Known as Beelzebub or Baby Beel (ベル坊 Beru Bō).
He is the youngest son of the Devil King and is very attached to Oga; always clinging onto Oga's back or sitting on his head.

Beelzebub's characteristic cry is "Daabū!". When he becomes agitated, he'll often throw a tantrum that will spontaneously electrocute anyone within his vicinity. Without Oga, he is physically weaker than even the average human child, however, contact with Oga allows him to unleash his demonic powers. Beel's power increases as he ages and so does Oga's, but the process is accelerated when both undergo training to allow Oga to control his possession by Beel.

Through the series (so far covering a period of about six months), he shows some development, as expected from an infant, and his ability to interact with other people increases. He and Kunieda's little brother Kouta develop a rivalry with comic effect.

Source:Wikipedia

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

A grade school teacher with a rather panicky personality and also a member of the Anti-Skills, where she normally partners with Yomikawa. Her lack of confidence makes her prone to messing up on the field. She enjoys beat-em-up games.

Source:Wikipedia

Tōma's homeroom teacher.

Her house often becomes home to various others. Despite her childish and very short (135 cm) appearance, she is actually an adult whose apartment is littered with beer cans and cigarette packs, though she often contradicts her age by acting childish to her students and ending her sentences with desu, something a child usually does.
This irony means that she is often regarded as one of the seven great mysteries of Academy City.

Ability:
As a teacher, she doesn't have any esper abilities and is capable of assisting in magic spells, assisting Index when healing herself and assisting Stiyl when Aisa gets injured by Oriana.

Source:Wikipedia

Profile:
A Level 4, 2nd year transfer student of Tokiwadai Middle School. She also owns a pet snake named Ekaterina. She originally appears in the eighth novel and makes her first animated appearance in the To Aru Kagaku no Railgun anime, though appears much later on in the manga.

As Kuroko's rival, she is confident, boastful, and desires to become a Level 5. Although she if often boastful about her abilities, she usually finds herself the victim of several attacks. Like all Tokidawai students, she lives in one of the school's dormitories albeit her dormitory is located within the School Garden District.

Ability:
Her ability is called "Aero Hand" (空力使い Kūriki Tsukai, Aerodynamic Touch) which with any object she touches, a powerful gust of wind will take form, propelling it like a missile.
She is able to use multiple outputs to launch heavier objects.

Source:Wikipedia

Profile:
An Amakusa Catholic girl.

Originally introduced in the 11th novel, she makes an earlier appearance in the anime episode "The Book of the Law" which is based on the beginning of the 7th novel.
In the 11th novel, she fell in love with Tōma after their first meeting, claiming it was Love at first sight but the anime suggests she fell for him much earlier during the Orsola incident in the 7th novel.
However due to her shyness, she is unable to properly tell him how she feels. Yet she hopes to get Tōma's attention, even when knowing her senpai and superior Kaori is also in love with him.
She has accompanied Tōma and his friends on more than one occasion, including traveling with him to Italy, France, and Britain. In the events of the 16th novel she becomes his bodyguard and caretaker. When Acqua first attacks Academy City, she fails to protect him and tries to heal Tōma with magic but unsuccessfully due to his Imagine Breaker. After Tōma is sent to the hospital she goes into despair for failing to protect him but Saiji rebukes her and tells her to snap out of it as she focus on fighting with Acqua if she wants to protect him.

During the Amakusas rematch against Acqua, Itsuwa suddenly displays a change of personality, becomes full of tranquil fury that even the way she spoke changed. She performed a "Saint Destroyer" spell in that battle, harming Acqua and causing him to lose the "Divine Mother's Mercy" spell which allows them to defeat him.

Ability:
Her weapon is a Friulian Spear, which by adding layers of reinforcement magic, turns it into a symbol of a 'Thousand Years Tree', which symbolizes the growth of plants and makes certain magic spells to be more potent over time. She also can perform Nanasen (七閃?, "Seven Flash") by manipulating her spear and steel wires just like Kaori.

Source:Wikipedia