The 9th item in the Magical Girl Lyrical Nanoha StrikerS Device Charm Collection comes in a set of two tomes: The Book of Darkness that is used by Hayate Yagami, and The Book of the Azure Sky held by Reinforce Zwei. The two books used to store extensive magical data have been impressively recreated with finely detailed etchings. Each of the charms is different, so find the one that suits you.