In Haikyuu!!, the concept of self-improvement is a central theme that is portrayed through the main characters' dedication to continuously learn, grow, and push themselves to become better players and individuals. The show highlights the importance of hard work, perseverance, teamwork, and overcoming personal challenges to achieve one's goals. Through intense training, facing strong opponents, and learning from failures, the characters in Haikyuu!! demonstrate the process of self-improvement and inspire viewers to strive for their own personal growth and development.