"The ginzuishou... I want to see it, something that carries that much power. If I attack that planet, the queen will surely appear with it!" - Diamaund, Act 20
"but brother, you always do as you please..." - Safire to Diamaund, Act 16
Prince Diamaund is the leader of the Black Moon traitors from the future. His hair is white and straight, and he dresses in white with a white cape. He is arrogant, obsessive, and power-hungry.
As to his name: like his fellow Black Moon conspirators, his name refers to a jewel. He is like the diamond in more than name: he is cold, pale, and tough. The English spelling is all mine; the Japanese kana give him the name "De-ma-n-do," which is the closest possible approximation to the English "diamond." I should have called him "Diamond" or "Demando;" however, the form "Diamaund" pleases me. (It looks faintly regal and exotic.)
Diamaund is driven by two things: a twisted desire for power, and an intense longing for Neo-Queen Serenity. His quest for power brought him and his fellows to the planet Nemesis, where they cultivated the Evil Black Crystal. When they had become strong enough, they brought their forces to bear against Crystal Tokyo.
There, Diamaund saw a woman with beauty beyond his wildest dreams. Stunned, he admired the beautiful queen as he would a goddess... but her eyes defiantly rejected him; to her, he wasn't even human. Hurt, he struck out at her with his power; instead of being affected, she was suddenly encased in protective crystal, and taken away.
Diamaund couldn't forget her. He wanted to meet her again, to have her in his power, to make her kneel before him... in any form... he got a little hologram of her, which he'd stare at whenever he could... and he created a plan to capture the Sailormoon of the past. He brought her to Nemesis, where her powers were neutralized, and confessed his desire for her. He kissed her, but she shoved him away. Diamaund only laughed evilly. He could wait; Sailormoon wasn't going anywhere. And hadn't he waited for years until this point? She'd come around eventually.
This sort of attitude is indicative of Diamaund's attitude throughout the initial battles. He sees only what he thinks is there; he doesn't consider the fact that Usagi would never submit to him. Also, his brother Safire tends to be pessimistic and annoyed at Diamaund's tendency to rush into things; Diamaund sees this as a challenge to his power and therefore gives Safire's remarks little notice. Another case is his relationship with Wiseman; the Wiseman has but to tell him that he will gain power by doing a certain thing, and he will follow willingly. He does not see what Safire and Esmeraude suspected - that the Wiseman has a plan of his own.
It is Diamaund's one-sided vision that makes him so easy for Wiseman to control. However, he manages to break free of it. When Wiseman proposes to destroy the entire Earth, Diamaund comes to his senses. The deaths of Rubeus and Esmeraude suddenly hit home, and he realizes that the Wiseman has just been using them all along. He lashes out at the Wiseman and the Black Lady, and grabs the two ginzuishou of the past and the future. "I don't believe anyone any more!" he cries out. "I have the power..." He begins to touch them together, a fatal action.
Sailorpluto, at the expense of her own life, stops time. Usagi takes the crystals from Diamaund and transforms into Sailormoon. Then she and Tuxedo Kamen direct their power at Diamaund, and his body tears apart.
Diamaund and his fellow Black Moon conspirators had a pretty good plan to recreate history, and they almost succeeded. Unfortunately, they - especially Diamaund - were ignorant as to the true nature of the Wiseman, and they died for their blindness.
Credit goes to Ian Miller, who informs me that the term "demand" is archaic New High German for "diamond."