Hiyoshi is the captain of the Vampire Countermeasure Division within the Kanagawa Police Branch. He is also the older brother of the vampire hunter Ronaldo and his younger sister, Himari. At thirty years old, his career as a frontline hunter was cut short after he was bitten by a vampire, an injury that forced him into an early retirement and ultimately led to his administrative position. Physically, Hiyoshi is a short man with a youthful appearance, silver-white hair combed back, and blue eyes. A defining and recurring visual trait is his detachable fake mustache, which he frequently loses, as his face cannot naturally grow facial hair.

In his role as a captain, Hiyoshi typically presents a serious and professional demeanor appropriate for his rank. However, beneath this exterior lies a personality with notable flaws. He shares his brother Ronaldo's reputation for having perverted habits. His original drive for becoming a vampire hunter was not rooted in a sense of duty but rather a desire for self-glory, confidence, and fame, primarily as a means to attract women. This vanity adds a layer of comedic complexity to his character, contrasting with his official responsibilities.

Despite these shortcomings, Hiyoshi genuinely cares for his siblings. He holds a deep affection for both Ronaldo and Himari, although this relationship is complicated by the fact that his younger brother harbors an intense and extreme admiration for him. Hiyoshi struggles to navigate this hero worship, feeling uncomfortable with the pedestal on which Ronaldo has placed him, especially given the less-than-heroic reasons for his own departure from active hunting.

Within the story's structure, Hiyoshi serves as the direct supervisor to fellow vampire hunters Hinaichi and Handa. His position as captain places him in a position of authority, overseeing the operations of the division from a managerial standpoint rather than engaging in direct combat. His relationships are central to his role, acting as a bridge between the professional world of vampire countermeasures and the personal dynamics of his family. His past as a professional hunter, which ended in disgrace, creates an interesting contrast with Ronaldo's active career, as Ronaldo became a hunter to honor the legacy he mistakenly believes his brother left behind.

Regarding notable abilities, Hiyoshi was formerly a skilled professional hunter, but his proficiency has been permanently diminished. The vampire bite that ended his career damaged the grip strength in his arm, specifically weakening his ability to hold and fire a gun effectively. This physical limitation is the primary reason for his pivot to a desk job, though he has also been the victim of additional humiliating vampire attacks, including one from a badger game vampire. His most iconic prop, the fake mustache, can be considered a notable characteristic, as its frequent disappearance is a running visual element of his appearance.