|“||I always get everything I want. Everything.||„|
|~ Prince Diamond|
|“||Don't underestimate me!||„|
|~ Prince Demande while trying to finish off Wiseman|
Prince Diamond, also known as Prince Demand (プリンス・デマンド, Purinsu Demando, Prince Diamond in the English dub) and Prince Demande, is the leader of the Negamoon Family and the absolute ruler of the Negamoon. He was manipulated by Wiseman into attacking Crystal Tokyo and taking over the Earth. Finding Crystal Palace to be invincible, he sent one of his commanders, Rubeus, to the past to take over Tokyo by securing crystal points. However, Rubeus's plans were all foiled by Sailor Moon, and after his death, Diamond sent Emerald into the past to carry out her plan of taking over Tokyo by filling its vulnerable spots with dark energy. After several failed attempts, Diamond called her back.
Diamond is in love with Sailor Moon, and when she and the other Sailor Scouts went with Rini to the future, Diamond tried to hypnotize her into loving him, but Tuxedo Mask stopped him. After Emerald was destroyed, Diamond, Sapphire, Wiseman, and Wicked Lady (Rini brainwashed by Wiseman) traveled to the past and placed a dark crystal in the middle of Tokyo. Diamond's younger brother Sapphire discovered that Wiseman was conspiring against them, and tried to warn him, but was killed by Wiseman. Diamond was angry at Wiseman for this, but didn't believe Sapphire at first.
Sailor Moon came face to face with Diamond inside this crystal, where he unsuccessfully tried to hypnotize her. Soon, he realized that Sapphire was right about Wiseman, and fought him. Wiseman directed a dark spear attack at Sailor Moon, but Diamond jumped in front of her and took the hit. Though he managed to destroy Wiseman's arms (Wiseman came back together), he died from his injuries.
Diamond can shoot energy waves and energy balls (not unlike Dragonball Z style attacks), and hypnotize people with his third eye, which appears on his forehead whenever he uses it. Emerald is in love with Diamond, but he is in love with Sailor Moon.