Mary

Mary is cautious, intelligent, stern, and highly suspicious of unfamiliar people. She prefers gathering information before making contact and repeatedly instructs Masumi to test Conan rather than immediately revealing everything they know.

Her demeanor is markedly adult despite her small body. Mary speaks with confidence, analyzes threats quickly, and displays the discipline expected of someone accustomed to intelligence work.

She is also fiercely protective of her family. Much of her secrecy is motivated by the danger surrounding them, and she remains willing to take significant risks when information about her husband, children, or the Black Organization is involved.

Mary possesses strong deductive and observational abilities together with the training of a British intelligence operative. She can analyze dangerous situations rapidly and displays considerable knowledge of surveillance, concealment, and counterintelligence.

Despite her reduced body, she retains impressive physical ability. Her reflexes and combat instincts surprise Conan, who quickly realizes that her apparent age gives a misleading impression of her capabilities.

Mary's current body is the result of APTX 4869. Like Shinichi Kudo and Shiho Miyano, she survived the drug and physically regressed rather than dying. Unlike Conan, however, she suffers recurring weakness and coughing associated with her condition.

Mary first appears indirectly while Masumi is staying in hotels and behaving secretively around Conan. Conan glimpses the mysterious girl and begins trying to determine who she is and why Masumi is hiding her.

Mary simultaneously investigates Conan. His intelligence, unusual behavior, and apparent connection to temporary bodily restoration convince her that he may possess information relevant to her own condition.

Mary is actually an adult MI6 agent and the mother of Shuichi Akai, Shukichi Haneda, and Masumi Sera. She is also the older sister of Elena Miyano, making Shiho Miyano and Akemi Miyano her nieces.

While investigating the disappearance of her husband Tsutomu, Mary is confronted in London by Vermouth, who forces APTX 4869 into her mouth. Mary escapes by jumping into the Thames and subsequently discovers that the drug has reduced her body. Her return to Japan with Masumi is partly motivated by the possibility that Conan has access to an antidote.

Masumi Sera travels with Mary and protects her identity while the two move between hotels. Masumi is Mary's daughter and acts as her principal intermediary while Mary remains hidden.

Shuichi Akai is deeply connected to Mary's past. He is her eldest son, whose decision to join the FBI initially causes tension because Mary understands the dangers surrounding the investigation of his father's disappearance.

Shukichi Haneda is another member of Mary's hidden family. He is her second son and was later adopted into the Haneda family.

Tsutomu Akai is central to Mary's involvement in the long-running mystery surrounding the Akai family. He is her husband, whose disappearance while investigating Kohji Haneda's murder leaves Mary searching for answers.

Elena Miyano has a concealed familial connection to Mary. Elena is Mary's younger sister.

Ai Haibara is connected to Mary through that same family history. Haibara is Shiho Miyano, Elena's daughter and therefore Mary's niece.

Conan Edogawa becomes the subject of Mary's investigation because she suspects he possesses information about reversing her condition.

Vermouth is connected directly to Mary's transformation. Vermouth disguises herself during their confrontation in London and forces Mary to swallow APTX 4869, causing her physical regression.