Akiko Hoshi, the protagonist’s older sister, steps into the role of a maternal anchor after their mother’s death. Growing up in a home shadowed by financial strain and a father whose emotional absence loomed large—a former baseball player drowning in alcoholism and bitterness over dashed dreams—she shouldered the weight of domestic responsibilities early, balancing caregiving, household management, and offering emotional refuge for her brother against their father’s harsh training and cutting words.

Her dynamic with her father grows increasingly fractured over time. Though she initially weathered his outbursts from a sense of duty, she steadily confronts the escalating abuse directed at her brother, especially as his relentless training leaves both physical and psychological scars. This tension peaks when her brother suffers a career-ending injury, spurring Akiko to openly defy her father’s ambitions and fiercely prioritize her brother’s recovery. Despite the rift, she intermittently bridges the gap between father and son, urging understanding without wavering in her protective resolve.

Across the narrative, Akiko stands as an unwavering pillar of compassion. Her arc shifts from quiet endurance to vocal opposition against familial toxicity, though her brother’s safety remains her compass. Her unexplained absence during pivotal moments, like a promised Christmas reunion, reverberates through her brother’s struggles, cementing her irreplaceable influence. Later installments briefly widen her presence, hinting at her continued role as a stabilizing force, while her interactions with her brother’s peers and rivals further emphasize her ability to temper the story’s high-stakes athletic drama with grounded humanity.