Keiji Maezono is a prominent character within the story, serving as a major rival to the protagonist Eiko Tsukimi. He is established as a supremely talented and multifaceted artist who is highly proficient in singing, dancing, songwriting, music composition, and choreography. This combination of skills has earned him a large and dedicated following, positioning him as a powerful figure in the music industry.

In terms of personality, Maezono is portrayed as a calculating and ruthlessly pragmatic individual. His actions are driven by a strong will to win and a belief that success justifies aggressive tactics. Rather than relying solely on talent, he frequently employs his significant financial resources and influence to manipulate situations to his advantage. At a major music festival called Summer Sonia, he orchestrates a scheme to sabotage Eiko's performance by using his wealth to have his associates block the bridge leading to her stage, drastically reducing her audience. He further undermines her by successfully recruiting a key member of her team, the rapper Kabetaijin, to his own side. These actions demonstrate a willingness to use underhanded methods to eliminate competition, making him a formidable and unscrupulous antagonist.

Maezono's primary motivation is to secure victory and prove the superiority of his methods, which contrast sharply with Kongming's strategic but principled approach. His role in the story is that of a direct and powerful obstacle. The central conflict of a major story arc revolves around a direct competition between him and Eiko, overseen by the strategist Kongming, to see who can draw the largest crowd to their respective stage at the Summer Sonia festival. He is framed as Eiko's biggest rival, and his history with Kobayashi, the owner of the BB Lounge where Eiko performs, is noted as a key factor that intensifies their competitive relationship.

The character has one significant relationship that shapes his past. He has an inseparable connection to Owner Kobayashi, though the specific nature of this history is not detailed in readily available information. His relationship with Eiko is purely antagonistic, defined by his attempts to crush her career. He also interacts with other artists in a transactional manner, as seen when he effectively holds the duo EastSouth under his thumb before they are pulled away from him by Kongming's strategy.

Keiji Maezono demonstrates notable development through his role as an antagonist. Rather than following a path of redemption, he remains committed to his ruthless ideals even in defeat. A flashback into his past is said not to redeem his character but instead reinforces his unpleasant and self-serving nature, and he retreats from the competition while still standing by his core beliefs. This makes him a uniquely consistent and realistic villain who does not waver from his worldview.

His abilities are his primary source of power. He is a remarkably skilled and self-sufficient artist, capable of producing his own music and choreography, which forms the legitimate foundation of his fame. However, his most dangerous abilities in the context of the story are his strategic use of wealth, influence, and manipulation. He effectively uses financial power to create logistical obstacles for his rivals and to poach talent, demonstrating an understanding of how to control the business side of the music industry to secure victory.