Yanagisako Aomi

A friend, roommate, classmate, and fellow Judgment member of Konori Mii in Toaru Kagaku no Railgun.

Background
She knows a lot of details regarding Mii, including her ordeal with a robbery which put a younger Shirai Kuroko, then a trainee of Judgment, in a battle with a high-level Power User, and her days as a member of Big Spider, then led by Kurozuma Wataru.