Manabu Sakuma, known by the nickname Demon, is a high school student and a member of the Kaio Academy table tennis club. He is a childhood friend of Yutaka Hoshino, known as Peco, and their relationship is defined by both friendship and rivalry. Sakuma lacks natural talent for the sport but compensates through relentless hard work and dedication, often training with intense focus and discipline. His personality is marked by a combative streak and a fixation on defeating Peco, as he seeks to prove his worth and overcome his perceived limitations. Motivated by a desire to surpass his more naturally gifted friend, he joins Kaio because he believes it gives him the best chance to achieve that goal. In the story, Sakuma serves as a foil to characters like Peco and Smile, embodying the struggle between effort and innate ability. His development explores the emotional toll of chasing a dream through sheer perseverance, leading to moments of self-reflection when he confronts the gap between his ambitions and reality. On the table, Demon is known for a ferocious, aggressive playing style that reflects his inner drive. His key relationships extend beyond Peco to fellow Kaio teammates, though he initially appears isolated due to his single-minded focus. Through his arc, he learns about the value of camaraderie and the need to balance ambition with personal growth.