In Haikyuu!!, the theme of gender in sports is explored through the representation of female characters like Yachi Hitoka and Kiyoko Shimizu, who are portrayed as strong, competent individuals involved in the volleyball world. While the focus of the series is primarily on male volleyball teams, the female characters are given significant screen time and are shown to have their own challenges and successes within the realm of sports. Haikyuu!! highlights the importance of dedication, teamwork, and passion for the sport regardless of gender, ultimately promoting inclusivity and equality in the world of athletics.