Kagemitsu is a intelligent and dedicated person, just like his son, Black Jack is. He cares for his family so much he was forced to flee to Macau, China with his new wife, fearing that the Noir Project organization will come after them.
Kagemitsu works as a hospital staff at a hospital in New York. There, he met Mio who also works at the same hospital as a nurse. He left his job and decided to join the Nior Project, a secret project which famous world doctors are also involved. One day, he reunited with Mio once again after returning to save his friend's wife by giving a mechanical heart he created in the project. At Central Park, he confesses his love to Mio and went to Japan to get married. There, Black Jack was born. After refusing to resume the Noir Project, the organization threatens him by placing a bomb at the beach where Black Jack and Mio were. The bomb blew up, nearly killing them and Kagemitsu was forced to run away to Macau, China with his new wife, fearing for his family's safety.
In China, Kagemitsu started a new family with his new wife. He was reunited once again with his son, Black Jack and asked him to operate on his wife's face. During a father and son conversation, he lied by saying that he doesn't love Mio for the sake of protecting his family for 21 years. Later, he fell into a coma for a few days and passed away soon after.