan Edogawa, George Kaminski/Genta Kojima, and Mitch Tennison/Mitsuhiko Tsuburaya, form a group they name the "Junior Detective League," or "Detective Boys" (Shounen Tanteidan) in the original version. Much to the dismay of Genta and Mitsuhiko, Ayumi has a crush on Conan. In the fifth movie, she openly tells Ran of her love for him.
Ayumi has a personality much like any other normal schoolgirl, and is obsessed with popular trends in her school as Masked Yaiba and Japanese monster films. While being quite naive, she is very dedicated to her friends. Her cheerful personality and her courage to meet danger in spite of her own fears have supported the "Junior Detective League" - especially Ai - on more than one occasion.
Starting in volume 39 of the manga, Ayumi becomes the only one of the children who uses Ai Haibara's first name, calling her "Ai-chan" in the Japanese version. Mitsuhiko and Genta call her "Haibara-san", while Conan simply calls her "Haibara."