Hanabusa is a mysterious figure in Beautiful Bones: Sakurako’s Investigation, serving as a primary antagonist whose shadow looms over several cases. He is a painter by profession, yet his activities extend far beyond art into the realm of calculated criminality. His physical appearance is striking and distinctive; he has no hair on his entire body except for the top of his head, a feature that contributes to his unsettling presence.

The core of Hanabusa’s personality is defined by profound manipulation and a grandiose self-perception. He presents himself not merely as a man but as an angel sent from God, indicating a deeply held belief in his own superiority and divine purpose. This god complex fuels his interactions with others, whom he views as tools to be shaped and controlled. He is a consummate manipulator, using psychological tactics to enthrall his victims. On at least one occasion, he convinced two young women, Hitomi and Minami, that he was in love with them, a deception that led them to allow him to carve butterfly patterns into their backs. His methods are subtle and insidious rather than overtly violent, preferring to poison minds before bodies.

Hanabusa’s motivations are rooted in a twisted form of artistry and control. He seems driven to create his own macabre masterpieces using human lives as his medium. A powerful symbol associated with him is the Lethe diana butterfly, a motif that appears in his schemes and connects his various crimes. This butterfly imagery, linked to a drug called "the butterfly" mentioned by a previous offender, suggests a pattern of behavior or a signature he leaves on his work. His ultimate goal is not simply to kill but to dominate and reshape the wills of those around him, solidifying his self-styled role as a divine arbiter of fate.

Within the story’s structure, Hanabusa is the overarching antagonist whose presence is felt long before he is fully confronted. He is first introduced indirectly as a Chekhov's Gunman, when a character named Takeshi is advised by him on a painting that turns out to be poisoned. This early case establishes his modus operandi: using art as a vehicle for harm. He is later given the nickname the Sphenoider, a reference to his habit of removing the sphenoid bone from the skulls of his victims in several unsolved cold cases. This specific, ritualistic act ties him to a series of deaths and marks him as a unique kind of predator. As the series progresses, he becomes the arch-enemy of the protagonist, Sakurako Kujo, and is ultimately revealed as the Big Bad pulling strings from the shadows. The cases connected to him are notably darker in tone than others, marking him as a Knight of Cerebus whose very presence elevates the stakes and the sense of dread.

Hanabusa’s key relationships are defined by opposition and victimization. His most significant foil is Sakurako Kujo, the brilliant osteologist who makes him his natural enemy. Their conflict is personal, as Hanabusa may be connected to tragic events in Sakurako’s past. It is strongly suspected that he was responsible for poisoning her beloved pet cats when she was younger, and his machinations are also linked to the death of her younger brother, Soutarou. These acts were possibly intended as warnings to her uncle, who was investigating the Sphenoider, turning Sakurako’s professional pursuit of justice into a deeply personal vendetta. He maintains no genuine relationships, only a network of thralls and victims he has hypnotized or seduced into servitude, using them to do his bidding while he remains at a remove from the physical act of killing.

Hanabusa does not undergo a traditional character arc or development within the series, instead remaining an enigmatic and persistent threat. One of the most defining aspects of his role is his status as a Karma Houdini; by the end of the anime, he has yet to be brought to justice for his many crimes, leaving his story unresolved and his danger still present. His lack of development is a deliberate narrative choice, preserving his aura of mystery and menace as an elusive force of chaos.

His notable abilities are primarily psychological and chemical rather than physical. He is an adept hypnotist, capable of enthralling people to follow his commands without question. This power allows him to orchestrate crimes and manipulate others into becoming his pawns, keeping his own hands clean. He is also a master poisoner, adept at creating and deploying toxic substances, as demonstrated by the poisoned painting. This combination of hypnosis and poison expertise makes him a uniquely dangerous adversary, one who corrupts the mind and destroys the body with equal skill.