Yamaguchi's jump float serve becomes a weapon for Karasuno due to its unpredictability and ability to disrupt the opponents' reception. The serve is known for its unusual trajectory and speed variations, making it challenging for the receiving team to pass accurately. This puts pressure on the opponents, often leading to scoring opportunities for Karasuno. Additionally, Yamaguchi's jump float serve allows him to target specific players or areas on the court, further increasing its effectiveness as a strategic weapon.