Ittetsu Hoshi, also known as Arthur Young, was a professional third baseman for the Yomiuri Giants from 1942 to 1948. His baseball career was interrupted by World War II military service, during which a shoulder injury permanently impaired his throwing. After returning, he developed the intimidating "Devil's Fastball," designed to appear as if targeting batters. Teammate Tetsuharu Kawakami condemned the pitch as dishonorable, leading to Ittetsu's retirement. Plunging into poverty in Doya-gai, he worked as a day laborer. The death of his wife Harue deepened his bitterness and alcoholism, and he projected his unfulfilled baseball ambitions onto his son Hyūma. He imposed extreme training regimens from Hyūma's childhood, including forcing him to use a heavy "Dai League Ball Training Cast" that stunted his physical development and dangerous drills such as hitting gasoline-soaked flaming baseballs at him. His coaching career included leading Seiun High School's baseball team, resigning just before the Tokyo tournament. Later, he rejected an offer from the Yomiuri Giants' second team and accepted a position as coach for the Chunichi Dragons, specifically to develop rivals capable of defeating Hyūma. He trained players like Ozuma and Chūta Ban using harsh methods, aiming to forge them into "assassins" against his son. His Dragons jersey number was 84, symbolizing that adding it to Hyūma's number 16 would achieve "perfection" through their conflict. Despite their adversarial relationship, he acknowledged Hyūma's sacrifices in their final showdown, and a moment of reconciliation occurred when he carried an injured Hyūma off the field. In later storylines, when Hyūma faced a career-threatening arm injury, Ittetsu shifted from antagonist to supporter, assisting his son's comeback while reflecting on his own past actions. His philosophy emphasized relentless perseverance, symbolized by references like the phoenix rising from ashes, and he declared that baseball extends beyond the stadium as a continuous twenty-four hour challenge.