Who may be the sister outside the realm in Detective Conan?

The sister outside the realm is one of the characters in "Detective Conan". Her true identity is Akai Marie. Her true identity was revealed in episode 759 of the TV series.

Akai Marie’s introduction:

Akai Marie, British, Japanese-English mixed race, about 53 years old, her true identity is an agent of the British Army Intelligence Bureau Six (MI6). A long time ago, Belmod took the experimental drug APTX-4869, which caused his body to accidentally shrink into the appearance of a junior high school student. He is currently about 13 years old. She lives with Masumi Sera in a hotel in Tokyo, Japan, but often changes places.

Akai Marie is the mother of Akai Shuichi, Haneda Hideyoshi and Sera Masumi, and the sister of Miyano Arena. She has a deep relationship with the black organization, and it is even speculated that she may be an undercover agent who once lurked in the black organization.