Kaori explain she uses a Rune to repel people from coming here and asks Tōma to hand over Index which he refuses. He is easily beaten by Kaori's swordsmanship and wire techniques and wonders why she didn't kill him in the first place. Backing off a little, Kaori admits that she’s not doing this because she likes to, and she explains, to Tōma surprise, she belongs to Necessarius, just like Index. In fact, Kaori calls Index a dear friend and claims that she didn’t intend to hurt Index - she only wanted to secure Index as she didn't know her magical garb was destroyed, so that Index can live. The reason for all this is Index’s perfect memory ability. She explains that the capacity of human brains are small, but forgetting unneeded memories is part of organizing the brain. Index can’t do that, so her memory is quickly filled with trivial stuff. With 85% of her memory devoted to the 103,000 magic volumes, the other 15% fills up quickly and needs to be erased or else Index will die from information overload. They do this every year, and there are only three more days before it needs to happen again.
She asked Tōma to hand over Index again since she's not gonna remember him but Tōma refuse citing if Kaori care about Index that much, shouldn't she tell her about everything to end the misunderstanding between the two. However this only angers Kaori who starts beating Tōma as she lashes out on how he doesn’t understand how she and Stiyl feel. They try everything to ensure Index always remember them including giving her a diary but no more how much they try, it still didn't work to the point it was unbearable for them to see her smile. Nevertheless, he tells her they were inconsiderate of Index feelings as they were leaving a scare young girl who had no idea what was going and they did nothing to help and feels that if they have given her even happier memories in the next year, and let her know that there’s happiness waiting for her, she won’t be afraid of losing her memories, then there’s no need to run away anymore before he loses consciousness and questions Kaori why she became strong and who she wanted to protect with her strength.
Three days later, Tōma wakes up in Komoe's apartment and finds Index taking care of him. Index feels responsible for what happen to Tōma but he ease her mind. Kaori and Stiyl arrives at the apartment, but Index tries to make them go away and attempts to protect Tōma by saying that she’ll do whatever they want.