Book of the Dead (死者の書 Shisha no Sho?) is an Egyptian grimoire. First mentioned in the first Toaru Majutsu no Index light novel volume by Index Librorum Prohibitorum as one of the "representative" grimoires in her head, it later plays a central role in Shinyaku Toaru Majutsu no Index SS.
The Book of the Dead is made of papyrus, and is buried in the pyramids with the mummies. Unique to the grimoire is that it is not a single book with a decided format, as its contents can be custom made depending on the person it will be altered for.
Made for people like the pharaohs, its primary purpose was to be buried in the pyramids with the mummies in order to one day return the pharaoh's soul to the world. Unlike other grimoires, it is not a single book with a decided format. In order to allow the pharaoh to return from the underworld, each individual copy must be custom made in accordance with the specific pharaoh’s deeds and sins. For that reason, a new grimoire must be made each time a new person dies. The grimoire contains not only text but illustrations and diagrams as well.
For Index Librorum Prohibitorum, she has a copy of the Book of the Dead, though it is unknown for whom the copy she has is for. She later acquires a copy of the Priestess of Sekhmet's Book of the Dead after it was reconstructed in her head through the manipulations of Leep, the Priestess of Bastet, as well as the copy of the grimoire that was already inside Index.
The original physical copy of the Priestess of Sekhmet's Book of the Dead is mostly intact apart from the diagrams on account of grave robbers, leading for Leep to reconstruct it using Index. It is likely that Leep still has the physical copies with her.