As a child he was friends with Fuma Monou and his sister Kotori Monou. Kamui is the main character of X. He and his mother left Tokyo six year's ago after the death of Sayo Monou (Fuma and Kotori's mother). He has now returned to Tokyo only to discover that the fate of the world rests in his hands. Initially, Kamui is very cold, arrogant, and mistrustful, even to his childhood friends, Fuma and Kotori. However, Kamui is just trying to keep his distance to protect them from the chaos that surrounds him. When he lets his guard down, Kamui actually is a very caring and loyal person. More than anyone else, Kamui cares about and wishes to protect Fuma and Kotori. This desire to protect them and their future.