Rei is a man of few words who doesn't mind that Kazuki has already moved into his house. He is physically strong, and his fighting abilities and marksmanship are among the best in the industry. He has a clear separation between his professional and personal lives and spends most of his time at home playing video games. His family is a large underworld family, and his parents have been training him as a gifted assassin since he was a child. He has not been able to escape the family feud and has no comprehension of normal parent-child relationships.