Jack is Zack's brother, a mafia boss, Jack compared to Zack, he is a commander in the army. He is very well known and Zack is also well known. Jack and Zack are not blood brothers, Zack was adopted when he was 15 by Jack's family. Before being adopted, Zack had lived with Kaoru. Zack considered Kaoru his father, although there was a big difference in their ages.