Gakiken, "spirit-sword", was the most well-researched book on ghosts and hauntings. Written by Toritaka Iemasa in the 9th century, it gave birth to the romanticized image of the Phantom Hunters. Since the book was written by a former Kitsu family, it formed good relations between the Toritaka and Kitsu family, allowing some Toritaka bushi to train with the Kitsu.