Shirai's friend and colleague in Judgment and another protagonist in Toaru Kagaku no Railgun. Shy and humble, she goes to Sakugawa Junior High, different from Shirai's, and is known for wearing a headband made of flowers on her head, and sometimes a surgical mask as she constantly suffers the flu. She has a sweet tooth but is often called for Judgment duties before she can enjoy her sweets. She displays various skills with the use of the computer, such as repelling hackers and information gathering.
She makes a cameo appearance in the opening of the Index anime and appears as a supporting character in the second season. She has small parts in the novels, larger ones in the Railgun SS novels.