Like most Beastfallen, the half-tiger Mercenary hates witches, but when he's rescued by an odd young woman who turns out to be the witch Zero, he finds himself agreeing to help the annoying magic user search for a missing grimoire. That, unfortunately, means that they could be stuck together for a long time, which becomes increasingly uncomfortable as she inexplicably thinks his feline form is a nice place to nap on! Still, if they succeed, she'll make him human, and as the book contains secrets that could destroy the world, can he really afford to not join her quest for the GRIMOIRE OF ZERO?