Kentarō Sanada, a 40-year-old former salaryman, spent 17 years as a Sales Department Manager in an advertising agency until sudden bankruptcy left him unemployed. Struggling to find new work amidst repeated rejections and nearing the expiration of his unemployment insurance, his previously passive life, marked by a lack of deep engagement in any pursuit, was thrown into uncertainty. Desperate for employment, he applied to what he believed was a conventional job at Manpuku Entertainment Productions, unaware it was an audition for an idol group. He unexpectedly found himself accepted into Eternal Boys, a group of six middle-aged men with no prior idol experience.

This drastic career shift propelled him far outside his comfort zone, demanding adaptation to singing, dancing, and performing despite initial difficulties and intense self-doubt. His nervous disposition and struggle to adjust were evident. His journey involved rigorous training, navigating complex group dynamics, and striving to establish Eternal Boys in an industry dominated by younger talent. Internal conflict about his place in this new world even led him to consider quitting. Yet, he persevered alongside his fellow members. Together, they faced professional hurdles including CD debut preparations, participation in events like the Men's Idol Fest, and managing interpersonal issues within their shared living and working environment.

The group ultimately achieved significant milestones, culminating in a performance at Budokan, symbolizing their growth and resilience. Their story continued in the film *Eternal Boys NEXT STAGE*, following experiences beyond the initial series. Throughout, Sanada's background as a corporate employee grappling with unemployment and reinvention remained integral to his character arc, highlighting his transition from conventional office life to the demands of the entertainment industry.