The Hypnagogia Grimoire is a Grimoire in the shape of a picture book. It is a Grimoire that can enter a person's dream as they sleep.
The dreams created by the Hypnagogia Grimoire are said to be incredibly enjoyable, but this is dangerous as some people will wish to stay inside the Grimoire and not want to wake-up, remaining in their dreams. Anything drawn in the book will be made real, but the copies are remarkably weak - a drawing of Hakumen was easily beaten by Makoto Nanaya.
The Grimoire temporarily entered the dreams of Mai Natsume, but the combined efforts of Team Remix Heart saved her. The Grimoire can show visions of the future and create terrifying nightmares, but this can allow the user to awake. 
- BlazBlue: Remix Heart, Chapter 08