The No-Name Grimoire, also known as the Blank Grimoire, is a Grimoire that originally took the shape of a book. It can copy the code of any other Grimoire, even becoming an Azure Grimoire. There seems to be no limitation on what it can copy, even being able to mimic Vision, which is an ability.
Mai Natsume is currently fused with the Grimoire as a Remix Heart. It was originally in the library of the Hazuki estate before Mai stumbled across it. [1] The Grimoire can only inhabit the body of a woman, so it changed her body from a man's to a woman's. [2] When being used, Mai becomes much stronger and faster, her pupils becoming white rectangles.