Jin Munakata's childhood was defined by abandonment and tragedy; his father's departure led directly to his mother's death from despair, after which his grandparents raised him. His paternal half-sister, Ranko Midorikawa, developed profound admiration for him.

Munakata first achieved fame as a Davis Cup champion tennis player. A leukemia diagnosis abruptly ended his athletic career and imposed a limited life expectancy. This prognosis fueled his subsequent dedication to coaching, driven by a desire to cultivate future tennis talent within his remaining time.

As coach at Nishi High School, Munakata employed rigorous, often unorthodox methods emphasizing mental fortitude alongside physical skill. He possessed an exceptional eye for potential, most notably selecting inexperienced freshman Hiromi Oka for the team's top roster over seasoned players, solely based on perceived latent talent. His coaching philosophy demanded extreme emotional discipline; he explicitly forbade Hiromi from pursuing romantic relationships, including her attraction to fellow player Takayuki Todo, insisting tennis required her complete focus.

Characteristically stoic and reserved, Munakata rarely displayed overt emotion. This outward sternness coexisted with a deeply caring commitment to his players' growth, particularly Hiromi's, forming a complex mentor-protégé bond central to her development. He privately bore his deteriorating health throughout his coaching tenure.

Munakata died while Hiromi and key players, including Todo and Reika Ryuzaki, competed internationally in New York. His death was deliberately concealed from Hiromi during the tournament to protect her focus, though Todo learned of it and suffered immediate performance decline due to shock. The news triggered a severe psychological collapse in Hiromi upon her return to Japan, manifesting in near-catatonia. Ranko similarly abandoned tennis temporarily, processing her grief alone through intense, self-destructive practice in Australia that resulted in a serious arm injury.

His legacy persisted through his writings, particularly a diary and detailed coaching notes. These became crucial to Hiromi's recovery and continued advancement in tennis under the guidance of his friend and former playing partner, the monk Daigo Katsura. Munakata's influence extended beyond his death, shaping Hiromi's ultimate reconciliation with her passion for the sport and her confrontation of top-level international competition.