Necessarius

T1 E3: After Tōma leaves, Komoe successfully helps Index heal her wounds using an ancient magic ritual but asks Tōma the next morning who she is. When he lies that she is his sister, Komoe spots the fib immediately but decides not to press the issue since she believes it is something he must solve on his own. While Komoe goes out to shop, Tōma learns that Necessarius, the organization that Index belongs to, implanted the Index Librorum Prohibitorum into Index's mind so that she would be a living library for the Church, since reading the originals would curse and taint people. Meanwhile, Stiyl and Kaori continue to watch Index and comment on how her happiness will be short-lived. When Tōma and Index get into a fight and separate, Tōma finds himself in an empty street and meets a girl wielding a nodachi, which so happens to be Kaori.