Prince Demand (プリンス・デマンド, Purinsu Demando?, Prince Diamond in the English dub) is the leader of all of Planet Nemesis in the 30th century.
Born on a prisoners' planet, Demand originally intended to reason with Neo-Queen Serenity, explaining that he and his people are descendants of criminals, not criminals themselves. Wiseman manipulates the young prince to be unforgiving to the people of Earth. During an attack on Crystal Tokyo, Prince Demand sees Neo-Queen Serenity and falls in love with her. He is fascinated with her eyes, and the anger they bore toward him during the glimpse they caught of each other.
In the anime, the people of the Black Moon Clan refused the purification offered by Neo-Queen Serenity at the formation of Crystal Tokyo, and were subsequently banished to the planet Nemesis. Prince Demand led his people as they sought revenge on the people responsible for their banishment, despite the fact that he was infatuated with the Queen.
When Demand went to the past and encountered Sailor Moon, he recognized her as the past form of the future queen, kidnapped her, and dressed her up to suit him, but she was saved by Tuxedo Mask. When she and the other Sailor Senshi made a frontal assault on the forces of the Black Moon he found her again and tried to use his powers to force her to love him, but his efforts failed.
Between what Sailor Moon said and what he remembered Saphir trying to tell him, Demand came to realize that Wiseman was using him. When Wiseman tried to kill Sailor Moon, Demand saved her at the cost of his own life.