Chairman is a supporting character in the film, primarily defined by his role as the wealthy and ambitious grandfather of Yuho, one of the main human characters. His background is rooted in the history of the film's setting, the small fishing town of Hinashi. He was the original builder and owner of Merfolk Land, a now-derelict amusement park located on the island just off the town's coast. The park, themed around the local legends of merpeople, was a commercial failure, leaving him with a strong desire to reclaim his former success and financial standing.

In terms of personality, Chairman is depicted as a blowhard and an opportunist, driven more by the prospect of profit and grandeur than by the superstitions of the townspeople. He is a figure of some authority and wealth in Hinashi, which gives him a certain degree of influence. His motivations become clear when Lu, the young mermaid, gains attention for her enchanting singing and dancing. Seeing her popularity as a way to revitalise his failed business venture, he seizes the opportunity to reopen Merfolk Land, positioning Lu as the star attraction. This plan is central to a significant portion of the story, as his scheme to use Lu for a grand reopening performance creates both opportunities and conflicts for the main characters.

Chairman's primary role in the narrative is as a secondary antagonist or an antagonistic force of circumstance. While not malevolent in a monstrous sense, his greed and single-minded pursuit of his own goals put Lu and her friends in danger. He represents the exploitative nature of adult commercial interests clashing with the pure, innocent joy that Lu embodies. His actions escalate the central conflict; he is responsible for capturing Lu and her father in an attempt to control them, which directly triggers the ancient curse that threatens to flood the town.

His key relationship is with his granddaughter, Yuho. As her grandfather and a prominent local figure, his actions directly affect her. However, his relationship with her is secondary to his business ambitions. He shows little concern for the teenagers' feelings or their band, Seirën, viewing them merely as a vehicle for his commercial comeback. This creates a point of tension for Yuho, who struggles with jealousy over Lu's talent and the attention she receives, a situation her grandfather's plans only exacerbate. He has no direct relationship with the film's protagonist, Kai, other than as an adult authority figure whose ambitions drive the plot.

There is little to no character development for Chairman. He remains a static figure of avarice throughout the film. His scheme ultimately fails when the curse is unleashed and the merfolk must leave the town. Because the narrative focuses on the growth of the younger characters, he serves as a fixed obstacle for them to navigate rather than undergoing any personal transformation himself. He has no notable supernatural abilities, his influence stemming entirely from his money, position, and the authority he holds as an elder in the community.