Dobhailen Isolde, one of the Hawthorn group's most prized and powerful slayers not to mention being dubbed as the “Cold-hearted King” is requested to do a seemingly simple mission of eliminating a demon commissioned by an unlikely client, an extravagantly dressed vampire named Hatim Kaisra. Hesitating to accept the request from the mysterious client, Dobhailen accepts it due to the fact of the large sum of riches offered by the vampire. However, this mission has more dangers and twists than the two would ever expect.