Sensui was the former Spirit Detective before Yusuke Urameshi and was very good at his job. He is one of the main villains in Yu Yu Hakusho, and certainly the most crazy. He wants to open a tunnel between the Living World and Demon World so that demons can kill every human alive. Sensui doesn't even care if the world remains intact, he just wants humanity erased from the face of the earth. He even wants himself to be killed. He thinks everyone is diseased and that they all need to die. He thinks every human has the capability to be evil.

Sensui is one of Yusuke's most deadliest foes that Yusuke had to face during the whole series and was the closest villain to succeed in his original plan.