Atsumu Miya, a second-year at Inarizaki High, is the setter for the school's volleyball team. He sports golden-yellow hair swept to the right and often wears confident or smirking expressions. His personality blends carefree demeanor with fierce competitiveness, demanding perfection from himself and teammates. He directly confronts spikers who fail to score from his sets, exemplified by questioning middle-school teammates after a loss about why they couldn't hit his "perfect tosses." This attitude made him unpopular then, though he remained indifferent to their opinions. He played volleyball alongside his twin brother, Osamu Miya, since elementary school. In fourth grade, they attended a volleyball workshop where they met future teammate Aran Ojiro and adopted the nicknames "Tsumu" (Atsumu) and "Samu" (Osamu). The twins developed remarkable synergy over years of play, earning recognition as "volleyball celebrity twins." Despite frequent arguments—like Atsumu calling Osamu "a useless piece of trash" during a poor game—their bond underpinned Atsumu's growth. Aran observed that Atsumu's greatest advantage was having Osamu as a constant rival and companion, ensuring mutual progress. His playing style showcases sharp observation and adaptability. As an ENTP, his dominant extraverted intuition (Ne) rapidly analyzes patterns, allowing him to replicate techniques like Karasuno's "Freak Quick" without practice. Auxiliary introverted thinking (Ti) enables precise execution in unfavorable conditions, driving his commitment to deliver perfect tosses even from low or awkward positions; he asserts a setter must pass perfectly regardless. Tertiary extroverted feeling (Fe) sometimes surfaces as blunt provocation, such as taunting opponents like Kageyama as a "goody-two-shoes." Post-high school, Atsumu joined MSBY Black Jackal and the Japanese national team, competing in the 2021 Olympics. This diverged from Osamu opening an onigiri shop, causing initial tension until they reconciled by challenging each other to "see who lives a happier life." Despite separation, Atsumu visits Osamu for support, notably while refining serves. During a Black Jackals match, Osamu critiques Atsumu's persistent ambition, chiding him for "try[ing] too hard to look good" after a missed serve. Professionally, Atsumu sets for former rivals like Hinata, fulfilling his high-school promise to do so "someday." Throughout his journey, Atsumu retains core competitiveness and perfectionism while gaining self-awareness. His relationship with Osamu evolves from codependent reliance to mutual respect for independent paths. His philosophy, "The strong one doesn’t win; the one that wins is strong," fuels his relentless drive for victory and self-improvement across all stages.