Headband Girl

The Headband Girl (カチューシャ子) is an unnamed recurring background character in Toaru Majutsu no Index. Originally an exclusive character to the novels, she later appears in both the manga and anime adaptations of the series. She acts as an Easter egg in the series and generally appears in illustrations where Kamijou Touma's class from A Certain High School is involved alongside the Spiky-haired glasses girl who is apparently her friend, at least in the anime and manga adaptations.

She is referred to by Haimura as the Background Girl (モブ子), "" referring to a minor character in a video game.

Appearance
In the original light novels, she is a brunette with short hair that never reaches the shoulders like bowl cut. Her most prominent feature is her headband tucked over several of her fringes. Her appearance in the manga is retained. However, in the anime adaptation, her hair becomes thicker and longer.

Kazakiri Hyouka Arc
In her debut, she is featured in the colored illustration of the scene where Index first appears in Touma's class. She sits in front of Touma in the illustration next to wall adjacent to the halls.

In the manga adaptation, she first appears alongside the glasses girl as Touma checks the classroom to see if his class would notice he has lost his memories.

Daihasei Festival Arc
She appears in the background in one of the colored illustrations depicting the scene where Touma accidentally drenches Fukiyose Seiri with water.

In the anime adaptation, she is part of the group of classmates that Touma rouses to defeat a more powerful rivaling school whose teacher insulted Tsukuyomi Komoe, and is later successful in defeating them.

Skill-Out Uprising
She is present in both the colored novel illustration and the anime as part of the class in their organized eat out in a sukiyaki shop.

Acqua of the Back Arc
She is in the colored illustration depicting where Index, Misaka Mikoto, and Itsuwa meet each other in the public bath in School District 22.

Ichihanaran Festival Arc
She appears in the front cover of the 5th Shinyaku Toaru Majutsu no Index novel alongside Thor and Touma, apparently busy with Ichihanaransai, making her the only unnamed character to be featured in a cover.

Magic God Othinus Arc
She appears in the background alongside Himegami Aisa on one of the colored page spreads of the 9th Shinyaku Toaru Majutsu no Index novel, depicting the Version_Beta world Othinus creates to break Touma's spirit.

St. Germain Arc
She appears in the illustrations where ITEM is seen waiting in the mid-level of Dianoid for Hamazura Shiage in the background, alongside one of the St. Germains. She is shown wearing a waiter uniform, apparently working in a restaurant.

Magic God Invasion Arc
Headband girl's existence is mentioned for the first time by the High Priest to Kamijou Touma. He notes how often she blends in the background like she belongs despite Touma not knowing who she is. He refers to her as the Observer, the evidence High Priest gives that Touma is an incredibly extraordinary existence as part of his argument to have Touma be the "scorer" or "mediator" of the magic gods in the world. Touma then notes how she shows wherever he goes. At this point however High Priest reveals that he has been joking, much to Touma's surprise.

Touma admits that he still doesn't know the headband girl's name despite being classmates with her. In the end Touma decides nothing would come of it even if he did find out her name.

Salome Arc
On December 4th, with her school unusable due to damage from the High Priest's rampage, the headband girl and her classmates moved to a nearby middle-high school to have classes in the schools' spare classrooms.

Aleister Crowley Arc
The headband girl was present on the bus which Touma's group were taking while helping Tsuchimikado Motoharu, Tsuchimikado Maika and Karasuma Fran in their attempt to escape from the city.

Toaru Majutsu no Index Light Novel Volume SS2
She appears in the background as Kumokawa Seria talks to drenched Kamijou Touma.

Toaru Majutsu no Index SS: Love Letter Competition
She is in the background peering alongside Himegami Aisa in the only illustration in the story when Kumokawa Seria arrives in their class to ask for someone to deliver a letter to Touma, who is missing.

Toaru Majutsu no Index Movie: Miracle of Endymion
She appears in the movie during the only classroom in A Certain High School, apparently enamored with the latest trend, the idol Meigo Arisa.

Trivia

 * The term used to refer to Headband girl in Japanese, katyusha, refers to the horseshoe-shaped headband she wears in her appearances. The term itself is derived from Russian, which originated from a character in 's novel Resurrection. In Britain, the katyusha is called an "alice band", and simply "headband" in the United States.