Daisuke Yamanaka, a 45-year-old member of the Eternal Boys idol group, previously worked as a manager in the Management Department of Manpuku Entertainment Productions. Early popularity as a model ended with expulsion from the industry due to behavioral issues, leading to significant struggles that altered his life's trajectory. He feels profound indebtedness to Manpuku Entertainment's previous president, who offered him the managerial role during his lowest point, fueling his unwavering loyalty and determination to support the company. His background shows early success bred overconfidence, contributing to professional setbacks before joining the agency.

The concept for Eternal Boys originated directly from Daisuke's experiences and his dedication to reviving Manpuku Entertainment. He joined the group as a performer to actively contribute to the company's revival, balancing his background as a talent agent with his new frontline role. His deep personal investment in the group's success stems from his commitment to honoring the previous president's legacy and ensuring the agency's survival. His journey involves adapting to the physical and social demands of being a middle-aged idol while maintaining his inherently nurturing and supportive nature towards fellow group members.

The etymology of his name reflects aspects of his character: "Daisuke" (大輔) combines "big/great" (大) and "help" (輔), while "Yamanaka" (山中) means "mountain" (山) and "middle" (中). His development highlights the transition from a behind-the-scenes manager to a performing idol, driven by loyalty and a desire to prove new beginnings are possible at any life stage.