Yohei Sakaguchi, universally nicknamed King, is a fourth-year sociology student at Kansei University living in Chikusei-so dormitory. He sports a dark buzz-cut, black eyes, and a prominent nose, typically clad in a yellow tracksuit or an orange sweatshirt with grey sweatpants. As the shortest member of the dorm's running team, his physical presence is distinct.

The moniker "King" stems from his self-declared mastery of trivia, mirroring his intellectual side. Initially lacking any innate interest in running, he participates purely for pragmatic reasons. Facing imminent graduation and struggling with job hunting, he sees the prestigious Hakone Ekiden relay marathon as a potential resume booster to enhance his employment chances, highlighting his early reluctance and future anxieties.

King's personality blends sarcasm with introversion; dry humor masks underlying shyness around strangers and difficulty forming connections. His initial skepticism toward running gradually softens as he bonds with the team. Though he joined for superficial motives, shared struggles and encouragement from earnest peers like Takashi Sugiyama deepen his commitment to training. His journey reflects a shift from viewing running as a utilitarian chore to embracing it as a meaningful collective endeavor.

Before the track team, King played high school soccer for three years, a background that doesn't initially foster enthusiasm for long-distance running. His development shows incremental gains in perseverance and team cohesion, culminating in Hakone Ekiden participation. This event symbolizes both athletic achievement and personal resilience against life's pressures, particularly adulthood and identity challenges.

Throughout the series, King's interactions reveal a mix of dry wit and vulnerability. He forms part of Chikusei-so's diverse ensemble, where each member's unique traits fuel their collective Ekiden pursuit. His story arc emphasizes finding purpose through duty, camaraderie, and defying conventional expectations.