Jin Sagami endured a strict upbringing under doctor parents who mandated rigorous medical studies. Childhood visits to their hospital fostered a formative attachment to a female patient with terminal leukemia; her death profoundly impacted him. Her shifting attention towards televised idols before passing away directly motivated his career choice, aiming to capture such intense admiration. He rose as a "Super Idol," dominating the industry during the "Idol Winter" period, overshadowing contemporaries and becoming its perceived "saving grace." Collaborations with RYUSEITAI earned him the designation "Ryusei Rainbow," but tensions flared when audiences exclusively favored him, leading to disputes and the partnership's dissolution. His stage persona cultivated romantic intimacy, addressing fans singularly as "you" to simulate a boyfriend illusion. Exploitative management subjected him to grueling dawn-to-late-night schedules, even coercing him to announce his brother’s death during a live performance to manipulate sales. Exhaustion drove overt rebellion: drinking, smoking, and womanizing to provoke industry backlash. Though the public perceived this as defiance against corruption, Jin viewed it as self-destructive provocation aimed at termination. He retired around age 22, receiving a peaceful industry send-off despite his actions. Initially critical of the "Five Eccentrics" system during the War Era, he later came to appreciate its unit-based mutual support, contrasting it with his solitary struggles as a solo idol. Post-retirement, Jin reconciled with his parents, who had disowned him during his idol career over undisclosed conflicts. They welcomed him back after retirement, expressing anxiety over his scandals. He transitioned into education and idol support, becoming a general education teacher and sports doctor at Yumenosaki Academy while working in Ensemble Square’s business department. His teaching style is informal and approachable, though his unkempt appearance—messy hair, frequent stubble, stained lab coat, and green slippers—and self-neglect draw mixed student reactions. He often isolates in the infirmary yet demonstrates genuine care for students’ well-being. Professional duties include organizing inter-agency projects like "Get Island" and "Wedding March!" and MCing events, leveraging his legacy status. He maintains a longstanding, complex friendship with Akiomi Kunugi, whom he met during his third year at Yumenosaki. Though initially annoyed by Akiomi’s enthusiasm, Jin developed protective instincts and supported his succession as a top idol; their bond includes regular drinking outings. Jin participates in initiatives like "Project Saga," focused on reviving retired idols, where promotional materials reframed rival Sazanami Jun’s backstory into one of admiration for him, causing Jun discomfort. During "Bogie Time" events, Jun impersonated him under agency directives, further intertwining their narratives. His current activities involve judging auditions like the "4piece" program and facilitating youth idol development through Ensemble Square, though he finds modern industry trends challenging to navigate.