Possesses a remarkably mature appearance for Academy City, which is mostly populated by young people. Consequently, her voice actress, Ami Koshimizu, portrays her with the tone of an adult character. However, she was apparently enrolled in high school at least a year ago (based on her "class representative" line in Dark Side Cohabitation Vol. 3), making her likely 18 or 19 years old. (Though Mikoto called her an old lady...) Her personality is self-centered and arrogant. She shows no mercy to enemies and is violent enough to turn on her own allies if her pride or precious things are damaged. However, her "deep affection for comrades" is a double-edged sword that leads to an obsession where "betrayal is absolutely unforgivable"; this, combined with Teitoku Kakine wounding her pride, likely led to her atrocities in Old Testament Vol. 15. According to Rikou Takitsubo, she is "single-minded once she sets her heart on something." She often adds "nyan" to the end of her sentences, but combined with her rough tone, it's more terrifying than cute. Frenda leaked a surprising secret that she "can't sleep without holding a tattered stuffed animal." Incidentally, Mugino is self-conscious about her legs being thick, so she always wears stockings, tights, or knee-high socks to make them look thinner. Her favorite food is salmon bento; she is surprisingly fond of Japanese cuisine. Ability: Meltdowner (Atomic Destruction), Level 5, Ranked 4th.

A member of "Item," one of the organizations operating in the dark side of Academy City. Her catchphrases are "Ultimately..." and "...is the point." She is a high school student who takes pride in the beauty of her legs. Level 0. Her ability is unknown. Her personality is frivolous and optimistic, possessing a nature that takes everything lightly. This is a strength that allows her to enter others' hearts and dispel their worries without hesitation, but it also leads to bad habits like underestimating dark side work (including eliminating targets) and quickly resorting to self-preservation. She also has a sadistic streak, harboring a cruelty where she feels like she controls the opponent's fate the moment she takes their life. She can enjoy watching others kill each other while eating popcorn and watches the rule-free underground "Coliseum" fights live-streamed while having meals in her room.

A member of "Item" who is always seen in a tracksuit. She is a "hidden" busty girl. While organizations formed by ability users often consist of members with cold-blooded ideologies, she is a healing presence in that bleak environment. Her personality is quiet and kind. However, as a member of the dark side, she can hardly be called a "good person," as she does not stop Mugino or Frenda when they massacre or torture targets in front of her. At best, she is loyal and caring toward her comrades; at worst, she is indifferent to herself and others. Shiage Hamazura, who became a handyman for Item, was saved to some extent by her kindness. She entered the dark side because scientists framed her to use her in "Body Crystal" experiments. She was saved by Mugino during that time and has cherished her comrades ever since. According to Kinuhata, she is a high school student. Level 4 ability: AIM Stalker (Ability Tracker).

An ability user belonging to "Item." Level 4 "Offense Armor." She appears to be a quiet girl of about 12 (though she claims to be a middle schooler), wearing a fluffy knit dress. The dress is extremely short, but she calculates the angles so nothing is actually seen. Her verbal tic is adding "super" to everything. Since it's used as a modifier, she can use it multiple times in a single sentence. In her private life, she is a fan of B-movies or lower (and her hobby is collecting used tickets from movies she's seen). Even for R-rated films, she will misrepresent her identity to visit empty theaters. she has specific preferences for how to watch movies but gets bored easily. Her ability is the Level 4 "Offense Armor (Nitrogen Armor)."

A character from "A Certain Magical Index" and one of the protagonists of the series. Level 0. Height is about 175cm. As a Level 0, he has no noteworthy combat abilities, but he primarily fights using weapons. He is skilled at handling guns and cars. Additionally, he cultivated minor technical skills and knowledge such as forging certificates and dismantling ATMs during his time in Skill-Out. He particularly excels at lock-picking, having successfully picked the precision analog lock of a Dragon Rider in one go. Takitsubo tends to be jealous, and Hamazura is dissatisfied when their time together decreases. Despite everything, the two are deeply in love with each other.