Ayumi Yoshida is a student in Teitan Elementary School when Shinichi joins her class as Conan Edogawa. Ayumi befriends Conan and convinces him to join her, Genta, and Mitsuhiko in investigating an apparently haunted mansion. As it turns out, the haunting is a cover-up for an old homicide case, and due to Conan, the mystery is solved and the culprits are arrested.

Soon after, the accidental acquisition of a treasure map leads Ayumi, Genta, Mistuhiko and Conan on a hunt for a cache of stolen Italian gold coins, during which Conan saves them from getting killed by the mafia members who are also after the gold. His actions earn Ayumi's gratitude, which quickly develops into a serious crush. Additionally, after the case is resolved, Ayumi joins Genta and Mitsuhiko in forming the nucleus of an amateur detective group, the Detective Boys. Ayumi is the sole female member of the Detective Boys until Ai Haibara joins their ranks.

Ayumi is a primarily naive and innocent little girl who enjoys adventure. She demonstrates courage as time goes on and acts as the group's cheerful spirit. She has an open crush on Conan, even dreaming about marrying him, which makes him uncomfortable. At the same time, Ayumi thinks that he has feelings for Haibara because he tries to protect her and she often sees them talking amongst themselves in private. Ayumi later becomes better friends with Haibara and she allows Ayumi permission to use the more informal term Ai-chan to address her.

When on a case, Ayumi often makes simple observations that help lead to progress and resolution. For instance, she unlocked one of the codes from the Momotaro container the Detective Boys found in Kurashiki by deducing that it was most likely referring to one of the statues at the Oohara Art Museum: they had to walk 25 steps from the statue towards the direction it was facing. She has an eye for noticing strange details in people's appearance, like she noticed that Taiko Mejin was shaved while dressed casually, while he normally made it grow when he is not wearing a kimono.

(Source: Detective Conan World)