Index Librorum Prohibitorum/Personality and Relationships

Personality
Due to being raised in a church and having no memories of her life up until a year before she met Touma, Index is quite innocent and naive, often being elated by things that an adult or even people her age would find mundane. She is slightly ignorant and curious of modern technology, not knowing what a touchscreen was or how it worked until Kazakiri Hyouka showed her.

She is very gentle and polite with people and has a kind nature, as shown when she picked up a stray kitten and took it home, although Touma initially refused. She also, like Touma, has the trait of sacrificing herself for others sake which is why several people befriended her in the past who still keep caring for her despite her memory loss each year. Despite her naivety, Index is extremely intelligent, as a result of having the knowledge of 103,000 grimoires stored inside her. Due to her photographic memory, Index is able to remember everything in the books and often gives Touma information when needed.

She can be easily irritated especially when it comes to Touma, who usually ends up angering her in some way as a consequence of his own bad luck. He is often bitten by Index as punishment. It is a recurring gag for Index to bite Touma whenever he has inadvertently annoyed or irritated her in some way (much like Misaka Mikoto's habit of trying to electrocute him whenever she is annoyed at him), occurring even in serious situations or in front of important persons. She has even bitten him out of anger for trivial things that he has not even done. At one point, Touma even compares her to a mosquito. However, in Toaru Majutsu no Index no Subete, it is noted that it is a sign of affection towards him, as Touma is the only person whom she bites. Index can also be rather bratty at times, often getting annoyed when Touma doesn't spend enough time with her.

She also has an extreme appetite as shown when she met Accelerator and made him to spend all of his money treating her to food. In fact, the very first thing she said to Touma was that she was hungry. Index has taken a liking to the anime Magical Powered Super Android Girl Kanamin and once cosplayed as her. She has strong feelings towards Touma and even confessed her love after knowing Touma lost his memories because of her, however he avoided answering by changing the subject of the talk since he has no idea about what kind of feelings he used to have with Index.

Kamijou Touma
At the beginning of the series Touma saved Index from the fate of having her memories erased every year and she has been living with him ever since. She is in love with him but it is unknown if he feels the same towards her. She gets mad at him for going off to fight magicians without her and constantly turning up with new girls, and usually expresses her anger by trying to bite him. Index is still the only girl to have confessed her love to Touma, however, Touma avoided answering by changing the subject of the conversation since he had lost his memories, he had no idea about what kind of relationship he used to have with Index. Moreover, Index is also the first and one of the only girls known to have kissed Touma, the other being Shokuhou Misaki. This happened when she tried to bite him during the Daihasei Festival Arc, which caused her much embarrassment. In the Miracle of Endymion movie, Index mistook Arisa's question and describes her relationship with Touma to Arisa as one where Touma just feeds her.

Tsuchimikado Maika
Maika is Index's friend and the person she usually spends time with when Touma is away at school.

Kazakiri Hyouka
Kazakiri is a very special friend of Index's. They met during the Kazakiri Hyouka Arc and clicked right away. Even after learning that Kazakiri isn't human, Index didn't look at her any differently and they stayed friends.

Misaka Mikoto
Index considers Misaka as a rival in love for Touma. After their first meeting, both fought over who would stay with Touma. Both knew that Touma usually ends up in situations where he usually saves a girl's life and were angered at him when they found he saved the other girl's life. She also considers Mikoto to be lacking manners compared to Mikoto's clone, Sister 10032. Also, Misaka is embarassed to note that Index knows more about Japanese culture than she does, despite being a foreigner. Index has also given Misaka the nickname of Short Hair.

Kanzaki Kaori
Kanzaki and Index were close friends before Index had her memories erased. After Index had her memories erased Kanzaki tried to make more memories with her again, but after a while she gave up on this and allowed Index to think that they were enemies. Even though Index no longer remembers her, she is still very important to Kanzaki.

Stiyl Magnus
According to Kanzaki, Stiyl and Index were close friends before Index had her memories erased, but after witnessing her memory erasure each year, he and Kanzaki gave up on making more memories with Index and allowed Index to view them as enemies. As a result, despite the problem’s resolution, Index is still wary of Stiyl. The latter's antagonistic manners toward Kamijou Touma only serves to reinforce this fact. On one occasion, Index refers to him as a "despicable man” for his tendency to involve Touma in the Magic side’s affairs.

Meigo Arisa
Meigo chronologically meets Index prior to the "Miracle of Endymion.", and they are apparently friendly enough with each other to have a nice dinner out at a certain family restaurant.