Remix Heart

A Remix Heart (リミックスハート) is a unification of a human and a Grimoire. Mai Hazuki is the only known Remix Heart, as she is a human vessel of the Nameless Grimoire, and, for a time, the Intermediary Grimoire.

A Remix Heart is required to smelt the Crimson Grimoire, which was researched by Sypher Alvar.