TV-Series
Description
Index is a petite silver-haired nun appearing 14-15 years old, with thigh-length hair and large green eyes. She wears the "Walking Church," a protective white and gold modified nun's habit replicating the Holy Shroud of Turin, now damaged and held together by safety pins after an encounter with Kamijou Touma's right hand.

Her past is obscured by enforced annual memory loss. Claiming birth and upbringing in St. George's Cathedral, she serves as the living "Index Librorum Prohibitorum," holding 103,000 forbidden magical grimoires. Selected for her perfect memory and immunity to the grimoires' corruptive effects due to her lack of mana, she cannot use magic. She traveled globally with guardians like Stiyl Magnus and Aureolus Izzard to memorize texts. To restrict access to this knowledge and prevent her potential transformation into a Magic God, the Church of England, under Laura Stuart, implements the memory erasure via a "Collar," presented as preferable to limb amputation and confinement in the Tower of London.

She arrived in Japan one year before meeting Touma, already memory-wiped. Stiyl Magnus and Kanzaki Kaori placed her in a back alley with basic magic world knowledge to evade pursuing magicians. During an Academy City blackout, fleeing her scheduled memory purge, she fell onto Touma's balcony, beginning her reliance on him as an unofficial guardian.

Her narrative role evolves. Initially central as the pursued bearer of forbidden knowledge, she shifts to a supporting role in conflicts like the Gremlin arc. She actively aids Touma during the Fall of Academy City arc, protecting him alongside allies like Othinus. Her analytical skills prove crucial, identifying and countering spells in the "Road to Endymion" story and dismantling Ladylee Tangleroad's destructive magic in the "Miracle of Endymion" movie using her grimoire knowledge.

She appears in spin-offs like "A Certain Scientific Railgun," interacting with Tessou Tsuzuri, retrieving her cat Sphynx, searching for food, and rushing to visit the hospitalized Touma during the "Sisters Arc." Cameos often highlight her gluttony, such as fighting a cleaning robot over a donut.

Side stories further illustrate her character. In "Shinyaku Toaru Majutsu no Index SS," she uses money from online puzzles to buy Touma a gift, encountering Mikoto Misaka and Kuroko Shirai. Her quick thinking and empathy resolve a conflict with the "Priestess of Bastet" by reconstructing a Book of the Dead and using the voice of the magician's lost loved one. "Bio-Hacker" mentions her in the context of Touma's middle school. Her magic analysis assists Touma against Ureapaddy Exica in "Road to Endymion."

Her relationships involve complex bonds. With Touma, it's marked by mutual dependency and protectiveness, often expressing frustration when he leaves her. Past connections with Stiyl Magnus and Kanzaki Kaori involve genuine care obscured by her memory wipes, with Kanzaki confirmed as a former best friend. The recurring memory erasure creates tension regarding forgotten bonds.