Glas loses his path in life when he pulls a "flop" during his spirit summoning ceremony. However, he is given another chance when he receives a royal order to fight in the front lines, along with the Princess's knights, as a war doctor. With his "flop" capable of curing anything, the curtains unfold upon a new fantasy war chronicle!

Narrates the story of Kyuuki, a strong, proud fox demon who recently woke up and needs a host and Kamishiro Shin, a normal would be high school student if it wouldn't be for "his ability" and for the fact that he got a hold of the black Grimoire that controls Kyuuki's existence.

Shin is bound to the book as long as he is alive, thus not only he can't sever his connection to Kyuuki; but those who want the book's power are bound to come after his hide regardless of time and place.