Prince Demande is the yandre to Usagi/Sailor Moon in the Black Moon Arc/ Sailor Moon R.
Black Moon Arc
Prince Demande resented Crystal Tokyo, believing them to be corrupt and that their lifespans were profane. Wiseman approached him and convinced him to use the power of theEvil Black Crystal, Demande planned to use the power of the crystal to time travel and create a new history before the reign of the Moon Kingdom. When the Black Moon Clan attacked Crystal Tokyo the first time Neo-Queen Serenity went to find her daughter, Chibiusa. Prince Demande then became obsessed with the Queen and kidnapped Sailor Moon, whom he realized was the same person. After waking up in Nemesisshe tried to transform but came to realize the dark energy of the planet had absorbed her powers. However she managed to escape with her friends and caused the palace to collapse. After losing Sailor Moon, Prince Demande realizes he was simply being used by Wiseman and revolted against him. In the process Demande was forced to kill his brother and used the Silver Crystal he got from Sailor Moon and another from from the future Black Lady to destroy the space-time continuum. His plan was stopped by Sailor Pluto. After this he attempted to kill Sailor Moon, but was killed instead by Sailor Moon and Tuxedo Mask.
Sailor Moon R
Demande first sent Rubeus into the past, but Rubeus was defeated by the Sailor Senshi, and destroyed along with his ship. Esmeraude was then sent into the past, but the Sailor Senshi kept foiling her plans. Esmeraude was in love with Prince Demande. After her death, Demande's younger brother Saphir found out that Wiseman was only using them for his own twisted goals, and attempted to warn him, but was killed by Wiseman.
Shortly after, Demande attempted to hypnotize Sailor Moon so he could rule the universe with her by his side as his queen, and was about to kiss her, but Tuxedo Mask comes and rescues her.
Later he hypnotizes Sailor Moon again and nearly succeeds in winning her, but then she remembers her friends, Mamoru and escapes Demande's hypnotic powers. She was able to warn him about Wiseman's deception. Enraged, he turns on him up learning that he had killed Saphir in trying to warn him about the treachery. When Wiseman directed two dark energy blades at Sailor Moon, Demande jumped in front of her and took the hit, and died as a result of this injury. However, he was able to damage Wiseman, shattering his arms, but Wiseman came back together. Before his death Demande was able to tell Sailor Moon his true feelings for her - he did love her as a person.
- The spelling of his name is inconsistent. It is sometimes spelled as "Prince Diamond", "Prince Demand", "Prince Demond", "Prince Diamand", "Prince Demando", "Prince Diamonde" and "Prince Daimande". The English rerelease manga spells his name as "Prince Demande".
- He is showed to be obsessed with Neo-Queen Serenity and even kissing Usagi on the lips, implying that he is in love with her.