Kousei Amanuma is a supporting character in Blue Giant, a professional jazz pianist and the keyboardist for the acclaimed band Act. He is a well-known public figure in the Japanese jazz scene, recognized not only for his performance skills but also for his role as an outspoken jazz critic. Amanuma frequently appears on television and in other media, where he shares his pointed musical insights and critiques. His strong opinions and technical expertise have made him a familiar face to audiences beyond live music venues.

Amanuma possesses a highly refined set of abilities. His piano playing with Act demonstrates a sophisticated command of jazz harmony and rhythm, earning him national recognition. As a critic, his deep understanding of the genre allows him to articulate what makes a performance compelling or lacking, which often influences public perception of up-and-coming musicians.

His personality is characterized by a forthright and opinionated nature. Rather than softening his views, Amanuma delivers candid evaluations that command attention. This directness underscores his commitment to musical integrity and sets a high bar for fellow performers. The series presents him as an authoritative voice in the jazz community, with the weight of his words stemming from both respected artistry and a reputation for uncompromising judgment.

Amanuma’s role primarily functions as an outer layer of the jazz world that the main trio JASS must encounter and eventually earn recognition from. He embodies the established, professional side of the industry, acting as a benchmark for excellence. While the story focuses on the growth of the young musicians, Amanuma’s presence as a media critic and veteran pianist adds a layer of realism about the obstacles and scrutiny aspiring artists face. His relationship with the protagonists is largely that of an evaluator and an indirect gauge of their progress; his reactions to their performances help signal when JASS is reaching a level worthy of serious critical attention. The available narrative does not detail a specific backstory or personal arc for Amanuma beyond his established status as a distinguished performer and commentator.