Mina Hidaka served as a nurse at a mountain clinic in Miyazaki Prefecture. Diagnosed with malignant melanosarcoma during her second year of high school, she faced a drastically shortened life expectancy.

While accompanying a young Giants fan patient to a Yomiuri Giants training practice, Mina witnessed the child injured by a stray baseball deflected by pitcher Hyūma Hoshi. She confronted Hyūma fiercely about the incident. After hearing his explanation, she slapped his cheek and attempted to carry the child back to the clinic. Hyūma intervened, carrying the child himself on his back, aided by his teammate Chūta Ban.

Following this event, Hyūma began frequenting Mina's clinic. Their bond deepened through these encounters. During a meeting on a beach one evening, Hyūma confided in Mina about his harsh childhood, demanding father, personal struggles, and dream of becoming a star player for the Giants. In turn, Mina revealed her terminal illness and inevitable fate. She became Hyūma Hoshi's lifelong love interest.

Mina Hidaka died soon after. Witnessing her body triggered an intense mental breakdown in Hyūma. Her death precipitated a sharp decline in his pitching performance and plunged him into depression. At her funeral, Hyūma placed a lily on her open casket, vowing she would remain his only true love and declaring he would never be involved with another woman.

Her relationship with Hyūma ended prematurely due to her death. The profound emotional impact of her loss continued to shape Hyūma's professional career and mental state in the years that followed.