Mary Sera, born Mary Akai, is a former MI6 operative and mother to Shuichi Akai, Shukichi Haneda, and Masumi Sera. Though physically regressed to a middle schooler’s form—blonde curls framing piercing blue eyes—her true age remains 53. This transformation stemmed from Vermouth forcibly administering the APTX 4869 during a clash in London, where Mary sought her husband, British intelligence officer Tsutomu Akai, later declared dead. Her lineage ties her to the Miyano family through her late sister Elena, making her aunt to Shiho Miyano (Ai Haibara). Post-regression, she returned to Japan with daughter Masumi, intent on securing an antidote she believes Shinichi Kudo (Conan Edogawa) harbors due to his analogous condition. To this end, she surveils Conan via covert methods like wiretaps, maintaining wary skepticism even as she leverages his insights. A disciplinarian with a tactical mind, Mary enforces a no-nonsense demeanor, once clashing physically with a young Shuichi over rigid expectations. Yet glimpses of warmth surface—pride in Shukichi’s shogi mastery, fierce protection of Masumi during threats. Her MI6-honed instincts drive constant relocations to evade detection, distrust threading every decision. Despite her childlike frame, she disarms adversaries with pinpoint strikes and dismantles surveillance tech with ease, skills echoing her spycraft pedigree. In *The Scarlet Bullet*, she aids FBI and familial allies in probing sports-event-linked kidnappings, deploying her analytical prowess offscreen to navigate the crisis. Her dynamic with Conan balances uneasy alliance against mutual suspicion. To mask their bond, she directs Masumi to label her “the little sister from outside the domain”—a ruse mirroring her broader stratagem of secrecy to shield kin while pursuing a cure. Threaded through her past are the unsolved Haneda Kohji murder and tendrils of the Black Organization’s machinations. Her condition and Miyano ties cement her as a linchpin bridging fractured narratives, her arc entwining with the series’ deepest enigmas.