Sonic Onsoku, known as Speed-o'-Sound Sonic in the English adaptation, is a recurring character in the anime series One Punch Man. He is a highly skilled ninja and a self-proclaimed rival of Saitama, the series' protagonist. Despite his impressive speed and combat abilities, Sonic consistently finds himself outmatched by Saitama's overwhelming power. His character adds a humorous element to the series, as his serious and intense demeanor often leads to comical outcomes. Sonic's determination to defeat Saitama drives his continuous pursuit of strength and skill enhancement throughout the series.