Hiruko is a character from the fantasy world of Amawakuni, where he serves as a Zokushou, a subordinate official, to one of the powerful Twelve Shinsho. He is the personal favorite of Yorunami, the Shinsho who commands the element of water, and governs the commercial town of Suzukura on his master's behalf. In his official capacity, he is responsible for collecting taxes and controlling access to the town.

Physically, Hiruko is an adult male with black hair cut at ear-length and brown eyes. He is noted for a distinctive appearance that includes multicolored hair and glasses. His personality is complex and layered, shaped by a past in which he originally had no name and was forgotten by everyone around him. After Yorunami gave him his name and position, he became forlorn and developed a deep disdain for humanity, which he views as inherently selfish and greedy. He believes people are only interested in money and will turn their backs on others to enrich themselves.

In public, faced with a group seeking to meet Yorunami. The protagonist, Hinohara, challenges Hiruko's cynical worldview by teaching him that people value him for his genuine personality, not simply for the jobs or money he provides. This lesson has a profound impact, leading Hiruko to willingly submit to Hinohara and express his belief that Hinohara will ultimately save Princess Kikuri.

Hiruko's key relationship is with his master, which deforms upon touch. This unique ability allows him to produce coins and currency, making him a figure of immense practical power in the commercial sphere. His role in the story serves as a significant test for the protagonists, forcing them to confront not just a physical opponent, but a philosophical one whose distrust of human nature must be overcome to secure his help and advance on their journey.