Atsuko Tanaka
is a middle-school age girl with light hair who has been hiding in various hotels in Tokyo with Masumi Sera. Despite her appearance, she is actually a middle-aged woman and the mother of Shuichi Akai, Shukichi Haneda and Masumi Sera. She is an MI6 agent. During the timeline of "Holmes' Revelation", Vermouth fed Mary something like APTX 4869, which caused her body to shrink from that of a middle-aged woman to that of a middle-school child, on the Vauxhall Bridge. Vermouth also implied that Elena Miyano is the younger sister of Mary after feeding Mary the drug. Her eyes have a remarkable resemblance to those of Shuichi Akai and Masumi Sera. She is voiced by Atsuko Tanaka.