The character known as Boss is the top leader of the criminal organization that employs the legendary assassin known as The Fable. Maintaining a low profile to hide his true identity, he runs a chiropractic clinic in Saitama as a civilian front.

In terms of personality, Boss is portrayed as a courageous individual who, fitting his position as the organization's leader, tends to view situations from a broad perspective when making decisions. Despite his professional role at the head of a group of contract killers, he is characterized as a cold-blooded chief executive. His worldview is pragmatic and forward-looking; he judges that the traditional contract killing business cannot continue operating in the same way as in the past due to changing times, and as a result, he actively seeks to reorganize his organization for the modern era.

Within the story, Boss serves as the primary authority figure who gives orders to the protagonist, Akira Sato (the operative known as The Fable). It is on Boss's orders that Akira is forced to take a one-year sabbatical from killing and relocate to Osaka to live as an ordinary citizen. This directive forms the central premise of the narrative. Boss discovered Akira as a child when he recognized the boy's exceptional talent and brought him into the organization, overseeing the extremely harsh training that shaped Akira into a professional killer. As the only family Akira has ever known, Boss occupies the role of his sole parental figure and personal connection outside of work.

Regarding his abilities and resources, Boss displays a surprising affinity for advanced technology. He is known to employ nanotechnology and micro-weapons that have not been disclosed to the public, giving him access to cutting-edge tools for espionage and combat. His authority within the criminal underworld is absolute, and he wields significant power, with information indicating that he was responsible for wiping out a rival organization known as Rumor in the past.