A scientist with disheveled hair and poor common sense, a result of her years being a researcher.

In Toaru Kagaku no Railgun, she is revealed to be the creator of the Level Upper, which functions as a network to connect the minds of psychics who use it. This is also revealed to be the source of her powers, because as the administrator of the Level Upper, she is able to access and control the powers of all the psychics linked to the network.

Kiyama's intention is to use the network to save her students, a group of Child Errors that were used in an inhumane experiment that left them in a coma; she has resorted to such extreme measures because the city's administration refuses to allow her to use Tree Diagram to find a cure.
However, when the network goes out of control, it creates a fetus-like creature known as AIM Burst; feeling responsible for creating it, she decide to sacrifice herself to stop it. Uiharu and Mikoto manages to convince her not to for the sake of her students and Mikoto defeats AIM Burst.

After Kiyama is arrested by the Anti-skills, she promises Mikoto to find another way to saved her students but gives Mikoto a hint regarding the existence of the Sisters.

She reappears later in the Railgun anime where she works with Heaven Canceler to find a cure for her students. However, whenever they are close to waking up, their powers overload and cause Poltergeist attacks throughout the city. With the help of Mikoto and her friends, she eventually finds a cure and reawakens her students.

Source:Wikipedia