Reiji Arima is Soichiro's father. Reiji Arima, son of the Arima patriarch from an illegitimate relationship, was favored despite his status. His mother attempted to drown herself and take Reiji with her, but he saved himself by kicking her in the face—an event that haunted him throughout his life. Although gifted in music, Reiji led a troubled youth and was seduced by Ryoko, a beautiful woman seeking financial gain. She became pregnant, and Reiji named the child Sōichirō after his brother Shōji, though he had no further involvement in the child's life.
Years later, Reiji discovered that Ryoko had been abusing their son and had abandoned him. Unable to care for Soichiro himself, Reiji handed the child over to his brother Shouji before moving to New York City, where he eventually became a renowned jazz pianist. When Soichiro was in high school, Reiji returned to Japan and "kidnapped" his son to force him to spend ten days together. Later, he helped protect Soichiro from Ryoko, even threatening to kill her to prevent her from harming Soichiro again. Ultimately, he spared her life when Soichiro intervened, stopping him from shooting her. Reiji remains a very famous pianist living in America and only appears in the manga.
