The Shirushi (印, Sigil), otherwise known as "Hakyoku's Brand", was one of the more direct means favoured by the fallen Tenjin, Hakyoku, to control and empower his closest followers. It was widely abused by Shinzō, himself a follower who served as Hakyoku's proxy, to control the Imawashī criminal organisation.
The Shirushi began as a means of granting those favoured by Hakyoku enhanced longevity, in keeping with the fabled "Gift of the Tenjn". It would later be warped by Hakyoku following his banishment from Amenokai. While their body would eventually age, the soul would not. Those branded in this manner could jump between active brands, effectively gaining a form of immortality. However, with no active brands, then the soul would die; this weakness was exploited by Shigeru Yūdai and Kentaro Hiroshi upon the latter's defeat of Shinzō. When Shinzō's own body was destroyed he attempted to infiltrate Shigeru, only for the latter to overpower Shinzō's consciousness with his superior will, at which point he ordered Kentaro to euthanize him.
The Shirushi came in three distinct stages; each stage was noticeably more advanced than those that preceded it. This was born from Hakyoku's desire to escape his prison and avenge himself upon Ikusa, otherwise known as the Yellow Dragon God, and The Balancer, otherwise known as the Soul King. As he was limited by his prison and by his constant battle of wills with Ikusa, Hakyoku required a subtle means of manipulation: thus was the Shirushi warped into a tool of domination. Through Shinzō and many other like-minded individuals Hakyoku directed matters from behind-the-scenes, all-the-while keeping Ikusa in the dark regarding the actions of those he ensnared.