"[The ginzuishou] brings misfortune. All the power hidden in that stone... I will take that power. I won't be swayed by your words." - Wiseman to Sailormoon, Act 20
During the reign of Neo King Endymion and Neo Queen Serenity, a certain criminal came into power. All by himself, he almost brought Crystal Tokyo to ruin. Crime ran rampant in the streets; people were fighting and dying. It was a horrible time.
The criminal's name was Death Phantom. He had the special abilities of "death hands" and "evil vision." His "death hands," cloudy arms, could reach any distance and kill with a touch. His "evil vision" could also bring death wherever he chose to look; he could also control other people's minds. Death Phantom was human, but with his special powers, the queen and her senshi were unable to kill him.
However, they were able to defeat him. When they had him subdued and under control, Neo Queen Serenity banished him to the farthest reaches of the Solar System. The cursed tenth planet, Nemesis, was dark and distant; it was unlikely (without the help of technology) that Death Phantom would be able to escape there. From that point on, Nemesis was a restricted planet. Nobody was allowed to go there anymore, for fear that Death Phantom would be able to control their minds or hurt their bodies.
Faced with this situation, Death Phantom searched for a way to retaliate against Crystal Tokyo and gain the ginzuishou of power. Somehow, he was able to infuse his consciousness into the very planet. Slowly, Nemesis and Death Phantom became one and the same spirit.
Death Phantom / Nemesis then reached out with his mind to Earth, and looked for discontent. He found it; four young people were staring resentfully at the beautiful palace in Crystal Tokyo. "Why should they have all the power?" they complained. "It's blasphemous for mere humans to live so long."
Death Phantom cloaked his decaying body, and sent his image to them. He spoke into their minds. "Young traitors," he whispered. "If you want power, go to the tenth planet, Nemesis. If you want to have everything... get the Evil Black Crystal."
Those young people happened to be Diamaund, Safire, Rubeus, and Esmeraude. Calling himself "Wiseman," Death Phantom was able to manipulate the four young people - especially Diamaund - into carrying out his plans. They charged up the Evil Black Crystal, infusing Nemesis with its dark energy. The forces of the Black Moon also weakened the senshi, reducing their numbers and constantly attacking them. Finally, Death Phantom got an unexpected stroke of luck - he ran into Chibiusa. She was wandering around, lost in the warp of space-time, alone and afraid.
He spoke to her comfortingly, coaxingly. "You can't come any farther without saying farewell to your world," he told her gently. He held out a cloudy hand. "Take my hand. Come with me." Hesitantly, Chibiusa put her small hand in his.
He made her into the Black Lady.
The Black Lady had enormous power, and her goals complemented Death Phantom's. Diamaund came to his senses and blasted Wiseman's cloaked form, but there was only a skeleton inside. The Black Lady only laughed and revealed that Wiseman had not really been human; that, indeed, Wiseman was the planet Nemesis. The Black Lady's powers, enhanced by Wiseman's, were nearly unstoppable. Soon, they had both the past and future ginzuishou in their hands...
...at which point Diamaund grabbed the two crystals, and made as if to touch them together. Sailorpluto stopped time and died because of it; her death shocked Chibiusa back to her original form, and gained time for Usagi and Mamoru to recover.
Nemesis was not about to let them go. He created a massive energy swirl, sucking them in. But Sailormoon, Tuxedo Kamen, and the newly-awakened Sailorchibimoon combined their strengths, calling on all the power of the past and future ginzuishou. "Moon Princess Halation!" the two girls cried, attacking with everything that they had.
The dark planet shattered into nothingness.