Also known as: メアリー世良, 領域外の妹, 赤井メアリー
A character from Meitantei Conan. She is a blonde-haired child staying with Sera Masumi, and acts far wiser than her appearance lets on. She tells Sera that if Conan asks who she is, she should say she is the, "little sister from outside the domain" ("Ryouiki-gai no imouto").
Eventually, she is revealed to be the mother of Sera, Akai Shuuichi and Haneda Shuukichi, de-aged after being forced to take APTX-4869.