Hitoka Yachi, a petite first-year student at Karasuno High standing 149.7 cm (4'11.5") tall and weighing 42.5 kg (93.7 lbs), joins the boys' volleyball team as a manager trainee. Recruited by Kiyoko Shimizu seeking a replacement before her graduation, Yachi initially agrees while flustered by the request, having not joined any club. Despite early intimidation, she quickly grows fond of the team. Her appearance, noted as cheerful and cute by others, features chin-length blonde hair typically in a side ponytail adorned with colorful star accessories and light brown eyes. Post-timeskip, her hair is slightly longer and usually tied back. Yachi's personality is marked by extreme nervousness and an overactive imagination, leading to snap judgments—mistaking Hinata for a manager due to his height or suspecting Coach Ukai of being a dangerous stalker—for which she frequently apologizes. She struggles with self-worth, underestimating her importance despite strong organizational skills and curiosity. Influenced by her mother Madoka Yachi's graphic design profession, her meticulous note-taking leads her to tutor Hinata and Kageyama academically. Though timid, she is genuinely kind, attentive to others' emotions, and proactive in supporting the team. Over time, she learns to voice anxieties openly, later sharing this strategy with Yamaguchi. At home, her mother works long hours at a design company, often leaving Yachi alone. This exposure shapes her design approach for tasks like club posters and notes. Her mother cautions against half-hearted commitment to the team, urging dedication if she joins, prompting Yachi to confront insecurities and resolve to become manager—a declaration that visibly moves her mother. Yachi's development involves gradual team integration. After overhearing funding issues for a Tokyo camp, she designs a promotional poster featuring Hinata, securing donations with her mother's professional help, solidifying her role. She mediates conflicts, like Hinata and Kageyama's fallout over the "quick attack," providing emotional support and practical assistance such as tossing balls for Kageyama's solo practice. Her timid cheering during matches evolves into enthusiastic support, reflecting growing confidence. Observational skills aid match analysis, noting opponents' tactics or team dynamics. Key relationships define her journey: Kiyoko mentors and protects her, easing her into the role. Hinata becomes a close friend whose encouragement helps her assert herself; she supports him emotionally post-conflicts with Kageyama. Though initially intimidated by Kageyama, she assists his training and offers disguise advice during reconnaissance. Her bond with the team collectively helps overcome self-doubt as she admires their determination. Post-timeskip, Yachi attends college and plans to work at an ad design company in Tokyo after graduation, aligning her design background and managerial experience.