Relationship

Sensui and Itsuki's relationship is very complex. When Sensui went on his many cases, Itsuki would watch him for hours. His obsession grew, and from the shadows Itsuki began killing apparitions that wanted Sensui dead. Eventually Sensui found out that Itsuki had been helping him and he wasn't grateful. To Sensui, Itsuki was just another demon. Sensui was about to kill Itsuki and asked if he had anything to say before he died. Itsuki had one final request. He wanted to live one more day. Sensui asked him why should he let him live and Itsuki said that tomorrow his favorite television show airs its final episode and that he wanted to see how it ends. Sensui laughed and told Itsuki he was the first demon to ever make him laugh. So he let Itsuki live.

From then on, Sensui and Itsuki were partners and went on many cases that Koenma assigned them. Their last mission however was the fateful mission that turned Sensui against humans. Itsuki didn't see the Feast of Human Vices. He walked into the room to find Sensui covered in blood. The only thing Sensui said was, "We're late, Itsuki. There weren't any humans when I came through the door; not a single soul."

Ten years later, Sensui gathered five psychics to help him open a tunnel between the Living World and Demon World. Itsuki is the main psychic opening the tunnel. Among anyone he's ever known, Itsuki has been the closest to Sensui. Itsuki loves Sensui, but Sensui has no loyalties and would be willing to sacrifice anything in order to meet his personal goals.